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\medskip
\centerline {\Large \bf Development of a Superconducting Heterodyne Camera} 
\centerline {\Large \bf for Submillimeter-wave Astronomy} 
  
\section{Introduction}
           
The advent of large format ($\sim$100 pixel) spectroscopic imaging cameras at
submillimeter wavelengths will fundamentally change the way 
astronomy is performed in this important wavelength regime. While the 
possibility of such instruments has been discussed for more than two decades
[1], 
only recently have advances in mixer technology, device fabrication, 
micromachining, digital signal processing, and telescope design made the 
construction of such an instrument possible and economical. Here we propose
to implement these technologies to develop the first integrated submillimeter
heterodyne arrays. The arrays will utilize the latest Nb and Nb-Au
diffusion cooled 
Hot Electron Bolometers (HEB) in an efficient, micromachined, waveguide
mount. HEBs are inherently broadband, require very little local 
oscillator (LO) power (diffusion cooled HEBs require $\sim$30 times less 
LO power than SIS tunnel junctions), and no required magnetic field. 
They are
also relatively simple structures, making fabrication easier than SIS
and device-to-device performance more uniform. These properties make
HEBs ideal for array applications. The noise performance of HEBs starts
to become competitive with SIS mixing devices at $\sim 1$~THz and HEBs are
the most sensitive mixer technology above 1.4~THz. It is in this
frequency range where laser micromachining can be used to fabricate
efficient, compact arrays of feedhorns and waveguide structures
[2]. These facts, combined with the availability of local
oscillators, telescopes, and the ability to intercompare mixer
performance with existing SIS receivers, prompts us to build the first
prototype arrays for operation in the astrophysically important
350~$\mu$m (850~GHz) atmospheric window. The goal of the proposed effort is to
demonstrate the viability of large format arrays by constructing a
prototype 4x4 array, conducting extensive laboratory testing, and then
using it for astronomical observations. The system design is one that
can be scaled up to much larger size (10x10 or larger should
be feasible) and higher frequencies (to at least 3 THz).

Arrays only reach their true potential if the performance of each
pixel approaches that of an optimized individual detector. We will
therefore begin by constructing prototype single channel versions
of the array pixels. Once these are optimized, we will construct
1-D arrays ($1\times 4$) and ultimately stack them to make 2-D arrays
($4\times4$).  We will initially use the best Nb HEBs available and
then upgrade to Nb-Au HEBs, both provided by the Yale group. 
The micromachined waveguide mounts, IF/bias electronics, cryogenics, 
optics, and spectrometers will be provided by the Arizona group.
Both groups will work together on instrument characterization 
and astrophysical observations. 

The prototype arrays will be initially used on the 10~m Heinrich Hertz 
Telescope (HHT) operated by the University of Arizona on Mt. Graham, AZ. 
Once the arrays have been fully characterized, they, or
a copy of them, could also be deployed on the 1.7~m AST/RO telescope at
the South Pole. The deployment would occur after the proposed work. 
The PI and his collaborators already have a 4-channel,
810~GHz SIS array (PoleSTAR) in operation on AST/RO [3]. The
experience gained in building PoleSTAR will be fully utilized in
the development of the proposed integrated array.
Here we request funding only for the development of the HEB arrays 
and testing on the HHT. 

Our hope is that this work will lead to the availability of relatively
low-cost, sensitive arrays that could revolutionize submillimeter
astronomy as arrays have already done in the infrared over the 
past two decades. 

\section {Scientific Motivation}

We propose to construct an integrated, low-noise, $4\times 4$,
superconducting heterodyne camera (SuperCam) for the 350~$\mu$m atmospheric 
window. Through this effort, we will further the development of key
technologies required to build large format arrays in the submillimeter 
and THz regimes. While its principle purpose is to serve as a technology 
testbed, the proposed 16-channel 810~GHz array will be a unique, 
powerful instrument in its own right. 

\begin{figure}[!hbt]
\centering
\begin{minipage}{7in}
\parbox{4.25in}{\includegraphics[scale=0.45,angle=0]{transplot.eps}}
\parbox{2.25in}{\caption{\label{trans} {\small Submillimeter atmospheric
transparency for the HHT on Mt. Graham and AST/RO, SPT at the
South Pole. Precipitable water vapor is 1~mm at Mt. Graham, and
0.25~mm at the Pole.}}}
\end{minipage}
\end{figure}

The atomic and molecular transitions accessible in this spectral range
are important diagnostics of a variety of astronomical phenomena
including planetary atmospheres, molecular clouds, star-forming
regions, young stellar objects, circumstellar envelopes, and planetary
nebulae.  Yet, the 850 GHz atmospheric window remains relatively
unexplored, due to poor atmospheric transmission and the relative
difficulty of constructing sensitive receivers at high frequencies.  
Figure 1 depicts the atmospheric transmission curves for Mt. Graham
(lower) and the South Pole (upper), possible 10-20\% and 50\% of the
time during the winter at each site, respectively [4]. 
Labels mark spectral lines of highest importance, and their
frequencies and diagnostic capability are tabulated in
Table~\ref{tablelines}.  Heterodyne receiver arrays will maximize the
scientific return from transient periods of superb submillimeter
weather conditions, and will revolutionize the spectral line mapping
of interstellar clouds.  For illustration, Figure 2 (left)
portrays the footprint of the 16-element array on the sky, and the portion
of the Eagle Nebula (M16) molecular cloud that can be mapped in one 
6-hour shift at the HHT with 1, 4, and 16 pixels.
Figure~\ref{mappingspeed}(right) 
illustrates the footprint of a possible future 91-pixel array on AST/RO at
the South Pole. This array would be a straightforward extension of the
technology that will be implemented in the proposed 16-pixel system.
With such an instrument, 1000 square arcminutes can be fully sampled
with a $\sim 50''$ beam in only 4 hours to $T_{RMS} = 0.5$~K during
median winter observing conditions at the Pole.


\begin{table}[!hbt]
\centering
\begin{tabular}{|lccl|}
\hline
{\bf Species} & {\bf Transition} & {\bf Frequency (GHz)} & {\bf
Importance} \\
\hline \hline
$^{12}$CO & J=$7 \rightarrow 6$ & 806.652 &  - Excitation and structure \\
$^{13}$CO & J=$8 \rightarrow 7$ & 881.273 &  \ of molecular clouds; PDR's,\\
C$^{18}$O & J=$8 \rightarrow 7$ & 877.922 &  \ shocks, protostellar
outflows, \\
$^{12}$C atom & $^3P_2 - ^3P_1$ & 809.343 &  \ \& star-forming regions \\
\hline
CO$^+$ & J=$7 \rightarrow 6$ &  825.639 &  - Molecules in hostile
environments,\\
 & & & UV and X-ray dominated regions \\
\hline
$^{13}$C atom & $^3P_2 - ^3P_1$ & 809.124 &  - Abundance of $^{13}$C and
$^{12}$C, \\
 & & & \& \ Galactic chemical evolution \\
\hline
HCN &  J=$10 \rightarrow 9$ & 885.971 &  - Dense gas in molecular cloud cores \\
\hline
HCO$^+$ & J=$9 \rightarrow 8$ & 802.458 & - Excitation and kinematics of\\
HCO$^+$ & J=$10 \rightarrow 9$ & 891.558 &  \ YSO envelopes, protostellar collapse \\
\hline
HCN & $\nu=1_c$, J=$10 \rightarrow 9$ & 885.855 & - Dense/IR-pumped gas\\
HCN & $\nu=1_d$, J=$10 \rightarrow 9$ & 890.334 & \ in YSO circumstellar disks\\
\hline
SiO &  J=$20 \rightarrow 19$ &  867.457 &  \ - Stellar ejecta; molecular shocks \\

\hline

\end{tabular}
\caption{\label{tablelines} {\small Selected spectral line diagnostics in the
850 GHz atmospheric window}}
\end{table}


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.45,angle=0]{810-smt-3bw.eps}
\includegraphics[scale=0.30,angle=0]{supercam-astro-bw.eps}
\begin{minipage}{6.5in}
{\parbox{3.5in}{a)}}
{\parbox{3.5in}{b)}}
\end{minipage}
\caption{\label{mappingspeed} {\small Heterodyne receiver arrays will
revolutionize the mapping of molecular clouds and star forming
regions.  a) The prototype 16-pixel 810 GHz array can fully sample the M16
molecular cloud at 9'' resolution in CO~J~=~$J=7 \rightarrow 6$ to 0.5~K~RMS in one 6-hour shift, with a very conservative T$_{sys}$ of
20,000K.  b) Based on the technology developed for the proposed array
a large format, 91-pixel, array could be constructed for AST/RO. With
the array, 1000 arcmin$^2$ could be mapped in $\leq$4 hours
($T_{sys}=10,000$, 0.5~K~RMS). }}
\end{figure}

Lines in the 850~GHz atmospheric window share a number of common traits; all
probe warmer, denser environments ($T \sim 100$ K, $n \sim 10^{5-9}\ {\rm
cm}^{-3}$) than typically observed at millimeter wavelengths.  These properties
make them unique and powerful probes of energetic molecular gas
which provides the crucial link between luminous stars, their remnant
descendants, and the cold molecular clouds that form them and are
subsequently destroyed by them. 
The following sections describe several science objectives
for large-format submillimeter arrays on ground-based
submillimeter telescopes, initiated by the 16-pixel array at the HHT
and extended in future $\sim 10 \times 10$ pixel second-generation
instruments for AST/RO and, ultimately, the 8-meter South Pole Telescope
(SPT). 

