A 1-THz Superconducting Hot-Electron-Bolometer Receiver for ...

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IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 52, NO. 10, OCTOBER 2004

A 1-THz Superconducting Hot-Electron-Bolometer Receiver for Astronomical Observations Denis V. Meledin, Daniel P. Marrone, C.-Y. Edward Tong, Member, IEEE, Hugh Gibson, Raymond Blundell, Scott N. Paine, Member, IEEE, D. Cosmo Papa, Michael Smith, Todd R. Hunter, James Battat, Boris Voronov, and Gregory Gol’tsman

Abstract—In this paper, we describe a superconducting hot-electron-bolometer mixer receiver developed to operate in atmospheric windows between 800–1300 GHz. The receiver uses a waveguide mixer element made of 3–4-nm-thick NbN film deposited over crystalline quartz. This mixer yields double-sideband receiver noise temperatures of 1000 K at around 1.0 THz, and 1600 K at 1.26 THz, at an IF of 3.0 GHz. The receiver was successfully tested in the laboratory using a gas cell as a spectral line test source. It is now in use on the Smithsonian Astrophysical Observatory terahertz test telescope in northern Chile. Index Terms—Hot-electron-bolometer (HEB) submillimeter-wave technology, terahertz astronomy.

mixers,

I. INTRODUCTION

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PECTRAL LINE emission from numerous important atoms and molecules, including water, carbon, carbon monoxide (CO), and nitrogen can be observed in the terahertz frequency region, especially between 0.3–2.5 THz [1]. Nevertheless, the universe is largely unexplored between 1–5 THz because the Earth’s atmosphere is almost completely opaque. Recent atmospheric measurements, however, have confirmed that several windows can open up between 1–3 THz at very high dry locations [2], [3]. Furthermore, three windows, centered at 1.03, 1.35, and 1.5 THz, show transmission as high as 40% under favorable conditions. These windows contain a number of rotational transitions of carbon monoxide, an abundant tracer of cool molecular gas in the galaxy, along with the ground state transition of singly ionized atomic nitrogen, and numerous other common and exotic molecular species. Immediate interest now exists in the scientific community to perform heterodyne observations at terahertz frequencies from

Manuscript received March 3, 2003. The work of D. P. Marrone was supported by the National Science Foundation under a Graduate Research Fellowship. The work of J. Battat was supported under a National Defense Science and Engineering Graduate Student Research Fellowship. D. V. Meledin was with the Harvard–Smithsonian Center for Astrophysics, Cambridge, MA 02138 USA. He is now with the Advanced Receiver Development Group, Onsala Space Observatory, SE-439 92 Onsala, Sweden. D. P. Marrone, C.-Y. E. Tong, R. Blundell, S. N. Paine, D. C. Papa, M. Smith, T. R. Hunter, and J. Battat are with the Harvard–Smithsonian Center for Astrophysics, Cambridge, MA 02138 USA (e-mail: dmarrone@ cfa.harvard.edu). H. Gibson was with the Harvard–Smithsonian Center for Astrophysics, Cambridge, MA 02138 USA. He is now with RPG Radiometer Physics GmbH, 53340 Meckenheim, Germany. B. Voronov is with the Processing Laboratory, Moscow State Pedagogical University, Moscow 119891, Russia. G. Gol’tsman is with the Physics Department, Moscow State Pedagogical University, Moscow 119891, Russia. Digital Object Identifier 10.1109/TMTT.2004.835979

