Engineering topics
Publications and source records attributed to Rodgers, J. M..
Optical slit that reflects rather than transmits performs multiple functions for imaging infrared spectrometer. Serves as field reflector, field flattener, and entrance aperture for instrument. Reflecting slit narrow strip of spherical reflecting surface with intersecting spherical reflecting side surfaces that reject radiation originating outside slit region. Precision of slit geometry crucial in optical system.
Efficient linear dispersive element for spectrometer instruments achieved using several different glasses in multiple-element prism. Good results obtained in both two-and three-element prisms using variety of different glass materials.
In most real cases requiring simple null optics, the optical path difference cannot be reduced to zero but can be kept at a fractional wavelength level so that interferometric data reduction can be used to account for the residual error. In other cases, computer-generated holograms may be used to obtain apparently straight fringes when the desired surface is obtained. Two examples, one involving an f/2.5 concave oblate spheroid and the other a Paul-Baker secondary, are examined. It is shown that although the null tests are not generally perfect, the residual error is small and the tests are simple.
Space-based telescopes for sub-mm astronomy may require large, segmented primary mirrors. While spherical segments are the easiest to manufacture and test, a fast sphere produces large aberrations which must be corrected by one or more aspheric surfaces. Attention is presently given to an f/10 system with an f/0.7 spherical primary mirror and a field of view of + or - 1.5 min of arc. The third and fourth mirrors are conics, and the secondary is a 24th-degree power series on a base sphere. For sub-mm astronomy, a reasonable target for this design is a diffraction-limited image at 30 microns. In an effort to improve performance, the Wassermann-Wolf (1949) approach to aspheric design was applied.
A new wide-angle imaging spectrometer configuration is proposed where an all-reflecting Schmidt camera is used with a prism spectrometer to give a field of view up to 60 deg or more. Four different designs using this approach are presented. These are the Imaging Spectrometer Free Flyer, the Shuttle Imaging Spectrometer A, the Shuttle Imaging Spectrometer B, and the Wide-Field System. These systems are capable of broadband spectral coverage from 0.4 to 2.5 microns, with footprints 20 m on a side or less, and with swath widths hundreds of kilometers; they are capable of spectral resolving powers of 200 or more.