\subsection{Science with a 16-pixel Array at the HHT}

A number of pivotal science objectives are ideally suited to the 9''
beam size and $\sim 0.1$~km~s$^{-1}$ spectral resolution afforded by the
proposed instrument on the HHT.  Among these are studies of molecular 
cloud physics/chemistry, evolved stars, and protostellar 
evolution. Once the instrument is comissioned on the HHT, it will be 
available for use by the national and international community. Here we 
will limit our discussion to a few possible reseach topics.

\begin{figure}[!hbt]
\centering
\begin{minipage}{6.5in}
\parbox{4.3in}{\includegraphics[scale=0.65,angle=0]{orion-bw.eps}}
\parbox{2.0in}{\caption{\label{orion} {\small Integrated intensity of the 
J~=~$7 \rightarrow 6$ line of CO from the Orion molecular cloud,
observed at the HHT (Wilson et al. 2001).  The intensity scale is
shown as a bar on the 
right side of the map. Selected positions of the map have been
measured in the 1.037 THz line of CO~J~=~$9 \rightarrow 8$ from the
HHT (Kawamura et al. 2001), displayed on the far right.  This
demonstrates the feasibility of near-THz submillimeter astronomy from
ground-based observatories. }}}
\end{minipage}
\end{figure}

\subsubsection{Mapping of Star Forming Cloud Cores}

One of the major goals of ground, airborne, and space-based
observational astronomy is the identification and study of
protostellar objects.  A study of protostars provides insight into
the initial conditions required for star formation, protostellar
evolution, and the formation of solar systems like our own. 
Accessibility of high-J CO, HCO$^+$ and HCN lines will probe
the physical conditions of the dense, hot envelope gas located much closer 
to the protostar than is currently accessible at lower frequencies
[e.g. 5,6 and references therein].
The study of the excitation and structure of star-forming cores versus
starless cores is an exciting prospect.  Figure 3
demonstrates the feasibility of doing such science at the HHT, with CO
J~=~$7 \rightarrow 6$ and 1.037 THz CO J~=~$9 \rightarrow 8$ mapping
of the Orion cloud core [7,8]. 
Furthermore, the excitation and abundance of HCO$^+$~J=$9\rightarrow
8$ and J=$10\rightarrow 9$, with $n_{crit} \sim 10^{8-9}\ {\rm
cm}^{-3}$ directly reflects the ambient radiation field, provides an
estimate of ionization fraction, and kinematics of protostellar
envelopes.  Indeed, direct detection of infall is 
tractable through these transitions, as the inner envelope is expected
to collapse faster than the colder outer envelope traditionally probed
at lower frequencies.  Linewidth correlations of CO and HCO$^+$
at low- and high-J would then be expected.  The high angular coverage
and resolution provided by the proposed array is critical for
disentangling the complicated kinematics of star-forming environments.  

\subsubsection{Circumstellar Disks}

Detection of circumstellar material around young stellar objects
remains a difficult, but crucial challenge to a complete understanding
of star formation.  Debris disks have been observed in the infrared,
yet the gaseous content of circumstellar disks remains uncertain.
Only two systems were detected in rotational H$_2$ emission by ISO,
and only a handful of CO disks have been studied by mm-wave
interferometers.  A comprehensive understanding of the properties of
circumstellar disks is a prerequisite to a meaningful theory of planet
formation and its unambiguous detection.  Vibrationally-excited
emission of HCN, located adjacent to the pure rotational lines
provides a means of exploring
the gaseous environments in circumstellar disks [9, references therein].  
If vibrational transitions are collisionally excited, the gas density and
temperature must be of order 10$^{11}$ cm$^{-3}$ and T$\sim 1000$K,
probing energetic gas in circumstellar environments, and easily
compared to the less-energetic requirements of the pure rotational lines.
Alternatively, the excitation of the $v_2$ mode may be due
to the radiative pumping of infrared light in the disk or inner
envelope, and if this is the case, the mean radiation field and kinematics
can be assessed.  A measurement of the intensity ratio of the 885 and 
890~GHz lines of the $v_2$ bending mode of HCN will allow determination 
of the mechanism, as the radiative cascade to the ground state has a 
detectable non-LTE signature.  With its unique angular coverage, the proposed 
16-pixel array will probe both circumstellar disks and the complex interaction
of circumstellar material with the molecular envelope and cloud core
in which it is embedded.  This alone represents a significant test of
theoretical models.


\subsubsection{The Large Scale Structure of Molecular Clouds}

It is widely accepted that the evolution of molecular clouds plays a
pivotal role in the initial stages of star formation.  
With the recent advent of sensitive submillimeter heterodyne receivers
and telescopes, it is generally recognized that molecular clouds can often
harbor copious volumes of warm dense gas that has a different spatial
distribution than large-scale CO J=1-0 emission [e.g. 10]. 
This serves as the observational basis for theories of the structure and
excitation of molecular clouds.  The excitation of warm gas can be
radiative or collisional, and each excitation type probes different 
astrophysical phenomena pivotal to the evolution of the cloud.  

{\it Collisional excitation} of warm gas in these regions often stems
from shocks, principal sources including interstellar turbulence,
collisions between kinematically-distinct cloud components, and
powerful outflows from protostars.  The chemistry and
dynamics of molecular outflows, in particular, is a topic of
timely study with fundamental unanswered questions.  
For example, CO J=1-0 and 2-1
outflow studies are likely missing a substantial fraction of the CO
mass participating in some outflows, leading to an 
underestimate of their raw mechanical power. 
In contrast, {\it radiative excitation} often stems from the warm
photodissociation (PDR) fronts at the illuminated surfaces of molecular
clouds.  Optically thick CO J=7-6 emission (806 GHz) probes the density and
temperature structure of molecular gas at the CO ``photosphere'', and
optically thin emission from the fine structure lines of atomic carbon
(809 GHz) probes the dissociation of CO and the recombination of C$^+$
at these ionic-atomic-molecular interfaces [11].  The structure and physics
of PDRs relate directly to the ability of a molecular cloud to shield
itself from the interstellar radiation field, and hence its lifetime.

The high resolution provided by the proposed array at the HHT is
optimized for large scale ($\sim1^o$) 1-dimensional mapping
(i.e. RA+DEC ``slices'') of important molecular clouds and cloud
cores.  Fully sampled 2-dimensional maps would be ideally suited to
the excellent submillimeter observing conditions and larger beam size
at AST/RO. 

\subsubsection{Stellar Ejecta}

Mass loss from cool evolved stars is a major source of both dust and
gas in the ISM.  The ejected matter is usually molecular and can have a
wide range of excitation.  Recent studies of the molecular component of
the old planetary nebula NGC 7293 (``The Helix'') [12]
show that such ejected molecular gas survives in a highly clumped,
complex structure of large extent (1000$^{\prime\prime}$ x 800$^{\prime\prime}$).  
Other much younger
planetaries like NGC 7027 have molecular envelopes surrounding the
ionized zone with extents of 1$^\prime$ or more [13],
containing a PDR at the interface [14].  Tracing the
structure of such molecular gas in the high-excitation lines accessible
to the proposed array will be a key to understanding the mass loss
process from evolved stars and subsequent dispersal in the ISM.
Besides the CO $J=7\rightarrow 6$ line, several other molecular tracers will be
useful for mapping, including the HCN $J=10\rightarrow 9$ line, which should be
prominent in carbon-rich stars (like NGC 7027) and SiO $J=20\rightarrow 19$, an
important component of the envelopes of oxygen-rich ejecta.  The rapid,
sensitive mapping capability of the array will allow us to determine
the distribution and kinematics even of structures as large the Helix
Nebula.


\section {Technical Description}

In the past the fabrication of integrated arrays of heterodyne mixers
at submillimeter wavelength was prohibited by several factors:
\begin{itemize}
\setlength{\topsep}{-1ex}
\setlength{\partopsep}{-1ex}
\setlength{\itemsep}{-0.4ex}
\setlength{\parsep}{-0.4ex}

\item Sensitive mixing devices either did not exist or were difficult to
   fabricate.

\item When mixers were available, their performance would often vary
   significantly from device to device.

\item There was insufficient LO power to efficiently pump more than
   one or two detectors at any given time.

\item Stacking more than a few mixer blocks together in the focal plane
   with their associated backshorts (if necessary), IF amps, magnets,
   bias lines, etc. was mechanically complex and could overload the
   cryogenic system.

\item The cost of the frontend components and the required backend
   spectrometer were prohibitive.

\end{itemize}

However, through the arduous efforts of many researchers in the
field, most of these hurdles have now been overcome. In the following
sections, we will describe plans for an instrument that combines a number 
of leading edge technologies to make a compact, sensitive 
submillimeter heterodyne array.      

\subsection {HEBs for Array Applications}

	Submillimeter heterodyne receivers have advanced dramatically in
the past decade, and these advances will be incorporated, and further
developed, in new missions such as SOFIA and Herschel/FIRST.  Up to 1~THz,
almost all (cryogenic) receivers use niobium (Nb) based SIS mixers.  SIS mixers
will likely be used to 1.2~THz in the future, with a likely upper limit of
about 1.4~THz due to film losses and junction gap frequency for known film
materials and devices [15]. The LO power is of order 1~$\mu$ W.  Below 
0.7~THz, the receiver noise (DSB) is approximately (2 to 4) $\times T_Q$ with 
$T_Q =hf/k_B = 48~K \times f(THz) (e.g. T_Q = 40~K$ at 0.8~THz). Above 0.8 THz, 
the noise rises to a larger value than this formula, due to losses in the film
circuit used to resonate out the SIS junction capacitance.  Schottky
mixers are presently employed at frequencies above 1~THz [e.g. 16]. 
Hot Electron Bolometer (HEB) mixers with much lower noise and $P_{LO}$ are now
ready for use in this higher frequency range [17]. 