the ground, along with observations from air- and space-borne platforms currently under development. A terahertz test telescope, the Receiver Laboratory Telescope (RLT), has been designed and assembled at the Harvard–Smithsonian Center for Astrophysics, Cambridge, MA, as a pioneering instrument for terahertz radio astronomy. In this paper, we present the receiver system currently employed at the RLT, which has been in operation in northern Chile since November 2002. II. HOT-ELECTRON-BOLOMETER (HEB) MIXER Superconductor–insulator–superconductor (SIS) mixers are widely used in ultra-low noise heterodyne receiver systems at frequencies up to 1 THz [4]. However, SIS mixers have a natural frequency limit at approximately twice the superconducting energy gap. For Nb- and NbTiN-based SIS mixers, the high-frequency limit for low-noise operation is approximately 1.2 THz [5]. Like the SIS mixer, the HEB mixer has a low local oscillator (LO) power requirement. However, it is much simpler to fabricate and has now become the mixer element of choice for low-noise receiver design at frequencies in excess of 1 THz. Submicrometer-sized HEB mixers can operate at very high speeds through either fast diffusion or phonon cooling. In diffusion cooled HEB mixers, electron energy diffuses from very short mixer elements, made of clear superconducting film with a large electron diffusion constant, to normal contact pads [6]. In phonon-cooled devices, the electron energy relaxes through interaction with phonons that escape from the film to the substrate [7]. The speed of the mixer is determined by the electron–phonon interaction time, as well as the acoustic reflectance of the film–substrate interface. A number of groups have reported on HEB mixers developed for terahertz applications. Currently, the best reported doublesideband (DSB) receiver noise temperatures for receivers incorporating planar antenna NbN mixers are 12–15 times the quantum limit: 450 K at 600 GHz [8], 800 K at 1.1 THz [9]. Waveguide NbN HEB mixer receivers have shown similar DSB receiver noise temperatures: close to 1000 K at 1.035 THz and 1300 K at 1.267 THz [10]–[12]. III. INSTRUMENT DESIGN The receiver design accommodates both practical and astronomical constraints. The IF bandwidth was set to 1 GHz to allow wide-band observations of spectral lines, which, for extragalactic sources, may be several hundred megahertz wide.

0018-9480/04$20.00 © 2004 IEEE

MELEDIN et al.: 1-THz SUPERCONDUCTING HEB RECEIVER FOR ASTRONOMICAL OBSERVATIONS

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To take advantage of the atmospheric windows and the readily observable CO lines, the receiver was designed to cover the 1.03-THz window and part of the 1.3-THz window. Due to the high atmospheric opacity, even at the highest driest sites available for astronomical observation, special care was taken to minimize instrument losses. The optics, including LO and receiver alignment, were designed for optimal coupling, and we have employed a waveguide mixer equipped with a corrugated feed horn for good antenna coupling efficiency. A. HEB Mixer Elements At the heart of our heterodyne receiver is a phonon-cooled HEB waveguide mixer based on an NbN thin film. The use of an ultra-thin NbN film deposited on a silicon or magnesium–oxide (MgO) substrate has been shown to give an IF bandwidth of up to 5 GHz for planar antenna mixer designs [13]. However, for our waveguide-based mixers, quartz is the most common substrate due to its low dielectric constant and the ease of processing and handling. We have reported on the use of an MgO buffer layer to improve the acoustic match between the NbN film and quartz substrate [10] and have found that the IF bandwidth can be increased to 3.5 GHz for devices fabricated on an MgO buffer layer. The mixer elements in this receiver are made from high purity 3.5-nm-thick ( 0.5) NbN films deposited on a 100- m-thick -cut crystalline quartz substrate using reactive magnetron sputtering in an argon–nitrogen gas mixture. During sputtering, the partial pressure of the two gases are kept at 5 10 mbar 10 mbar, respectively. With a discharge current and 9 and voltage of 300 mA and 300 V, we obtain a sputtering rate of 0.5 nm/s so the thin films are typically deposited in approximately 10 s. During deposition, the substrate is heated to 830 C. For these films, we typically measure critical temperatures of approximately 8–9 K and transition widths of between 0.6–0.8 K. The films are patterned using both optical and e-beam lithography to form 2- m-wide single bolometric elements. The 150-nm-long mixer element is formed across two overlaid Au–Ti electrodes, which also couple the mixer to the waveguide. With these dimensions, the mixer’s room-temperature resistance is approximately 120–180 . The is approximately 15% higher than normal-state resistance the room-temperature value. After fabrication, the wafer is diced into small blocks, approximately 5-mm square, which are then lapped and polished to a thickness of 23 m. The blocks are further diced into individual mixer chips 90 m 1.4 mm, which fit into a suspended microstrip channel across a reduced-height waveguide mixer block. The mixer, designed at the Harvard–Smithsonian Center for Astrophysics, is made in two sections [12]. The front section carries the integrated corrugated feed horn, which is electroformed and then soldered into a copper block. The back section houses a shorted section of waveguide, i.e., 50 m deep. This length was chosen to provide a good input match to the mixer element over the entire signal frequency band. For this study, we have used a mixer element with a room-temperature resistance of 170 and critical current of 130 A at a 4.2-K bath temperature.

