A high-quality, large numerical aperture Fresnel zone device is being developed to enhance the performance of a Fabry-Perot interferometer (FPI) system. As predicted by the theory, the contributions from the successive interference fringes transmitted by this multiple Fresnel aperture increase the throughput of the FPI system many fold. This versatile optical element can also function as a lens, an aperture, and a filter resulting in a very compact system. For a given FPI resolution, a dramatic increase in the throughput and significant reduction in the instrument size attained by this experimental approach offers broad possibilities for major scientific advances for faint radiation measurements in several areas including astronomy, remote sensing of the atmosphere, x-ray microscopy, plasma research, and neutron imaging.
An immersion grating with a high refractive index, n, increases the spectral resolution by a factor n over that of a reflective surface grating of equal length. A silicon immersion grating has been developed and tested; initial results are reported here.
A demonstration-prototype CO2-laser heterodyne spectrometer operating at 9-12 microns and suitable for long-term space missions is described and illustrated with extensive diagrams, drawings, photographs, and graphs of test performance data. The spectrometer has total volume 0.63 cu m, mass 30 kg, and power requirement 60-70 W, compatible with miniature-class Space Shuttle experiment payload specifications. It comprises three modules: (1) an optical front end with reflecting optics, a 2-GHz BW HgCdTe photomixer, and a 0-2-GHz 40-dB RF preamplifier; (2) a local oscillator with an RF-excited waveguide CO2 laser, a 75-percent-efficiency RF amplifier, a stepper-driven grating mode selector, and an etalon stabilized for over 30,000 h of use; and (3) an RF-filter-bank spectral-line receiver with a 25-MHz RF channel, 1.6-GHz IF spectral coverage, onboard instrument control, a serial link to the host computer, and highly integrated design.