       The HEB mixer consists of a narrow, thin superconducting 
microbridge contacted with thick normal-metal films (see Figure 4a and 4b).
The simplicity of their construction does in fact minimize the device-to-device
variation in performance often observed in more complicated structures such
as SIS junctions. HEB mixers use the heating of electrons at the superconducting
transition temperature, $T_c$ to accomplish the mixing.  The resistance oscillates 
at the IF due the combined LO and signal power [18].  The conversion efficiency is 
typically good (-8 to -10~dB), and there is no capacitance (as there is for SIS) 
and no gap frequency limit.  Thus, coupling to broadband planar antennas or 
waveguide structures is
feasible to 10~THz or higher.  Two mechanisms of electron cooling are
used:  hot-electron outdiffusion (first proposed and studied by the
co-PI) [19] and phonon cooling [20]. Both diffusion cooled Nb HEBs and 
phonon cooled NbN HEBs have achieved comparable low receiver noise 
temperatures ($T_R$) above 2~THz with large IF bandwidth, 9~GHz.
The limit on $T_R$ appears to be set by thermal fluctuations [21, 22] 
and this argues that devices which operate at a lower temperature -
with lower $T_c$ should have improved performance. We find this to be
the case for diffusion cooled devices. For phonon-cooled devices there are, at
present, no materials which would allow this $T_c$ reduction, given the required 
IF bandwidth of 1-2~GHz.

\begin{figure}[!htb]
\centering
\begin{minipage}{7in}
\parbox{4.5in}{\includegraphics[scale=0.35,angle=0]{heb3.ps}
\includegraphics[scale=0.3,angle=0]{heb2.ps}}
\parbox{2.0in}{\caption{\small Morphology of an HEB. {\bf (a)}
Schematic of an HEB. {\bf (b)} Scanning Electron Micrograph (SEM) of a
Nb-Au HEB produced at Yale.}}
\end{minipage}
\end{figure}

HEB mixers promise to achieve noise of a few times $T_Q$.
At 2.5~THz, $T_R$ = 1800~K (DSB)
measured with a large IF bandwidth, 9~GHz, and mixer noise was $T_M$ = 350~K.
An 810~GHz, phonon-cooled HEB receiver built by the Center for Astrophysics 
has been in operation on the Arizona/MPIfR 10m Heinrich Hertz Telescope
(HHT) for several years [8]. The double sideband noise temperature 
of the receiver is ~800~K. With Nb-Au diffusion cooled HEB, the receiver 
noise temperature is expected to be less than $\sim$1/3 this value, comparable to 
what can be achieved with Nb SIS devices. However, an HEB utilizes 10-100 
times less LO power, requires no magnetic field, and has a much broader 
bandwidth. These characteristics make HEBs a better choice for focal
plane arrays, even though SIS devices of similar sensitivity are available. 
For example, with SIS devices, variations of junction area (and therefore
capacitance) lead to variation of resonant frequency from device to device,
making uniform THz arrays extremely difficult to realize.

	The Yale group has studied (with JPL) diffusion cooled Nb HEBs [23].
Devices were produced at JPL.  $T_c$ was 5 to 6~K.  Microwave mixing at 20-40
GHz was studied at Yale, and mixing at 0.6, 1.2 and 2.5~THz was studied at
JPL.  The microwave studies can be done quickly, with no background noise,
and with known coupling.  The Yale findings correspond reasonably well
with those at JPL, once the THz losses are accounted for. These
Yale-JPL studies confirm most of the basic predictions for diffusion
cooled HEBs: IF bandwidth is determined by the out-diffusion time and thus
controlled by the length; the noise is dominated by thermal fluctuations.  The
noise is thus expected to scale with $T_c$.  Thus, studies at Yale and JPL
first tested aluminum HEBs, with $T_c = 1$ to 2~K.  These indeed have the low
noise predicted, but the dynamic range is quite limited, due to output
saturation.  This is partly due to the lower $T_c$ (1~K for the Yale
devices), but also due to the long coherence length of Al.

In the past year the Yale group has developed a lower-$T_c$ Nb HEB,
using a superconducting Nb-Au bilayer [24]. The 10-nm Au thickness reduces $T_c$
to 1.6~K. {\it Fabrication was done at Yale}.  The IF bandwidth is 1.3~GHz, and
can be much larger with a shorter device.  Device properties are
summarized in Table 2. The Nb-Au HEB mixers display very low $T_M$ and for
these, the quantum noise, $T_Q$, will contribute at THz frequencies.  Of
course, that is the ideal limiting situation.  Because of the short
coherence length in Nb-Au, the dynamic range is much larger than for the
Al HEBs [25]. The required LO power ($P_{LO} = 2$~nW) is also larger than 
for Al, which reduces or eliminates problems with saturation.
For the device studied, with $T_c$ = 1.6~K, no output
saturation is expected, and input (rf) saturation is also not expected
with moderate rf bandwidth, 200~GHz, since the rf background is 
$<<P_{LO}$.  For larger rf bandwidths ($> 0.5$~THz), an increased $T_c$ would 
be used, with thinner Au, to obtain larger $P_{LO}$, which scales [26] 
as $T_c^2$ for a given material. Nb-Au has larger $P_{LO}$ for the same 
$T_c$, compared to Nb, but still low noise. Thus, the Nb-Au system is 
appropriate for a large range of future THz applications. The low required 
$P_{LO}$ and low noise make these Nb-Au HEBs ideal for sensitive array 
applications, into the few THz range at least [27].

\begin{table}[!hbt]
\centering
\begin{tabular}{|ccccc|}
\hline
 & $T_c$ & $T_M$ & $T_R$ & $P_{LO}$ \\
\hline \hline
Nb  ( 2.5 THz)  & 5-6 K  &  350 K  &   1800 K & 20-40 nW \\
Nb  (30 GHz)    &  5 K   &  200 K  &   \dots & 6 nW \\
Nb-Au (30 GHz)  & 1.6 K   & 50 K    &   \dots &   2 nW \\
\hline
\end{tabular}
\caption{\label{put-label-here} {\small Summary of HEB properties}}
\end{table}

%(In REFs =Superconducting bilayers with much lower Tc are used for
%single-photon and direct detection; for that application diffusion cooling
%is minimized; these are known as TESs.)
%Ta HEBs with $T_c = 2$~K may also function well in low noise
%applications (Ref - boris article).


\subsection {Micromachined Waveguide Mounts}

HEBs have been successfully used in both quasi-optical and waveguide
mixer mounts [22,8]. When waveguide and quasi-
optical mixers are made at the same frequency with comparable mixing devices, 
laboratory measurements show waveguide mixers outperform quasi-optical 
mixers both electrically and optically [28,29,30]. This occurs because waveguide 
has an intrinsically lower loss than the microstrip structures used in
planar designs and waveguide feedhorns can couple
to the fundamental Gaussian mode with a ~98\% efficiency, compared
to the $\leq$ 89\% efficiency of dielectric lens-planar antennas [31]. 
 
At wavelengths shorter than 400~$\mu$m (800~GHz), rectangular waveguide
structures, feedhorns, and backshorts become extremely difficult to
fabricate using standard machining techniques. We have used a new laser
milling technique to fabricate high quality, THz waveguide components and
feedhorns. Once metallized, the structures have the properties of standard
waveguide components [2]. With this process, waveguide
components of varying height and width can be machined quickly
and at low cost to an accuracy of $\sim 1$~$\mu$m.  
By combining this new laser micromachining process with HEBs, 
the construction of high performance, large format, waveguide 
imaging arrays at THz frequencies becomes possible.

As an example of a laser micromachined part, proof-of-concept
810~GHz and 2~THz corrugated feedhorns were fabricated. The 810~GHz
feedhorn includes a circular to rectangular waveguide transition
with $\lambda/4$ steps to quarter height guide. Figure 5 shows a portion 
of the waveguide structure etched in 1 hour (a duplicate mating piece was 
also fabricated). A $1\times 4$ array of corrugated feedhorns 
(see Section 3.3) could be made in $\sim$1 day.   
 
\begin{figure}[!htb]
\centering
\includegraphics[scale=0.30,angle=0]{fig3a_m.ps}
\includegraphics[scale=0.30,angle=0]{fig3b_m.ps}
\caption{\small SEM of portion of
an 810~GHz feedhorn structure. The structure was etched using 4.3
Watts of laser power focused into a 6 $\mu$m spot in 200 Torr of
chlorine gas.  The laser beam was scanned at 5~cm/s and incrementally
moved 2~$\mu$m  between line scans.  Under these conditions,
nominally 1~$\mu$m shavings are removed per pass of the laser over the
surface.  The total etch time is one hour, not including the overhead
time for pattern generation and stage motion.  {\bf (b)} SEM close-up
of ridges.}
\end{figure}

As a test of our fabrication and assembly process, we performed beam
pattern measurements on a laser micromachined 2~THz corrugated
feedhorn [2]. The differences between the theoretical and measured beam
profiles were within the resolution limit and amplitude sensitivity of
the test set-up.

Waveguide surface roughness values measured with atomic force
microscopy are typically on the order of 200 nm RMS. This surface
quality is already sufficient to provide low-loss waveguide
performance to $\ge 10$~THz.  The RMS surface roughness can be reduced
even further, to under 25~nm, using standard polishing etches based on
HF-HNO$_3$-HC$_2$H$_3$O$_2$ solutions.

Our initial investigations into the application of laser micromachining
were conducted under a Collaborative Research and Development Agreement (CRDA) 
between the PI (at the University of Arizona) and Lincoln Laboratory.
One purpose of the CRDA is to transfer technology, such as the 
micromachining process described here, out of national laboratories into
the private sector. Based upon the success of this collaboration,
the Engineering Division of the National Science Foundation 
awarded the PI a grant to construct a laser micromachining system
optimized for the fabrication of THz waveguide and optical components
at Steward Observatory. This system is now fully operational.
Recently the Army Research Office awarded the PI funds for a new
laser, an e-beam evaporator for depositing gold and other metals
on the micromachined waveguide components, and a thin film deposition
system for laying down nitride layers (see below). 