Fig. 1. Schematic of the receiver optics. The (1) cryostat contains a (1a) paraboloidal mirror and the (1b) mixer block. (2) The Martin Puplett diplexer consists of roof mirrors and a polarizing wire grid, and combines power from the (3) LO unit with the (4) incoming signal from the telescope.

B. Receiver System Referring to Fig. 1, we use a Martin Puplett polarizing interferometer (MPI) to couple LO power and the signal from the telescope to the mixer. In this way, we efficiently couple the signal and LO to the mixer, and take full advantage of the bandwidth of available low-power solid-state LO sources. A series of Gunn oscillators and Schottky diode frequency multipliers provide sufficient LO power to allow continuous frequency tuning from 1.009 to 1.046 THz and from 1.261 to 1.275 THz. The mixer block is mounted in a side-looking liquid helium cryostat with a 0.47-mm-thick high-density polyethylene vacuum window. Incoming infrared radiation is attenuated by cooled Zitex filters mounted on the 77-K liquid nitrogen shield and He cold plate. Incoming radiation is coupled to the mixer via an off-axis 90 parabolic mirror, which is part of a frequency-independent optical train that images the feed aperture onto the telescope entrance pupil [14]. Mixer bias is supplied through a bias tee on the third port of a 2–4-GHz circulator, which precedes a low-noise cryogenic high electron-mobility transistor (HEMT) amplifier. After additional room-temperature amplification, IF output from the mixer passes through a 1.2-GHz-wide bandpass filter, centered at 3 GHz, to a calibrated power meter and a digital autocorrelation spectrometer with 3-MHz resolution. IV. RECEIVER PERFORMANCE A. Receiver Sensitivity The DSB receiver noise temperature is measured using the standard -factor technique in which room-temperature and liquid nitrogen cooled loads are alternately placed at the signal input (Fig. 1, position 4). The optimum bias point for low- noise receiver operation is determined by measuring the receiver noise temperature as a function of LO drive and mixer bias voltage. In Fig. 2, we display the – curves for our mixer with and without LO power applied at 1.037 THz. The receiver output in response to hot and cold loads is also shown. At the observatory site, we obtain optimal sensitivity, a receiver noise temperature of 1000 K, at bias points in the range of 0.7–0.8 mV and 21–22 A. Note that the optimally pumped – curve is smooth and monotonic, and that the IF output power as a function of bias voltage has a smooth and rounded peak. For this

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Fig. 3. Spectrum of OCS gas measured in the laboratory. The line is pressure broadened so that it occupies more than one channel in the spectrum. Fig. 2. I –V curves of the HEB mixer at the operating region with and without LO drive at 1.0369 THz performed at the telescope. Also shown is the IF output power, monitored by a power meter, in response to hot (277 K) and cold (72 K) loads placed at the receiver input. The optimal region is shown by the open circle, and the measured Y factor is 1.18.

