Contains reports on five research projects.Joint Services Electronics Program (Contract DAAB07-76-C-1400)National Aeronautics and Space Administration (Grant NGR 22-009-526)National Aeronautics and Space Administration (Grant NSG-7328)National Aeronautics and Space Administration (Contract NAS5-24096

Benford, Richard L.

Downey, Patricia M.

Frerking, Margaret A.

Halpern, Mark

Muehlner, Dirk J.

Shoemaker, David H.

Wiess, Rainer

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X. INFRARED INSTRUMENTATION AND ASTRONOMYAcademic and Research StaffProf. Dirk J. MuehlnerProf. Rainer WeissRichard L. BenfordGraduate StudentsPatricia Downey Mark HalpernMargaret A. Frerking David H. Shoemaker1. INFRARED HETERODYNE DETECTIONJoint Services Electronics Program (Contract DAAB07-76-C-1400)Dirk J. Muehlner, Richard L. Benford, Margaret A. FrerkingA continuously tunable infrared heterodyne receiver was developed with the originalintention of using it for very high spectral resolution astronomical observations. Thecomplete detector, including a PbSnSe diode laser local oscillator, a HgCdTe photodiodemixer and associated optical components, was assembled in a small dewar. The dewarand additional transfer opticals made a compact package which could be mounted as aunit on even a small astronomical telescope.The technology of tunable diode lasers for the mid infrared is new and we encoun-tered considerable difficulties due to deterioration of the early lasers when they werecycled between room and liquid helium temperatures. Late in 1976 we obtained (fromLaser Analytics, Inc.) a diode laser which operated at liquid nitrogen temperature,making it practical to store the instrument cold. This longest-lasting of our diodelasers was used in late 1976 to make heterodyne measurements of absorption of solar-iradiation by ozone in the earth' s atmosphere near 1010 cm- . Preliminary results onthis project were described in RLE Progress Report No. 119 (p. 31). The work waspublished I in essentially the same form, except that a better match of a calculatedspectrum to the observed one was obtained by using the latest available line param-eters 2 for ozone. The most complete description of the work, including results of highresolution laboratory absorption spectra of ozone, appears in the Ph. D. thesis3 ofMargaret Frerking.No further experimental work was done after the ozone measurements were com-pleted, and the project came to an end, after having demonstrated the potential of thecompact heterodyne receiver, with the completion of Ms. Frerking' s thesis.References1. Applied Optics 16, 526 (1977).PR No. 120 43'(X. INFRARED INSTRUMENTATION AND ASTRONOMY)2. A. Barbe, C. Secroun, P. Jouve, N. Monnanteuil, J. C. Depannemaeker, B. Duterage,J. Bellet, and P. Pinson, J. Mol. Spectrosc. 64, 343-364 (1977).3. Margaret A. Frerking, "Heterodyne Detection of Infrared Molecular Lines," Ph. D.Thesis, Department of Physics, M. I. T., August 1977.2. MEASUREMENTS OF THE LARGE-SCALE ANGULAR DISTRIBUTIONOF THE COSMIC BACKGROUND RADIATION AT MILLIMIETERAND SUBMILLIMETER WAVELENGTHSNational Aeronautics and Space Administration (Grant NGR 22-009-526)Rainer Weiss, Dirk J. Muehlner, Richard L. BenfordFor several years we have been making balloon flights with a dual-channel differen-tial radiometer to measure the anisotropy in the angular distribution of the 30K cosmicbackground radiation on angular scales of 17'. The radiometer has passbands of3-10 cm-1 and 10-25 cm-1 . We have established that the radiation is isotropic to a fewparts in a thousand over one half of the sky. At this level of sensitivity we are observinganisotropies caused by interstellar dust clouds which exhibit a steeply increasing spec-trum with frequency. The galactic plane is a major source of nonuniform width, tem-perature, and emissivity. Other sources have been discovered, in particular, a diffuseand extended region in the northern sky in the vicinity of W1. The analysis of the cos-mic component has been complicated by these sources. Further progress requires theaddition of more spectral channels in the radiometer in order to characterize the sourcesand allow their removal in the background measurement.Even though isotropy measurements at smaller frequencies are less troubled bythese sources and may have succeeded in measuring the