\subsection{Focal Plane Array Concept}

All waveguide components
for the arrays will be micromachined out of silicon and 
assembled into an integrated package. The array design and 
fabrication can be readily scaled for use at shorter wavelengths.
A conceptual design for a $4\times 4$ array of micromachined
fixed-backshort, waveguide mixers is shown in Figure 7. The
focal plane array consists of a ``Horn Block'', ``Bolometer Block'',
and ``Backshort Block''.

\subsubsection{\it Horn Block}

The Horn Block consists of four, $1\times 4$ corrugated feedhorn
subarrays (Figure 6). Each subarray is formed by bonding two gold plated, silicon
wafers in which mirror images of the corrugated feedhorns have been
laser micromachined. Alignment between the two halves of a horn
subarray is insured by posts and corresponding holes wet-etched in
each half before laser machining. Assembly of the package
will be done with the aid of an infrared microscope and micromanipulator
system designed originally for flip-chip bonding. 

Each horn is micromachined with a circular-to-rectangular waveguide
transition (see Fig. 5) to match the input impedance of the HEB.

%Figure 5
\begin{figure}[!htb]
\centering
\begin{minipage}{7in}
\parbox{4in}{\includegraphics[scale=0.45,angle=0]{Assembly.ps}}
\parbox{2.2in}{\caption{\small Assembly Drawing of the 0.8~THz Array Mixer Block}}
\end{minipage}
\end{figure}

\subsubsection{Bolometer Block}

At high frequencies ($\ge$650~GHz) it becomes nearly impossible to manually 
mount detectors across small waveguide structures. An alternative approach 
is to fabricate the mixing elements on $\sim$1~$\mu$m thick silicon nitride membranes
which subsequently are integrated with the horn structure. To date, this 
approach has been used successfully with SIS junctions up to frequencies of 
$\sim$850~GHz [28]. As in this successful design, we will fabricate 
the mixing devices on membranes several times larger than the waveguide
aperture. These windows are formed by etching a pyramidal hole from
the backside of the silicon wafer supporting the membrane (see
Fig. 7). The original membrane mounted 850~GHz mixer worked well both 
in the lab and at the CSO. However, if during assembly, the nitride membrane 
was not made flush against the backshort block, significant signal could
be lost due to the generation of unwanted substrate modes. In the 
array design, we have reduced this effect dramatically by using a
suspended stripline rf choke design similar to that of Blundell \& Tong
and micromachining a novel rf choke structure [32] at the
Horn and Junction Block interface. With these chokes in place, more
than 1~mil (e.g. milli-inch) separation can be easily tolerated between 
the Horn, Bolometer,
and Backshort Blocks. The choke and waveguide probe designs were optimized 
[33] using Hewlett-Packard's High Frequency 
Structure Simulator (HFSS). 

\begin{figure}[!htb]
\centering
\begin{minipage}{7in}
\parbox{4.6in}{\includegraphics[scale=0.6,angle=0]{3D-C-3Pic-BW.ps}}
\parbox{1.75in}{\caption{\small Exploded view of an individual array mixer assembly.}}
\end{minipage}
\end{figure}

%The ability of the chokes to 
%contain the field in the waveguide is shown in the HFSS simulation of 
%Figure XY.

The impedance of an HEB ($\sim$50~$\Omega$) is purely resistive and does 
not vary significantly with frequency. This property allowed us to design 
a very broadband waveguide probe for use with HEBs. The widest
bandwidth was achieved using an asymmetric probe (see Figure 8a) similar 
in principle to that described by Kerr et al. [34]. Since the
probe is one-sided, the `hot' IF/bias line is folded back over the
ground plane. The IF/bias line and ground plane are isolated from
each other by a thin layer of SiO. Figure 8b shows the HFSS calculation
of the return loss ($S_{11}$) of the probe as a function of frequency.
The probe is found to work well from 700 to nearly 1100~GHz! The 
addition of an iris at the input of the feedhorn enhances the probes
performance. Such an iris is simple to implement using laser 
micromachining. If indeed this bandwidth is achieved, we would increase 
the $T_c$ of the HEBs slightly to avoid input saturation. We find
this would increase $T_m$ by only 10-20\% and require a readily
accomodated increase in LO power. 

\begin{figure}[!htb]
\centering
\includegraphics[scale=0.4,angle=0]{1Probe-C-Z.ps}
\includegraphics[scale=0.35,angle=0]{kooi9.ps}
\caption{\small HEB waveguide probe. a) 3-D CAD drawing. b) HFSS simulation of
probe return loss (S11). The plot indicates the probe should work well
from 700 to 1100~GHz.}
\end{figure}


An exploded view of an individual mixer block is shown in Figure 7. 
All waveguide components will be micromachined and gold plated 
by the Arizona group using existing facilities. The Yale group will be 
responsible for fabricating the HEB, waveguide probe, and IF output lines 
on the surface of the Bolometer Block. There is nothing in the design of 
the array that prevents it from being scaled to at least 3~THz.

The separation between mixers in the instrument focal plane
is set by the diameter of the feedhorns; 2.4~mm for the prototype
850~GHz array. Since all the mixers share a common 
Bolometer Block, crosstalk between array pixels could be a concern. 
Using HFSS, we have carefully constructed a 2x2 simulation of an array
with only $\sim$1~mm separation 
and found the crosstalk to be down below the -35~dB level across 
the band. 
%This results of the simulation are shown in Figure 13. 
The separation between array elements in the proposed
array is twice as great, suggesting crosstalk in the Bolometer
Block will not be a significant problem.

The IF output of each mixer is ultimately conveyed to wire bonding pads
on the periphery of the bolometer block by microstrip lines. 
The IF impedance of HEBs provides a good, broadband match to 50~$\Omega$ 
transmission line, so no sophisticated IF impedance transformers are required. 

\subsubsection{Backshort Block}

The fixed rectangular backshort is laser micromachined on a pyramidal
structure designed to fit the cavity behind the membrane. The
pyramidal structures can be readily made by wet-etching silicon
through an SiO mask evaporated on the wafer [35]. Once
etched, the Backshort Wafer is gold plated. With this design
the performance of the array can be optimized in the lab by trying
different backshort lengths.

\subsection{IF/Bias Distribution system}

\subsubsection{Choice of IF Frequency and Bandwidth}

Unlike the situation often encountered in conventional single pixel
and array receivers, in the proposed system it is the choice of the IF 
frequency and bandwidth that determines the size and cost of the array camera. 
In the proposed design the waveguide mixers are micromachined out of silicon
using computer controlled laser micromachining and wet etching techniques.
With this approach it costs the same to make $\sim$10 mixers as to
make just one. In both SIS and HEBs fabrication runs, typically 100's of 
devices are made at once on a single wafer. Our concept of having a
single, common bolometer block or wafer does not add significantly
to the cost or complexity of device fabrication. Since HEBs require
$\sim$30 times less LO power than SIS devices, only one commercially
available LO source (even at 810~GHz) is needed to drive the entire array.

The additional cost per pixel is driven by the cost of the 
IF components and the spectrometer needed to process the signal.
Today, 2-bit/4-level correlators are commercially available that can 
process 128 MHz of signal at 1~MHz resolution in a single chip [36].
For our design frequency of 810~GHz, these correlator chips would
provide $\sim 47$~km/s velocity coverage with a resolution of 0.37~km/s.
This bandwidth and resolution are suitable for a wide variety of
Galactic astronomy projects; from large scale mapping of molecular
clouds to searching for emission from protoplanetary disks.
A ``turn-key'' correlator system of this type can be purchased 
for as little as ~\$2K per channel, potentially making even 10$\times 10$ 
arrays tractable.

If we choose to optimize the array specifically for Galactic observations
using the 128~MHz chips, then the IF center frequency can be significantly
lower than what is generally used in receiver systems. By choosing an
IF between 500-900~MHz, one can begin to utilize the plethora of 
high quality, low-cost amplifiers and downconverters commercially produced
by the telecommunications industry. Indeed, an unpackaged low-noise,
IF amplifier with 10~dB of gain and low power dissipation can be purchased
for about $\sim$\$1! An IF downconverter to baseband (without the LO) is
available for $\sim$\$3 [MAXIM]. We are currently conducting room temperature
and crogenic tests on these devices to verify their performance. Even if 
if these devices turn-out to be inappropriate for our application, the
choice of limiting the array (initially) to Galactic astronomy (and thereby
allowing a reduced IF bandwidth and IF center frequency) will dramatically 
lower the cost of IF processing without compromising the quality of the
science that can be done. When the next generation correlator chips designed
for ALMA become available, the arrays could be upgraded to utilize
the greater bandwidth for extragalactic science.  

\subsubsection{Array Motherboard}

Running bias wires and cabling to even a small number of mixers can
be an arduous task. Bias wires are required for the mixing device
and IF amplifier. Coaxial cable must be used between the mixer,
1st IF amplifier and the outside world.
Since the mixer is typically at or below 4~K, the IF amplifier at
$\sim$15~K, and the outside world is at 290~K, the materials from
which the cables are made and how they are heat strapped are critical
to the cryogenic performance of the system. Since our goal is to develop 
the techniques for making large format arrays, we must use a different 
approach. 