reason, the variation in noise temperature within the optimal region, marked by an open circle in Fig. 2, is small, approximately 2%, and the conversion efficiency is approximately constant at 16 dB. Finally, direct detection effects, which can result in erroneous noise calibration, are considered negligible in our waveguide mixer configuration; we observe only a 0.2% change in mixer current as the input switches between hot and cold loads. In the laboratory, we have also made receiver noise measurements up to 1.27 THz, where we obtain a receiver noise temperature of 1600 K. We have also measured the receiver noise temperature and relative conversion gain across the IF passband. From our data, we find a drop in conversion efficiency across the IF band, from 2.6 to 3.6 GHz, of approximately 2 dB, and estimate a 3-dB IF gain rolloff frequency of 2.2 GHz. With the MPI tuned to a center IF frequency 3.0 GHz, the receiver noise temperature increases by approximately 20% across the IF band. At the observatory site, we de-tune the MPI to a center frequency of 3.25 GHz, which results in a more uniform sensitivity across the IF band. We have found that the receiver sensitivity at the telescope is generally better (by a few percent) than that measured in the laboratory. This is most likely the result of a decreased helium bath temperature due to the reduced atmospheric pressure (530 mbar) at altitude, and a reduction in losses in the signal path due to a reduction in water vapor content of the atmosphere at the dry high altitude site. B. Gas Cell Measurement In order to verify the heterodyne performance of the entire receiver system, we made a gas-cell measurement in the laboratory. We used carbonyl sulfide (OCS) gas as a spectral line source at 1.030655 THz, and controlled the emission linewidth by changing the gas pressure in the cell. The gas cell, a 0.6-m-long stainless-steel cylinder with polyethylene windows at each end, was positioned in the signal beam of the receiver. The OCS line was observed by making a series

of ON and OFF integration pairs using the correlator as a spectrometer. The “ON” integrations were made with a room temperature load behind the cell and the “OFF” integrations were made with a liquid nitrogen cooled load behind it. Since the gas was at room temperature, no emission or absorption appeared in the ON spectra, while an emission line appeared in the OFF spectra. When such a pair is combined as (ON–OFF)/OFF, the spectral line shows up in absorption. The receiver was able to detect the OCS line on each integration pair, and high signal to noise was obtainable through the summation of several ON–OFF pairs. A spectrum formed from 64 5-s ON–OFF pairs is shown in Fig. 3. In these measurements, the receiver noise temperature, measured at the input to the gas cell, was approximately 2000 K, compared to 1000 K measured directly in front of the receiver. The increased noise is largely due to truncation of the signal beam by the gas cell and losses in the gas cell windows and humid summer air. C. Beam Measurement We measured the near field beam pattern of the receiver at 1.028 THz to confirm alignment of the receiver coupling optics, which had been previously aligned at visible wavelengths. We were able to produce repeatable maps of the electric field amplitude and phase with high signal to noise, and made a series of transverse cuts at planes along the signal input path. In Fig. 4, we show a two-dimensional amplitude map of the receiver beam, which is very well fit by the lowest order Gaussian mode (with 97% or greater coupling) and confirms excellent radio alignment. The vector beam measurement procedure and results are discussed in greater detail in [15]. D. Astronomical Measurements The receiver system is currently installed at the RLT on Cerro Sairecabur in Northern Chile. This Cassegrain telescope has an 80-cm diameter primary and is located at an altitude of 5525 m (18 100 ft), at a site where the atmosphere is unusually transmissive at frequencies above 1 THz [16]. The RLT began operations in November 2002. During the initial commissioning phase, we successfully conducted astronomical observations in both the 850-GHz and 1.03-THz atmospheric windows. In Fig. 5, we show two fully resolved


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V. CONCLUSION We have developed a heterodyne low-noise HEB receiver suited for observation in atmospheric windows between 800–1300 GHz. The DSB receiver noise temperature obtained at the telescope is around 1000 K at 1.0369 THz. At press time, this receiver is still providing useful astronomical data at supra-terahertz frequencies. Observations have now been made at frequencies up to 1.267 THz using this and other HEBs in the same receiver system. ACKNOWLEDGMENT The authors sincerely thank N. Kaurova and K. Smirnov for fabricating the HEB mixer elements at the Moscow State Pedagogical University, Moscow, Russia, R. Plante, Smithsonian Astrophysical Observatory, Cambridge, MA, for assistance in the construction of the telescope, and M. Diaz, Boston University, Boston, MA, and S. Radford, National Radio Astronomy Observatory, Tucson, AZ, for help with RLT observations.

