Contains research objectives and summary of research.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DAAB07-71-C-0300National Aeronautics and Space Administration (Grant NGR 22-009-526)National Science Foundation (Grant GP-24254

Muehlner, J.

Owens, D. Kingston

Weiss, Rainer

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VII. GRAVITATION RESEARCHAcademic and Research StaffProf. R. WeissDr. D. J. MuehlnerR. L. BenfordGraduate StudentsD. K. OwensN. A. PierreM. RosenbluhRESEARCH OBJECTIVES AND SUMMARY OF RESEARCHThe research in this group is in the field broadly labeled experimental relativity,in particular, experiments related to the gravitational interaction and measurableconsequences of cosmological models.Specific Projects1. Astronomy in the Region 1-0. 1 mmOur present knowledge concerning the sky in the region between 1 mm and 0. 1 mmis still very limited. This region of the electromagnetic spectrum includes the iso-tropic blackbody background radiation which may be of cosmic origin, thermal radia-tion by intergalactic dust, and most likely discrete sources that are not visible in otherregions of the spectrum.Balloon-borne experiments performed during the past year have led to the following-iconclusions. (a) In the spectral region below 12 cm-1 the isotropic background spec-trum follows a Planck distribution appropriate to a blackbody at -2. 70 K. At this tem--lperature the spectral peak occurs at approximately 6 cm- . (b) In the region between12 cm-1 and 18 cm-1 we have measured an upper limit of radiation equivalent to a3. 30 K blackbody. We have measured a substantial atmospheric contribution in thisregion, but the actual value of this contribution is still unknown.We plan two specific projects during 1972. The first is to refine measurements-iof the spectrum of the isotropic background radiation in the region 12-20 cm . Bydesigning new filters, we hope to establish unambiguously the radiative contributionsof H20 and 0 3 in the upper atmosphere. We also hope to reach higher altitudes thanin previous flights.The second project is to make a measurement of the large-scale isotropy of thebackground radiation. This measurement is important in order to identify the sourceof this radiation. If the source is cosmic, then we may succeed in measuring theEarth's velocity relative to the frame of reference in which the universe is isotropic.J. Muehlner, R. WeissThis work was supported in part by the Joint Services Electronics Programs (U.S.Army, U.S. Navy, and U. S. Air Force) under Contract DAAB07 -71 -C-0300, and in partby the National Aeronautics and Space Administration (Grant NGR 22-009-526) and theNational Science Foundation (Grant GP-24254).QPR No. 104(VII. GRAVITATION RESEARCH)2. Far Infrared Detection(a) Development of nonmechanical modulators for the far infrared.(b) Far infrared detection by parametric up-conversion in CdS pumped by the5145 A line of the argon laser (see Quarterly Progress Report No. 100, p. 54).3. Gravitational Wave AntennaWe have made design studies and begun prototype construction of a long-baseline,broadband, electromagnetically coupled gravitational wave antenna. The antenna, inprinciple, should enable us to set a meaningful upper limit on the gravitational radia-tion from the Crab Nebula pulsar, as well as to measure the spectrum of the Webersources.D. K. Owens, R. Weiss4. Laser ResearchAn intracavity laser interferometer with circular polarization of novel design hasbeen constructed. With this instrument we have measured differences of the index ofrefraction for right- and left-circular polarization as little as 10 - 15 over a 1-cm opticalpath length. The instrument is useful in measuring small Verdet's constants, and wemay be able to measure intrinsic laser phase noise.D. K. OwensQPR No. 104 100

Gravitation Research

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Gravitation Research

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