We propose to make a PC `motherboard' out of Duroid (with which we have
considerable experience at cryogenic temperatures) 
for conveying bias and IF signals into and out of the focal plane array. 
A conceptual design for the motherboard is shown in Figure 9a. It is composed
of a small (1.5 x 1.5~cm) `hub' surrounded by a series of nested 
frames. Each frame operates at a temperature appropriate for
the devices it carries. In the case of the Nb HEB arrays, the 
central hub containing the array and first stage IF amplifiers 
is at 4~K. The next frame out is at 60~K and contains the 2nd stage 
IF amps. The outer frame is at 290~K and contains the PC board mounted 
SMA cable jacks.
Signals between the hub and frames are carried on interconnecting
`spokes'. We have used HP's Advanced Design System 
(ADS) software package to optimize the design of the microstrip
and DC lines on the connecting strips. These lines are very
thin ($\sim$ 3~mils wide) and are expected to have a very low thermal 
conductivity. Assuming each interconnecting strip carries
4 lines, the strips themselves need only be a few millimeters wide
to insure crosstalk between the lines is at or below the -30~dB
level. The thin, interconnecting strips will be designed with enough 
flexibility to tolerate the differential contraction between the 
frames. For the later operation with $T < 1$~K on the array stage,
Nb or NbTi thin-film lines will couple from 4~K to 1~K to reduce
the heat loading but provide high electrical conductivity.

\begin{figure}[!htb]
\centering
\includegraphics[scale=0.45,angle=0]{4x4pcboard3d-BW.ps}
\includegraphics[scale=0.40,angle=0]{4x4HeDewar-BW.ps}
\caption{\small {\bf (a)} The 4x4 focal plane array is heat strapped 
to 4~K through the central `hub' of the Array Motherboard. The 1st 
stage IF amplifiers are also
located on the hub. The 77~K second stage IF amps are on the first ring out 
from the hub. The IF connectors are on the outer 290~K ring. All IF
and bias lines run along the radial strips interconnecting the hub and
rings. The whole structure is made of a composite material that serves
both as a PC board substrate and thermal insulator.SEM close-up
of ridges. {\bf (b)} The Array Cryostat has two 4He 
cans, a LN$_2$ can, and a 3He stage. The inner 4He can is used 
to liquify the 3He. The outer 4He can cools the 1st stage IF
amps. The 3He stage will be essential for testing the Nb-Au
devices. The 2nd stage IF amps are heat sunk to the 77~K
radiation shield.}
\end{figure}

\subsection{Array Test Cryostat}

Before building the 1x4 arrays, we will conduct performance
tests on single channel versions of diffusion cooled Nb and
Nb-Au HEBs. Microwave measurements at 30-40~GHz will be done
at Yale. The 345 and 810~GHz evaluations will be conducted at Arizona.
The Nb HEBs can be tested in standard He-4 cryostats. The Nb-Au
HEBs work best at $\sim 0.5$K, and require He-3 systems. Both
Yale and Arizona already have cryostats suitable for this work.
A new, larger cryostat capable of He-3 operation will be needed for 
testing the 1x4 and 4x4 arrays. When testing the NB HEB arrays,
the He-3 stage of the cryostat need not be used. However,
by incorporating the He-3 cooling option from the start, we
avoid the cost and time of re-engineering the cryostat when
we begin testing the lower $T_c$ Nb-Au devices.

A conceptual design of the Nb HEB configuration of the 
cryostat is shown in Figure 9b. The central
hub of the motherboard contains the HEB array and the 1st
stage IF amplifiers. It is cooled to helium-4 temperatures.
The 2nd stage IF amplifier ring is attached to the 
77~K radiation shield. The 290~K ring containing the DC
bias and IF coaxial connectors is attached to the inside
wall of the the 290~K vacuum vessel. The 16 beams 
from the array first pass through an IR filter mounted on 
the lid of the 77~K radiation shield and then exits the dewar 
through an AR coated, crystalline quartz vacuum window. 
The estimated hold time of the cryostat with the array
switched on is expected to be $\geq$24~hrs, making it suitable
for both lab tests and telescope use.

%\begin{figure}[!htb]
%\centering
%\begin{minipage}{7in}
%\parbox{3.75in}{\includegraphics[scale=0.45,angle=0]{4x4pcboard3d-BW.ps}}
%\parbox{3.25in}{\caption[Array Motherboard]{\small The 4x4 focal plane array is
%heat strapped 
%to 4~K through the central `hub'. The 1st stage IF amplifiers are also
%located on the hub. The 77~K second stage IF amps are on the first ring out 
%from the hub. The IF connectors are on the outer 290~K ring. All IF
%and bias lines run along the radial strips interconnecting the hub and
%rings. The whole structure is made of a composite material that serves
%both as a PC board substrate and thermal insulator.}}
%\end{minipage}
%\end{figure}

\subsubsection{Array Bias Control System}

A computer controlled array bias control system has already
been developed by the PIs group at Arizona and is currently being
used with their 4-channel, SIS 810~GHz array (PoleSTAR) on the AST/RO
telescope at the South Pole and a 7-channel, 345~GHz SIS array (Pleiades)
soon to be installed on the HHT. The system allows manual tuning of each 
mixer and amplifier, plus automated bias point selection. 
All voltages (and currents) are controlled and monitored
through a flexible graphical user interface (GUI) written in C.
The control system is already designed to be extensible to 100 or 
more channels. For the proposed 16 channel system, the bias cards
will be modified to work specifically with HEBs. The system fits
in two standard 5" high, 19" racks.
 
\subsection{Local Oscillator}

As part of their work in constructing the PoleSTAR array, the Arizona
group successfully pumped 4 SIS mixers at 809~GHz using a single 
fixed-tuned, solid-state, 42~$\mu$W LO source together with a Martin-Puplett 
LO diplexer and a quasioptical power divider [3]. 
Diffusion cooled Nb HEBs mixers require at least an order of magnitude 
{\it less} LO power than their SIS counterparts. Therefore a single
LO source could readily pump the proposed 16 channel, HEB array.
Using a combination of HEMT power amplifiers and high efficiency
beam lead doublers, JPL has recently demonstrated a 780-820~GHz
LO source capable of delivering up to 500~$\mu$W. With this much
LO power, the 16 channel HEB array can be easily pumped using
a simple Mylar beamsplitter as a diplexer. JPL is providing
the PI with one of these high power LO sources for use on PoleSTAR. 
This will permit the array to be continually tuned from 780-
to 810~GHz and allow the Martin-Puplett diplexer to be replaced
by a simple beamsplitter. Indeed, when used to simultaneously 
pump all 4 mixers, the walk-off in the Martin-Puplett
diplexer increased receiver noise temperatures by $\approx 2$ over
what was achieved when mixers were optimized individually, 
$\sim 900$~K (Walker et al. 2001). This occurred after great
care was used in optical alignment. Clearly, the extremely low
LO requirements of HEBs is a tremendous advantage in realizing
continuously tunable, imaging arrays at THz frequencies.
 
\subsection{Array Spectrometer}

Until recently, the price and complexity of spectrometers has been
one of the major stumbling blocks to the advent large focal
plane heterodyne arrays. However, as discussed in Section 3.5, 
it is now possible to get 128~MHz of spectrometer with $\sim$1~MHz
of spectral resolution on a single correlator chip. Using this technology,
it is possible to {\it buy} a spectrometer system capable of
concurrently processing the data from a 10x10 focal plane array
for $\sim \$200$~K [36]. Driven by the ALMA project, correlator chips
with much larger bandwidth will be available in a few years.

For observing with the prototype array on the HHT, we will use an 
existing correlator
system capable of processing 16 individual 80~MHz IF inputs with a
resolution of 312.5~kHz. This corresponds to a velocity range of 
$\sim 30$~km/s and a resolution of 0.12~km/s at the array design
frequency. This velocity coverage is suitable for many Galactic
astronomy projects. The spectrometer (known as FAAS) is being provided
to the Heinrich Hertz Telescope by the University of Massachusetts
in exchange for observing time. The spectrometer will be permanently
moved to the HHT in the fall of 2001. The only spectrometer-related costs
in this proposal is for the simple, IF processor needed to match the
array's IF output to the frequency and power level required by the
correlator.

%\begin{figure}[!htb]
%\centering
%\begin{minipage}{7in}
%\parbox{4in}{\includegraphics[scale=0.4,angle=0]{4x4HeDewar-BW.ps}}
%\parbox{3in}{\caption[Array Cryostat]{\small The cryostat has two 4He 
%cans, a LN$_2$ can, and a 3He stage. The inner 4He can is used 
%to liquify the 3He. The outer 4He can cools the 1st stage IF
%amps. The 3He stage will be essential for testing the Nb-Au
%devices. The 2nd stage IF amps are heat sunk to the 77~K
%radiation shield.}}

%\end{minipage}
%\end{figure}


%\begin{figure}[!htb]
%\centering
%\begin{minipage}{7in}
%\parbox{4in}{\includegraphics[scale=0.5,angle=0]{4x4Mirrors-BW.ps}}
%\parbox{3in}{\caption[Array Reimaging Optics]{\small A pair of uncrossed,
%off-axis elliptical mirrors are used to transform the f/\#13.8 beam
%at the Nasmyth focus of the HHT to the $\sim$f/\#2.5 beam required by
%the close-packed feedhorn array.}}
%\end{minipage}
%\end{figure}

\subsection{Reimaging Optics}

The Nasmyth focal plane of the HHT ($D=10$~m f/\#13.7) must be reimaged to
match the requirements of the proposed compact, focal plane array 
($\sim$f/\#2.5). The required re-imaging optics are similar in principle to those
designed for the Submillimeter High Angular Resolution Camera (SHARC)
on the CSO [37]. The optical system, essentially a 
off axis reflective microscope, consists of two uncrossed off-axis
elliptical mirrors. Our design was entered in 
Optical Research Associates lens design program Code V and modified 
to fit space requirements particular to the HHT Nasmyth room. The
resulting design matches the array to the HHT with a predicted
96\% efficiency.
%To properly
%match both the geometrical and Gaussian beam properties of the array, the 
%aperture of the HHT must be stopped down to 9.8~m, resulting in a 96\% 
%efficiency for the whole system. 