Fig. 4. Amplitude beam pattern of the receiver as measured at 1.028 THz. The contours are labeled in decibels relative to the peak signal. The beam appears nearly circular down to at least 25 dB.

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Fig. 5. Two spectra of the OMC region obtained with the RLT. The solid line is the spectrum at the center of the source, where gas outflow causes a significant kinetic broadening of the spectral line. The dashed line is the spectrum at a point 50 arcseconds north and 150 arcseconds west. At this location, very little outflow is evident.

spectra of the rotational transition of CO (1.0369 THz) taken at different positions within the Orion Molecular Cloud. The kinetically broadened spectrum, taken at the center of OMC1, is a result of gas motion at the center of the outflow. The narrow spectrum is taken several arc minutes from the center of the outflow where velocity gradients within the cloud are small. A complete discussion of the first astronomical results obtained with this receiver may be found in [17].

REFERENCES [1] T. G. Phillips and J. Keene, “Submillimeter astronomy,” Proc. IEEE, vol. 80, pp. 1662–1678, Nov. 1992. [2] S. Paine et al., “A Fourier transform spectrometer for measurement of atmospheric transmission at submillimeter wavelengths,” Pub. Astronom. Soc. Pacific, vol. 112, pp. 108–118, Jan. 2000. [3] S. Matsushita et al., “FTS measurements of submillimeter opacity and other site testing at Pampa la Bola,” Proc. SPIE, vol. 4015, pp. 378–389, July 2000. [4] J. E. Carlstrom and J. Zmuidzinas, “Millimeter and submillimeter techniques,” in Reviews of Radio Science 1993–1995, W. R. Stone, Ed. Oxford, U. K.: Oxford Univ. Press, 1996. [5] A. Karpov, D. Miller, F. Rice, J. Zmuidzinas, J. A. Stern, B. Bumble, and H. G. LeDuc, “Low noise 1.2 THz SIS mixer,” in Proc. 12th Int. Space Terahertz Technology Symp., San Diego, CA, 2001, pp. 21–22. [6] D. E. Prober, “Superconducting terahertz mixer using a transition-edge microbolometer,” Appl. Phys. Lett., vol. 62, pp. 2119–2121, 1993. [7] E. M. Gershenzon, G. N. Goltsman, I. G. Gogidze, A. I. Elantiev, B. S. Karasik, and A. D. Semenov, “Millimeter and submillimeter range mixer based on electronic heating of superconducting films in the resistive state,” Superconductors, vol. 3, pp. 1582–1597, 1990. [8] S. Cherednichenko et al., “1.6 THz receiver for the far infrared space telescope,” Physica C, vol. 372–376, no. 1, pp. 427–431, 2002. , “A broadband terahertz heterodyne receiver with an NbN HEB [9] mixer,” in Proc. 13th Int. Space Terahertz Technology Symp., Cambridge, MA, 2002, pp. 85–94. [10] D. V. Meledin et al., “Study of the IF bandwidth of NbN HEB mixers based on crystalline quartz substrate with an MgO buffer layer,” IEEE Trans. Appl. Superconduct., vol. 13, pp. 164–167, June 2003. , “The sensitivity and IF bandwidth of waveguide NbN hot electron [11] bolometer mixers on MgO buffer layers over crystalline quartz,” in Proc. 13th Int. Space Terahertz Technology Symp., Cambridge, MA, 2002, pp. 65–72. [12] J. Kawamura et al., “Terahertz-frequency waveguide NbN hot electron bolometer mixer,” IEEE Trans. Appl. Superconduct., vol. 11, pp. 952–954, Mar. 2001. [13] S. Cherednichenko, P. Yagoubov, K. Il’in, G. Goltsman, and E. Gershenzon, “Large bandwidth of NbN phonon cooled hot-electron bolometer on sapphire substrate,” in Proc. 8th Int. Space Terahertz Technology Symp., Cambridge, MA, 1997, pp. 245–257. [14] T.-S. Chu, “An imaging beam waveguide feed,” IEEE Trans. Antennas Propagat., vol. AP-31, pp. 614–619, July 1983. [15] C.-Y. E. Tong, D. V. Meledin, D. P. Marrone, S. N. Paine, H. Gibson, and R. Blundell, “Near field vector beam measurements at 1 THz,” IEEE Microwave Wireless Comp. Lett., vol. 13, pp. 235–237, June 2003. [16] R. Blundell et al., “Prospects for terahertz radio astronomy from Northern Chile,” in Proc. 13th Int. Space Terahertz Technology Symp., Cambridge, MA, 2002, pp. 159–166.