anisotropy caused by the motionof the Earth against the primeval plasma, isotropy measurements must be carried outat several wavelengths so that spectra of the anisotropy can reveal the true sourceof the anisotropy.This program is active and is now being administered by the Department of Physics.3. SKY SURVEY AT MILLIMETER AND SUBMILLIMETERWAVELENGTHSNational Aeronautics and Space Administration (Grant NGR 22-009-526)Rainer Weiss, Dirk J. Muehlner, Richard L. BenfordIn an effort to understand the results of the isotropy experiments, we have been car--1 and 10-25 cm- bands with anrying out a sky survey from balloons in the 3-10 cm   PR No. 120(X. INFRARED INSTRUMENTATION AND ASTRONOMY)angular resolution of 1.50. Two flights have been made which have mapped the galacticplane -2 < 1 < 1200. The maps reveal that the galactic plane is a strong source in the-1 II10-25 cm band, the galactic center is about 1/300 as bright as the moon in the samebeam size. The galactic plane is not uniform in width but varies from a size as smallas the beam size to over 80. The spectral index varies more steeply than the frequencyto the third power.More survey flights will be made in the next year using new bolometers and two morespectral channels.This program has been transferred to the Department of Physics.4. INTEGRATED SILICON BOLOMETERNational Aeronautics and Space Administration (Grant NSG-7328)Rainer Weiss, Patricia DowneyBroadband composite bolometers constructed entirely of silicon have been tested.The technique of manufacture is the following. A resistance thermometer is ion-implanted in a high-purity single-crystal wafer of silicon. The wafer, after masking,is etched leaving a central square 5 millimeters on a side supported by a silicon spiderthat makes thermal contact to a large silicon frame thermally connected to the heat bath.The central square is coated with a thin film of conductor that is the radiation absorbingsurface.At present, the best detector has had a 5-ms time constant and a radiation NEP of3 X 10 - 1 4 W/Hz / 2 at 1.5 0 K. The observed performance is within a factor 1.2 of thecalculated performance of the specific device. We expect with further refinement ofpresent techniques to construct detectors with a NEP of a few 10 - 15 W/Hzl/2 and timeconstants in the 10' s of milliseconds.Difficulties have been encountered in maintaining reasonable yields due to nonunifor-mity in the ion implants. Until this problem is solved, the initial concept of manufac-turing detector arrays is unpromising. Future work will be directed toward constructingbolometers operable at 0.3 0 K using He 3 cryogen. Detectors of this style do not exhibitKapitza resistance and should have NEP' s that vary as T - 5/2This project has been transferred to the Department of Physics.PR No. 120(X. INFRARED INSTRUMENTATION AND ASTRONOMY)5. COSMIC BACKGROUND EXPLORER SATELLITE (COBE)National Aeronautics and Space Administration (Contract NAS5-24096)Rainer Weiss, Mark Halpern, David H. ShoemakerWe are participating in the phase B study of a satellite mission to be flown in 1983to measure the spectrum and the large-scale angular distribution of the cosmic back-ground radiation in four bands, as well as the diffuse infrared background between 2 and300 micron wavelengths. Rainer Weiss is team leader of the study and coinvestigator onthe instrument to measure the spectrum of the radiation. The phase B study will culmi-nate in the definition, costing, and specifications of the Fourier transform spectrometerdesigned to measure the spectrum of the cosmic background radiation with a signal-to-noise exceeding 1000/1 at the blackbody peak in angular resolution elements between-13' and 50. The spectral resolution of the instrument will be better than .5 cm- at fre-quencies less than 20 cni1. The spectral range of the instrument extends to 100 cm-1The coordinated observations of the mission should provide the most definitive mea-surements of the properties of the background radiation limited only by the "noise" dueto the local astrophysical environment.This project has been transferred to the Department of Physics.PR No. 120

Infrared Instrumentation and Astronomy

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Infrared Instrumentation and Astronomy

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