%The internal focus between the two
%ellipsoids permits the stop to be easily implemented at a plane 
%conjugate of the primary mirror.

\section{Observing Time on the HHT}

Steward Observatory will make two weeks of time available for field
testing SuperCam hardware on the HHT during each of the 3 years
of the project. Once it has been commissioned, SuperCam will be
available to all observers. Over
the past several years, $\sim$30\% of all Steward HHT time has been awarded
to non-Arizona groups. To make the most efficient use of periods of very low
atmospheric opacity, priority observing is in place at the HHT. When the 
opacity reaches $\tau_{225~GHz} \leq 0.05$, high frequency programs (such as
those that will use SuperCam) are automatically switched in.

\section{Production of Devices for Collaborators}

We plan also to produce individual HEB devices and/or micromachined
components for use in systems by other investigators. See for example, the
attached letters from Zimuidzinas and Blake at Caltech, Stark
at the Center for Astrophysics, and Betz at UC Boulder. Our goal is to make 
this new technology available for use by the larger community.

\section {Educational Impact of Proposed Research}

\subsection{University of Arizona}

Almost all the instrumentation designed and fabricated in 
the Steward Observatory Radio Astronomy Lab (SORAL) was done 
by students under the supervision of the PI. Past Ph.D. grads
from the lab include Jason Glenn (now a faculty member at
U.C. Boulder) and Gopal Narayanan (faculty member at U. Mass.).
Currently, there are 4 grad students and 3 undergrads 
working in the lab on a wide range of instrumentation projects. 
When appropriate, the students use the instruments they 
have built toward their undergraduate or graduate degrees.
Even though the salary of only one Arizona grad student is requested
in the proposal, all the students will benefit from the project.

The PI is now in the process of organizing an `Astro-Technology'
initiative at the University of Arizona. The goal is to build
a cross-disciplinary program that would facilitate
the exchange of faculty members, postdocs, students, ideas,
and physical resources between departments (e.g.
Astronomy, Planetary Sciences, Optical Sciences, and Electrical
Engineering) interested in applying leading-edge technology to the
solution of astrophysical problems. The proposed instrument will
serve as a model for this initiative, illustrating how diverse 
technologies can be fused to provide a new, powerful instrument 
for observational astronomy.

\subsection{Yale}

In D. Prober's laboratory at Yale, there are typically one or two 
undergraduates at any time working on projects.  In the past 5 years, 
4 students have done year-long senior projects, and all of these 
students have gone on to Ph.D. programs in Physics or Applied 
Physics.  A senior undergrad is doing his project with I. Siddiqi 
this year, and will present his results at a THz conference this 
fall, and also submit them for publication, likely as the first 
author.   Yale undergraduate majors are well equipped to contribute 
to, and benefit from, these research experiences.

The two graduate students who have worked on HEB mixers, Peter Burke 
and Irfan Siddiqi, have both done outstanding work.  Siddiqi will 
finish his Ph.D. in the coming academic year.  Burke won a Millikan 
Postdoctoral Fellowship at Caltech in 1997.  A postdoc who previously 
worked on the HEB program, Robert Schoelkopf, is now a faculty member 
at Yale in Applied Physics with his own research group.

\section {Results from Prior NSF Support}

\subsection{PI: Christopher K. Walker}

\noindent
A NSF Young Investigator Award AST-9457445 was made to 
the PI for the period 7/1/94 - 7/1/99
of \$62,500 per year (matching funds have been obtained for all 
5 years). This award was used to support research and teaching
efforts. Research included further development of the laser 
micromachining waveguide technology, the construction of submillimeter
receiver systems at 230 and 490~GHz for the Arizona/MPIfR
Submillimeter Observatory, a 492/810~GHz receiver system
for the AST/RO telescope at the South Pole, the funding
of graduate and undergraduate students for the study of protostellar evolution,
and the construction of a submillimeter polarimeter and student radiotelescope. 

A grant (AST-9622569) from the NSF ATI program was made to the PI
to construct an 870 micron Array Receiver for the Heinrich Hertz Telescope.
The award period was from 8/1/96 - 7/31/99 for a total of \$380,931. 
The array consists of 7 hexagonally packed receiver channels housed in 
a closed-cycle cryostat. The array will go into operation on the
HHT in November 2001. It will be the first array receiver to 
operate in the 870 micron atmospheric window.

An award (ECS-9800260) from the NSF Physical Foundations of 
Enabling Technologies Program was made to the PI  
to construct and utilize a laser micromachining system at the 
University of Arizona. The award period was from 6/1/98 - 5/31/00 
for a total of \$280,000. The system is fully operational 
and will be used in the proposed research effort.

\subsection{Co-PI: Daniel Prober}

	The concept of using diffusion cooling to provide large 
bandwidth for a thermal mixer was proposed by the co-PI, D. Prober, 
in 1993, and the noise theory delineated.  Research was soon 
initiated with JPL to prove this concept, with the Yale group 
conducting low frequency mixing tests of Nb HEBs fabricated at JPL. 
The JPL group of McGrath et al. tested HEBs at submillimeter and then 
THz frequencies.   The Yale group established the bandwidth 
predictions as a function of device length using microwave mixer studies, 
and also that the noise bandwidth was determined by the thermal relaxation time.  
The JPL group demonstrated low noise mixing at 0.5, 0.6, 1.2 and 2.5 THz.

Recently, the two groups have studied aluminum (Al) HEBs to achieve 
the goal of lower noise.  This goal proved out, but the devices were 
so sensitive that they were easily saturated at the output in real 
THz conditions.  This disqualified Al as an HEB material, but 
encouraged testing of other materials with $T_c$ lower than the Nb HEBs, 
but not having the very long coherence length of Al.

The Yale group has recently  tested Nb HEBs in a magentic field, 
which reduces $T_c$.  The performance approaches that of Al, but without 
the large saturation problems, which were understood from simulations 
to result in part from the very long coherence length of Al.  Most 
recently the Yale group has itself fabricated with electron-beam 
lithography Nb-Au HEBs, and tested these at microwave frequencies. 
These are even substantially better than Nb HEBs in a magnetic field 
with the same $T_c$.  The Nb-Au HEBs now are proven to be outstanding 
candidates for the most sensitive heterodyne mixer elements above 1 
THz, and ideal candidates for arrays.

\section{Plan of Action}

The following is a brief outline/sketch of some of the tasks to be 
accomplished and our expectation as to when each will occur. 

\begin{table}[!hbt]
\centering
\begin{tabular}{|c|c|}
\hline
{\bf Yale} & {\bf Arizona} \\
\hline 

\parbox{3.0in}{{\flushleft {\it $\triangleleft$ Year 1 $\triangleright$}} \medskip \\ \\ $\bullet$ Fabricate Nb HEBs on quartz substrates for testing
   in existing 345 \& 810~GHz waveguide systems. \smallskip \\ 
$\bullet$ Refine fabrication of Nb HEBs on SiN
substrate. (Nb SIS mixers on SiN have already been tested and used
successfully in receiver systems. See work of PI with J. Kooi and
collaborators in Kooi et al. 1998) \smallskip \\ 
$\bullet$ Fabricate prototype 1x4 Nb HEB arrays on SiN.} 

&

\parbox{3.0in}{$\bullet$ Procure array cryostat. \smallskip \\ 
$\bullet$ Test single 345 and 810 GHz Nb HEBs in existing waveguide
mixer blocks and cryostats. \smallskip \\ 
$\bullet$ Test, identify low-noise IF amps. \smallskip \\ 
$\bullet$ Design cryogenic DC bias/IF motherboard for use
in array cryostat. \smallskip \\ 
$\bullet$ Design and build IF processor to link the array
to the existing correlator system. \smallskip \\ 
$\bullet$ Configure array cryostat for testing Nb HEB
mixer array and test prototype of 1x4 Nb HEB mixer array in lab using
borrowed 810~GHz LO.}  \\ 


\hline
\parbox{3.0in}{\flushleft{\it $\triangleleft$ Year 2 $\triangleright$}} & \\

\parbox{3.0in}{$\bullet$ Fabricate Nb/Au HEBs on quartz substrates for 
   testing in existing 345 \& 810 GHz mixer blocks, in existing $^3$He
system. \smallskip \\
$\bullet$ Produce single Nb/Au HEBs on SiN for 810~GHz
tests. \smallskip \\
$\bullet$ Develop HEB bias 'board' on single card and test at Yale and
Arizona. \smallskip \\
$\bullet$ Develop and test Nb IF wiring to be used for coupling to Nb-Au 
HEBs on 3He stage of array cryostat.}
&
\parbox{3.0in}{$\bullet$ Purchase 810 GHz LO for array. \smallskip \\
$\bullet$ Once the 4x4 Nb HEB mixer array has been successfully
   characterized in the lab, configure it for use on the
   Heinrich Hertz Telescope (HHT). \smallskip \\
$\bullet$ Fabricate HHT reimaging optics for use with array \smallskip
\\
$\bullet$ Use the Nb HEB array for astrophysical studies on the
HHT. \smallskip \\
$\bullet$ Wire existing (small) $^3$He cryostat for testing single Nb-Au
HEBs; perform tests on single Nb-Au HEBs in $^3$He cryostat.} \\


\hline
\parbox{3.0in}{\flushleft{\it $\triangleleft$ Year 3 $\triangleright$ }} & \\