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[17] D. P. Marrone et al., “A map of OMC-1 in CO J = 9 8,” Astrophys. J., vol. 612, Sept. 2004. [Online]. Available: http://xxx.lanl.gov/abs/astro-ph/0405530, to be published.

Denis V. Meledin was born in Arkhangelsk, Russia, in 1974. He received the Ph.D. degree in radiophysics from the Moscow State Pedagogical University, Moscow, Russia, in 2003. From 2000 to 2003, he was a Pre-Doctoral Fellow with the Submillimeter Receiver Laboratory, Smithsonian Astrophysical Observatory. He is currently a Post-Doctoral Fellow with the Advanced Receiver Development Group, Onsala Space Observatory, Onsala, Sweden, where he is involved with radio instrumentation. His current research interests include superconducting low-noise heterodyne receivers for terahertz astronomical applications and the design of microwave and submillimeter-wave components.

Daniel P. Marrone received the B.S. degrees in physics and astrophysics from the University of Minnesota, Twin Cities, in 2001, the A.M. degree in astronomy from Harvard University, Cambridge, MA, in 2003, and is currently working toward the Ph.D. degree in astronomy at Harvard University. Since 2001, he has been with the Submillimeter Receiver Laboratory, Harvard–Smithsonian Center for Astrophysics, Cambridge, MA. His projects include the Receiver Laboratory Telescope, which is the first ground-based telescope dedicated to terahertz observations, and terahertz receiver development. He is also involved with polarization hardware and submillimeter interferometric polarimetry with the Submillimeter Array, Mauna Kea, HI.

C.-Y. Edward Tong (M’89) was born in Hong Kong. He received the B.Sc. (Eng.) degree from the University of Hong Kong, Hong Kong, in 1983, the ˆ e d’Ingénieur degree from the Engineering School, ENSERG, Grenoble, Diplom France, in 1985, and the Ph.D. degree from the Université de Joseph Fourier, Grenoble, France, in 1988. From 1985 to 1988, he was with the Institut de Radio Astronomie Milimétrique, Grenoble, France, where he studied low-noise superconducting receivers for millimeter wavelengths. From 1989 to 1991, he was a Post-Doctoral Fellow with the Communications Research Laboratory, Tokyo, Japan. since 1991, he has been with the Harvard–Smithsonian Center for Astrophysics, Cambridge, MA, where he is a staff member responsible for the development of ultra-sensitive superconducting receivers for submillimeter waves. He is also an Astronomy Lecturer with Harvard University, Cambridge, MA. His research interests include superconducting devices and their applications to high frequencies, low-noise heterodyne instrumentation, submillimeter and quasi-optical techniques in microwave and antenna measurement, and the time-domain solution of three-dimensional electromagnetic problems.

Hugh Gibson, photograph and biography not available at time of publication.

Raymond Blundell was born in Liverpool, U.K. He received the B.Sc. and Ph.D. degrees in electrical and electronic engineering from The University of Leeds, Leeds, U.K. In 1977, he joined the Thorn–EMI Group, where he was engaged in the development of scale-model radar systems. From 1980 to 1989, he was with the Institut of Radio Astronomic Millimétrique, Grenoble, France, where he led a small group responsible for the development of low-noise millimeter heterodyne receivers. In 1989, he became Director of the Submillimeter Receiver Laboratory, Harvard–Smithsonian Center for Astrophysics, Cambridge, MA, as well as being a Lecturer in astrophysics with the Department of Astronomy, Harvard University, Cambridge, MA. His research interests include millimeter and submillimeter techniques, superconducting tunnel-junction mixers, solid-state oscillators and frequency multipliers, low-noise amplifiers, quasi-optical components, and 4-K refrigeration systems.

