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An optimized leaf-spring apparatus for applying uniaxial stress to a Ge:Ga far-infrared photoconductor has been designed and tested. This design has significant advantages for space applications which require high quantum efficiency and stable operation over long periods of time. The important features include adequate spring deflection with relatively small overall size, torque-free stress, easy measurement of applied stress, and a detector configuration with high responsivity. One-dimensional arrays of stressed photoconductors can be constructed using this design. A peak responsivity of 38 A/W is achieved in a detector with a cutoff wavelength of 200 microm, which was operated at a temperature of 2.0 K and a bias voltage equal to one half of the breakdown voltage.

A detailed analysis is presented of the Michelson polarizing interferometer suggested by Martin and Puplett. This instrument has many favorable properties for use as a far ir Fourier spectrometer. The effect of misalignments and imperfections of the optical components on the instrumental performance is calculated. Based on these results, we give a method of aligning the interferometer which optimizes its performance. In addition, this instrument may be used to measure the optical transfer function of a component in the output beam as a function of both spatial and optical frequency. A procedure is described by which this may be done.

We have fabricated low pass filters made of spherical glass beads embedded in polyethylene and measured the transmittance at room temperature and 1.3 K as a function of the diameter and the filling factor of the glass beads. The cutoff frequency is a function of the bead diameter. Compared with the transmittance of thin glass plates or Fluorogold filters, these filters have a sharper cutoff due to the effect of scattering by the spherical beads. This effect becomes prominent at low temperature, because of the decrease in the absorption coefficient of glass itself. The glass bead filters have very low transmittance above the cutoff frequency. One of the filters we fabricated has a transmittance of <5 x 10(-4) between 50 and 1000 cm(-1).

We report the performance of a rocket-borne absolute radiometer which was designed to measure the diffuse brightness of the sky in six passbands between 100 microm and 1 mm. The radiometer consisted of a horn antenna and a photometer, both of which were cooled to 1.2 K by liquid (4)He. The performance of the instrument was satisfactory, but no astrophysical data were obtained during the flight because a lid covering the horn antenna failed to pen. Another flight of a similar apparatus is planned for 1986.

A horn antenna with low sidelobe response has been fabricated for a rocket-borne observation of the diffuse brightness of the sky at submillimeter wavelengths. The antenna consists of a Winston concentrator which defines the field of view and a flared baffle which minimizes diffraction. The sidelobe response for lambda = 337 microm was measured to be <10(-9) at an angle of 70 degrees from the optical axis. Calculations are reported which illustrate the contributions of diffraction and scattering to the sidelobe response.