\parbox{3.0in}{$\bullet$ Test 1x4, Nb-Au HEB array at 40 GHz. \smallskip
\\
$\bullet$ Fabricate 1x4, Nb-Au array for 810 GHz. \smallskip \\
$\bullet$ Deliver 1x4, Nb-Au array to Arizona. \smallskip \\
$\bullet$ Expand 1x4 Nb-Au array to 4x4 format when ready. }
&
\parbox{3.0in}{$\bullet$ Test thermal and electrical elements of array
cryostat for Nb-Au, $4\times 4$ array. \smallskip \\
$\bullet$ Perform lab tests of Nb-Au, 1x4 array in array
cryostat. \smallskip \\
$\bullet$ Expand to 4x4 array as soon as practical. \smallskip \\
$\bullet$ Prepare Nb-Au array for use on the HHT. } \\

\hline
\end{tabular}
\end{table}





\vfill
\eject
\end{document}


\section{\bf REFERENCES CITED}

\begin{enumerate}
\setlength{\itemsep}{-0.8ex}
\setlength{\parsep}{-0.8ex}

\item [0] Boonman, A.~M.~S., Stark, R., van der Tak, F.~F.~S., van
Dishoeck, E.~F., van der Wal, P.~B., Sch{\" a}fer, F., de Lange, G.,
\& Laauwen, W.~M.\ 2001, ApJL, 553, L63 

\item [0] Wilson, T.~L., Muders, D., Kramer, C., \& Henkel, C.\ 2001,
ApJ, 557, 240

\item [0] Ceccarelli, C., Hollenbach, D.~J., \& Tielens, A.~G.~G.~M.\
1996, ApJ, 471, 400

\item [0] Ceccarelli, C.~et al.\ 1998, A\&A, 331, 372

\item [0] Dame, T.~M., Hartmann, D., \& Thaddeus, P.\ 2001, ApJ, 547, 792

\item [0] Stark, A.~A.~et al.\ 2001, PASP, 113, 567

\item [0] Kaufman, M.~J., Wolfire, M.~G., Hollenbach, D.~J., \&
Luhman, M.~L.\ 1999, ApJ, 527, 795

\item [0] Howe, J.~E.~et al.\ 2000, ApJL, 539, L137

\item [0] Kawamura, J.~et al.\ 2001, in preparation


Bieging, J.H., Wilner, D., and Thronson, H.A. 1991, ApJ, 379, 271

Latter, W.B., Dayal, A., Bieging, J.H., et al. 2000, ApJ, 539, 783

Young, K., Cox, P., Huggins, P.J., Forveille, T., and Bachiller, 
R. 1999, ApJ, 522, 387



\item [1] J. Kooi, J. Pety, B. Bumble, C. Walker, H. LeDuc, P. L.
Schaffer, and T.G. Phillips, 1998, ``An 850~GHz waveguide receiver
employing a niobium SIS junction fabricated on a 1~$\mu$m Si$_3$N$_4$
membrane'', IEEE MMT, vol. 46, pp. 151-161.

\item [2] J. Kooi, C. K. Walker, H. G. LeDuc, T. R. Hunter, D. J. Benford,
and T. G. Phillips, 1994, ``A low noise 665~GHz SIS quasi-particle
waveguide receiver'', Int. J. of IR and MM Waves, vol. 15, no. 3, pp. 477-492.

\item [3] C. K. Walker, J. Kooi, M. Chan, H. G. LeDuc, P. L. Schaffer, 
J. E. Carlstrom, and T. G. Phillips, 1992, ``A low noise 492~GHz SIS 
waveguide receiver'', Int. J. of IR and MM Waves, vol. 15, 
no. 3, pp. 477-492.

\item [4] K. Farooqui, J. Gundersen, P. Timbie, G. Wilson, J. Zhou,
C. Allen, T. Chen, H. Moseley, and B. Mott, 1997, ``The single-mode
monolithic silicon bolometer as an ultrasensitive detector for millimeter
wavelengths'', 
8th International Symposium on Space Terahertz Technology, eds. Blundell
and Tong, Harvard University, p. 546.

\item [5] W. Ali-Ahmad and G. M. Rebeiz, 1991, ``92~GHz Dual-Polarization
Integrated Horn Antennas'', IEEE Trans. on Antennas and Prop., vol. 39,
no. 6, pp. 820-825.

\item [6] G. Rebeiz, G. W. Regehr, G. Wade, D. B. Rutledge, R. L. Savage,
L. Richard, N. C. Luhmann JR, Int. J. of IR and MM Waves, vol. 8, 
1249, 1987.

\item [7] R. McGrath, C. K. Walker, M. Yap, and Y. Tai, 
IEEE Microwave and Guided Wave Letters, vol 3, 61, 1993.

\item [8] C.K. Walker, T.M. Bloomstein, G. Narayanan, et al., 1997,
  8th International Symposium on Space Terahertz Technology, eds. Blundell
  and Tong, Harvard University.

\item [9] D.J. Ehrlich, R.M. Osgood, Jr., and T.F. Deutsch,
Appl. Phys. Lett.,  38, 1018, 1981.

\item [10] G.V. Treyz, R. Beach, and R.M. Osgood, Jr.,  J. Vac. Sci. Technol.
B. 6, 37, 1988.

\item [11] G.V. Treyz, R. Beach, and R.M. Osgood, Jr.,
Appl. Phys. Letters 50, 475, 1987.

\item [12] T.M. Bloomstein and D.J. Ehrlich, in Technical Digest of
Transducers (IEEE, New York, 1992), pp. 507-511, 1991.

\item [13] T.M. Bloomstein and D.J. Ehrlich, ``Stereo laser
micromachining of silicon'', Appl. Phys. Lett. 61, 708,
1992.

\item [14] Y.S. Liu, "Sources, optics, and laser microfabrication
systems for direct writing and projection lithography" in Laser
Microfabrication, edited by D.J. Ehrlich and J.Y. Tsao (Academic
Press, San Diego, ch. 1., 1989.

\item [15] See M3 Scanner/Driver User's Manual, Rev. A (General Scanning, Inc.
Watertown, MA, 1992).

\item [16] T.M. Bloomstein, Sc.D. Thesis, Massachusetts Institute of 
Technology, 1996.

\item [17] E. Kim, Y. Xia, and G.M. Whitesides, Nature 376, 581, 1985.

\item [18] Sahr, M., Honingh, C.E, Haas, S., Jacobs, K., 9th 
International Symposium on Space Terahertz Technology

\item [19] Sahr, M., Honingh, C.E., Haas, S., Hottgenroth, D.,
Jacobs, K. ''Low noise fixed tuned 490 GHz SIS mixers made of
epoxy resin'', to appear in Int. J. IR MM waves, 1999 
     
\item [20] A.G.G.M. Tielens, 1995, Airborne Astronomy Symposium, 73, 3.

\item [21] S. Paine, 1999, ``FTS Measurements of Submillimeter
Atmospheric Transmission at Chajnantor, Chile'',  National Radio Science
Meeting (URSI), Boulder, CO, Jan.

\item [22] H. Matsuo and S. Matsushita, 1999, ``FTS Measurements of 
Submillimeter-Wave Atmospheric Opacity at Pampa La Bola'',  
National Radio Science Meeting (URSI), Boulder, CO, Jan. 

\item [23] G de Lang, A. Rahman, E. Duer, Q. Hu, H. Huang and A.W. 
Lichtenberger,
``Development of a 3x3 Micromachined Millimeter Wave SIS Imaging Array''
IEEE Transactions on Applied Superconductivity,
1996.                                                   

\item [24]
G de Lang, Q.Hu, H.Huang and A.W. Lichtenberger, ``Development of a
170-210 GHz Micromachined SIS Imaging Array'' Proceedings of the Eight
International Symposium on Space Technology, 1997.  

\item [25]
A. Datesman and A.W. Lichtenberger, ``Focussed Ion Beam Fabrication
of Nb based Hot Electron Bolometers'',
to appear in the IEEE Transactions on Applied Superconductivity, June 1999. 

\item [26]
A. Datesman, A.W. Lichtenberger, ``Fabrication of Ultra-Small
Hot-Electron Bolometers with a New Focused Ion Beam Fabrication
Technique'', Accepted for the 4th International Conference on Millimeter
and Submillimeter Waves and Applications, 1998.

\item [27]
A. Datesman, A.W. Lichtenberger, "A New Fabrication Technique for
Nb  Diffusion-Cooled Hot-Electron Bolometers", 1997 International
Semiconductor Device Research Symposium Proceedings, December 1997.
         
\item [28] Infrared Laboratories Inc., 1808 E 17th St., Tucson, Az.

\item [29] N. Erickson, 1997, 8th International Symposium on Space 
    Terahertz Technology, eds. Blundell and Tong, Harvard University.

\item [30] G. F. Delgado and Bengtsson, 1194, Microwave and Optical 
Technology Letters, vol. 7, No. 18, pp. 831-834.

\item [31] T. Klein, G. A. Ediss, R. G\"usten, C. Kasemann, 1997,
   8th International Symposium on Space Terahertz Technology, eds. Blundell
  and Tong, Harvard University.

\item [32] Genn, J., 1998, private communication.


\end{enumerate}
\vfill
\eject
\end{document}







\section{\bf FACILITIES, EQUIPMENT \& OTHER RESOURCES}
\subsection{\it University of Arizona}

Steward Observatory, in
association with the Max Planck Institute for Radioastronomy, has 
constructed a 10~m submillimeter telescope
on Mt. Graham, Arizona (the Heinrich Hertz Telescope, HHT). In support
of this 8 million dollar investment, we have established a laboratory 
(the Steward Observatory Radio Astronomy Laboratory, SORAL) for
the development of state-of-the-art submillimeter-wave receiver systems.
The laboratory contains or has ready access to all the equipment 
(spectrum analyzers, network analyzer's, vacuum pumps, cryogenic
support facilities, etc.) needed for the development of receivers.  
The NSF Division of Astronomical Sciences has previously awarded
the PI funds to construct a 7 element array receiver at 345~GHz. 
The laser micromachined mixer arrays will be evaluated using many
of the facilities developed in support of the 345~GHz array.
In the past, SORAL has produced facility 230 and 492~GHz receivers
for the HHT and, recently, was the lead group in the design and
construction of a dual channel 492/810~GHz receiver for AST/RO at
the South Pole. These receiver systems are now in daily use at each
of these observatories. The experience SORAL personnel have gained in 
the design and deployment of these receiver systems will be fully 
utilized in the construction of the proposed prototype systems.

