Spectrometer, Grating, Convex
Wednesday, September 20, 2006
A Convex Grating Spectrometer has been designed and developed with a 1:1 magnification Offner relay mirror system, which is modified by replacing the single concave spherical primary mirror with two concave spherical mirrors. The two mirrors of the same or different radii are positioned at particular distances from a concentric convex spherical diffraction grating (which has replaced the convex secondary mirror of the Offner optical system). The spherical diffraction grating has its grooves parallel to the entrance slit of the spectrometer configuration.
By adjusting the mirror distance locations and the mirror reflection angular orientation, all aberrations are corrected without the need to increase the size of the spectrometer for a given entrance slit size used to correct astigmatism. This situation allows the imaging spectrometer volume to be less for any given application than would be possible with a conventional imaging spectrometer while providing excellent spatial and spectral imaging of the slit image spectra over the focal plane.
The light beam from the image field passes through an entrance slit and is diffracted by the diffraction grating with the grooves (lines) parallel to the slit. The image on the focal plane can be displayed or recorded using the output signal from a variety of photodetectors.
The Spectrometer consisted of a large spherical mirror facing a concentric convex diffraction grating. The center of curvature of both the mirror and the grating are at the same point on a plane that contains the object (slit) on one side of the convex diffraction grating and an image detector array on the other side of the convex diffraction grating (opposite the slit). The diffraction grating has its groove lines parallel to the slit.
Tilt of the diffraction grating does affect the symmetry of the optical system and does introduce coma into the image. The all reflection configuration can perform in the spectral range from the ultraviolet to the far infrared. The flatness of the focal plane image allows for the use of pixel array photodetectors.
Source: “Design of grating spectrometer from a 1:1 Offner mirror system” by Deborah Kwo, George Lawrence and Michael P. Chrisp; SPIE Procedures, Vol.818, 1987, pages 275-279
Reference:
1) United States Patent Number 5,880,834, inventor Michael P. Chrisp
Patent Counsel, NASA, JPL, Resident Office; Reference Number NPO-19293
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posted by JD52 @ 8:33 PM,