Scott N. Paine (M’92) received the B.S. degree in applied physics from the California Institute of Technology, Pasadena, in 1984, and the Ph.D. degree in atomic physics from the Massachusetts Institute of Technology (MIT), Cambridge, in 1992. Since August 1992, he has been with the Submillimeter Receiver Laboratory, Harvard–Smithsonian Center for Astrophysics, Cambridge, MA. His research interests include millimeter- and submillimeter-wave optics and instrumentation, and atmospheric measurements and modeling.

D. Cosmo Papa joined the Massachusetts Institute of Technology (MIT), Cambridge, in 1942, where he was involved with microwaves and mechanical engineering with the Radiation Laboratory and then with the Research Laboratory of Electronics. In 1961, he joined the Radio Astronomy Group, and continued with them until 1988. In 1989, he joined the Submillimeter Receiver Laboratory, Harvard–Smithsonian Center of Astrophysics, Cambridge, MA, where he is involved in the development of receivers in the submillimeter-wavelength range.

Michael Smith is currently working toward the Bachelors degree in mechanical engineering at Northeastern University, Boston, MA. In 1980, he joined M/ACom, where he was involved in the research and development of missile and radar systems in the Radar Products Division, Defense Department Subcontractor. In 1990, he joined the firm’s engineering facilities, where he was involved in the development of millimeter-wavelength applications. He is currently with the Submillimeter Receiver Laboratory, Harvard–Smithsonian Center for Astrophysics, Cambridge, MA. He is currently involved in the research, development, and deployment of hardware for the Submillimeter Array, Mauna Kea, HI, and terahertz frequency receivers for future ground-based initiatives.

Todd R. Hunter received the B.S. degree in astronomy from Pennsylvania State University, University Park, in 1991, and the Ph.D. degree in astronomy from the California Institute of Technology, Pasadena, in 1996. His doctoral research concerned the design and construction of the first facility bolometer array camera for the California Institute of Technology (Caltech) Submillimeter Observatory on Mauna Kea. Since October 1996, he has been with the Submillimeter Receiver Laboratory, Harvard–Smithsonian Center for Astrophysics, Cambridge, MA. His current interests include high-frequency LO and receiver control, submillimeter interferometry, and the multiwavelength study of massive protostars.


James Battat received the Bachelors degree in physics from Brown University, Providence, RI, in 2001, the Masters degree in astronomy from Harvard University, Cambridge, MA, in 2003, and is currently working toward the Ph.D. degree in astronomy at Harvard University. He has authored data reduction software for the Wilkinson Microwave Anisotropy Probe satellite as an undergraduate student. As a graduate student, he has developed a radiometric system to monitor atmospheric phase fluctuations with the Submillimeter Array interferometer, Mauna Kea, HI. This system, a submillimeter wave analog to adaptive optics, improves the angular resolution and coherence of interferometric observations.

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Boris Voronov received the Masters degree in semiconductor materials and devices from the Moscow Steel and Alloys Institute, Moscow, Russia, in 1969. He is the Head of the Processing Laboratory, Moscow State Pedagogical University, Moscow, Russia. He has authored or coauthored approximately 60 publications in scientific journals. His professional interest includes solid-state physics, vacuum science, and technology, particularly ultra-thin superconducting film deposition.

Gregory Gol’tsman received the Ph.D. degree in radiophysics and the Doctor of Science degree in semiconductor and dielectric physics from the Moscow State Pedagogical University, Moscow, Russia, in 1973 and 1985, respectively. He is currently the Chairperson of the general and experimental Physics Department, Moscow State Pedagogical University. He has authored or coauthored over 160 publications in scientific journals and has given over 170 presentations at scientific conferences. His scientific interests are superconductivity, nonequilibrium phenomena in superconductors, semiconductors, and far-infrared spectroscopy, as well as terahertz and infrared detectors (including single-photon detectors) and terahertz mixers.