As a result of its successful collaboration with Lincoln Laboratory
in applying laser micromachining technology to the fabrication
of THz components, the Physical Foundations of Enabling Technologies
Program in the Engineering Division of the NSF recently awarded the PI 
a grant to construct a laser micromachining facility at Steward Observatory.
The design of this facility is based on the successful Lincoln
Laboratory system and optimized for the THz applications described
in this proposal. The availability of a state-of-the-art laser micromachining
system at Steward Observatory provides the community with a {\it powerful,
new} ability to develop a wide variety of needed THz components. 
Photolithographic facilities are also available at Steward for fabricating 
the wet-etched portions of the focal plane arrays.

SORAL also has licenses for
both Hewlett Packard's High Frequency Structure Simulator (HFSS) and
Microwave Design System (MDS) software packages. These programs
are used to accurately model and optimize mixers and other
crucial receiver components. 

\section{\bf CURRICULUM VITAE}
\vfill
\eject

\section{\bf CURRENT \& PENDING SUPPORT OF PI}
\subsection{\it Pending Awards}

\noindent
Title: {\it Micromachining of TeraHertz Waveguide and Quasi-Optical
Components for Suborbital and Space-Borne Detctors}, (this proposal), 
\noindent
Agency: NASA: NRA 99-SPA-01, 
\noindent
Budget: \$457,465 from 12/1/1999 to 11/31/02, 
\noindent
Commitment: 1 month/yr

\medskip
\noindent
Title: {\it Micromachining of TeraHertz Waveguide and Quasi-Optical
Components for SOFIA, FIRST, and TPF}, 
\noindent
Agency: NASA: NRA 98-OSS-10, 
\noindent
Budget: \$332,043 from 5/1/1999 to 4/30/01, 
\noindent
Commitment: 1 month/yr

\subsection{\it Current Awards}

\noindent
Title: {\it Laser Micromachining of Silicon: A New Technology for
Fabricating THz Imaging Arrays}, 
\noindent
Agency: NSF, 
\noindent
Budget: \$280,000 from 5/1/1998 to 4/30/01, 
\noindent
Commitment: 1 month/yr

\medskip
\noindent
Title: {\it NSF Young Investigator Award}, 
Agency: NSF, 
\noindent
Budget: \$312,500 from 7/1/94 to 6/30/99, 
\noindent
Commitment: 1 month/yr

\medskip
\noindent
Title: {\it An 870~$\mu$m Array Receiver for 
the Arizona/MPIfR Submillimeter Telescope}, 
\noindent
Agency: NSF, 
\noindent
Budget: \$390,931 from 8/1/1996 to 7/31/99, 
\noindent
Commitment: 1 month/yr

\medskip
\noindent
Title: {\it An 810~GHz Array Receiver for 
AST/RO}, 
\noindent
Agency: Smithsonian Astrophysical Observatory, 
\noindent
Budget: \$99,500 from 5/21/1997 to 6/30/99, 
\noindent
Commitment: 1 month/yr
\vfill
\eject
\section{\bf CO-I AND COLLABORATOR LETTERS of COMMITMENT}




\vfill
\eject

\section{\bf BUDGET SUMMARY}
\vfill
\eject

\section{\bf BUDGET DETAILS}

The proposed effort uses leading-edge technology in 
micromachining, laser LO's, and array AOSs to achieve its goals. 
The construction of the laser micromachining system is being
funded by the NSF. The laser LO and array AOS have been financed 
through SBIR grants. Together, there is $>$ \$1.3M of hardware
and labor that have been expended in setting-up these systems.
UVa has one of the best HEB fabrication
facilities and is willing to make it available
to us at a relatively modest cost. AST/RO already has the
IF processors and backend spectrometer to support a 4 element
array. In this proposal we are 
asking for funds to utilize the power of these facilities 
to build proof-of-concept heterodyne arrays for the first
time at THz frequencies. 

\subsection{\it Year 1}

During the first year of funding we will begin laser micromachining
the $1\times 4$ subarrays at 1.5 and 2.5~THz. We will also
begin assembling the components of the 4-channel receiver 
`testbed' into an integrated system. The components include
the cryostat, GSFC laser LO and array AOS, bias control electronics,
and antenna test chamber. Here we request funds for the salary
and components the PI and a graduate student will need to conduct 
this work. UVa will have their first production runs of HEB 
devices under their subcontract. Funds are requested to cover travel, publications, and communications charges associated with the project.

\subsection{\it Year 2}

In the second year, we will conduct performance tests on the 
1.5 and 2.5~THz arrays and continue to optimize their performance. 
A 1.5~THz subarray will be packaged in an AST/RO cryostat for
field testing at the South Pole. All components needed to field
test the array are being purchased by the AST/RO project.
Funds are requested to
pay for the PI's and graduate student's work in support of this
proposal. Funds are also needed to replace expendible materials
used in the array fabrication. UVA will continue to make HEB
devices under their subcontract. A modest amount of funds are
requested to cover costs associated with travel, publications, and 
communications (telephone, FAX, connection fees).

\subsection{\it Year 3}

In the third year, we will assemble $4\times 4$ arrrays at
1.5 and 2.5~THz from optimized $1\times 4$ subarrays and evaluate 
their performance. Funds are requested to
pay for the PI's and graduate student's work during this period. 
Funds are also needed to replace expendible materials
used in the array fabrication. UVA will continue to make HEB
devices under their subcontract. A modest amount of funds are
requested to cover costs associated with travel, publications, and 
communications (telephone, FAX, connection fees).

\vfill
\eject

\end{document}



F. Budget

                 
                  Arizona Itemized Budget
                        Year 1 
	
     Personnel    
         Salaries: 	
          1)PI (1 mo)              7,054
          2)Grad Student          26,718
            (12 months)
 	
         Fringe:
          1)19.6%                  1383
          2) 4.0% 	           1069
                                           36,224
         Travel:
          Trip to Yale
          airfare x2                800
          hotel (2 nights) x2       360    
                                            1,060
     Operations      
          Communications:
          Computer services        1000
          phone, postage,           500
          photocopying
                                         
         Materials:
          etching chemicals         890
          glassware                 500
          cryogens                 2000
                                           4,890	
     Fabricated Equipment
        machining                  3000   
        low-noise IF amplifiers    8000
         (parts, PC boards, 
           power supplies)
        IF processor               8000
        clean room fees            2000           
                                          21,000     
     Indirect Cost 
        51.5% of $63,174 base             32,535

     Capital Equipment
        810 GHz Local Oscillator          50,000                                         
  		 
  				  Total: $145,708    


                 
                Arizona Itemized Budget 
                       Year 2

	
     Personnel    
         Salaries: 	
          1)PI (1 mo)              7,336
          2)Grad Student          27,787
            (12 months)
 	
         Fringe:
          1)19.6%                  1438
          2) 4.0% 	           1112
                                           36,673
         Travel:
          Trip to Yale
          airfare x2                800
          hotel (2 nights) x2       360    
          
          Trips to HHT          
          truck rental  x2          500           
          
                                           1,660      
     Operations      
          Communications:
          Computer services        1000
          phone, postage,           500
          photocopying
                                         
         Materials:
          etching chemicals         890
          glassware                 500
          cryogens                 2000
                                           4,890	
     Fabricated Equipment
        machining                  3000
         (telescope mount, etc.)     
        reimaging optics           8000
         (mirrors, lenses)                 
                                          11,000     
     Indirect Cost 
        51.5% of $54,223 base             27,925

     Capital Equipment
        He3 Cryostat                      60,000                                         
  		 
  				  Total: $142,148    
	  

                 
                  Arizona Itemized Budget 
                         Year 3
	
     Personnel    
         Salaries: 	
          1)PI (1 mo)              7,629
          2)Grad Student          28,898
            (12 months)
 	
         Fringe:
          1)19.6%                  1496
          2) 4.0% 	           1156
                                           38,140
         Travel:
          Trip to Yale
          airfare x2                800
          hotel (2 nights) x2       360    
          
          Trips to HHT          
          truck rental  x2          500           
          
                                           1,660      
     Operations      
          Communications:
          Computer services        1000
          phone, postage,           500
          photocopying
                                         
         Materials:
          etching chemicals         890
          glassware                 500
          cryogens                 2000
                                           4,890	
     Fabricated Equipment
        IF board for low-$T_c$ array  1000         
                                           1,000     
     Indirect Cost 
        51.5% of $45,690 base             23,530

                                		 
  				  Total: $69,220    
	  
	       
        


	  
%\item Continue astrophysical studies with Nb HEB array on HHT
   until Nb-Au array is delivered.

Funds
from the award were also used to construct an 
on-campus student radio telescope for instructional purposes,
purchase of a CCD camera for the on-campus optical
telescope, the purchase of computers for student use, 
salaries for undergraduate researchers, and to purchase materials
for a new undergraduate course on `Life in the Universe' taught
by the PI. 


The system uses a focused argon-ion laser beam to `mill' 3-D
structures in silicon. The system has many potential uses.
The main application of this technology at Arizona is the fabrication
of large format heterodyne array receivers for submm astronomy.
