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AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration
InventorMichael P. Chrisp
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A 1:1 Offner mirror system for imaging off-axis objects is modified by replacing a concave spherical primary mirror that is concentric with a convex secondary mirror with two concave spherical mirrors M1 and M2 of the same or different radii positioned with their respective distances d1 and d2 from a concentric convex spherical diffraction grating having its grooves parallel to the entrance slit of the spectrometer which replaces the convex secondary mirror. By adjusting their distances d1 and d2 and their respective angles of reflection .alpha. and .beta., defined as the respective angles between their incident and reflected rays, all aberrations are corrected without the need to increase the spectrometer size for a given entrance slit size to reduce astigmatism, thus allowing the imaging spectrometer volume to be less for a given application than would be possible with conventional imaging spectrometers and still give excellent spatial and spectral imaging of the slit image spectra over the focal plane.
A convex spherical diffraction grating imaging spectrometer comprising
A convex spherical diffraction grating imaging spectrometer based on a 1:1 Offner mirror system for imaging spectra of off-axis images through an entrance slit, comprising concave spherical mirrors (M1) and (M2) positioned at respective distances (d1) and (d2) from a concentric convex spherical diffraction grating having grating grooves parallel to an entrance slit with respective angles of reflection (.alpha.) and (.beta.), said angles of reflection being defined as the angles between their respective incident and reflected rays, thereby to provide optimum correction of all aberrations including astigmatism with excellent spatial and spectral resolution of said entrance slit image spectra on a focal plane parallel to a plane from which radiation is received through said entrance slit, wherein said distance (d1) and angle of reflection (.alpha.) of said concave spherical mirror (M1) from said concentric convex spherical diffraction grating are greater than said distance (d2) and angle of reflection (.beta.) of said concave spherical mirror (M2) from said concentric convex spherical diffraction grating.
A convex spherical diffraction grating imaging spectrometer based on a 1:1 Offner mirror system for imaging spectra of off-axis images through an entrance slit, comprising concave spherical mirrors (M1) and (M2) positioned at respective distances (d1) and (d2) from a concentric convex spherical diffraction grating having grating grooves parallel to an entrance slit with respective angles of reflection (.alpha.) and (.beta.), said angles of reflection being defined as the angles between their respective incident and reflected rays, thereby to provide optimum correction of all aberrations including astigmatism with excellent spatial and spectral resolution of said entrance slit image spectra on a focal plane parallel to a plane from which radiation is received through said entrance slit, wherein radii R1 and R2 of said concave spherical mirrors M1 and M2 are equal.
A convex spherical diffraction grating imaging spectrometer based on a 1:1 Offner mirror system for imaging spectra of off-axis images through an entrance slit, comprising concave spherical mirrors (M1) and (M2) positioned at respective distances (d1) and (d2) from a concentric convex spherical diffraction grating having grating grooves parallel to an entrance slit with respective angles of reflection (.alpha.) and (.beta.), said angles of reflection being defined as the angles between their respective incident and reflected rays, thereby to provide optimum correction of all aberrations including astigmatism with excellent spatial and spectral resolution of said entrance slit image spectra on a focal plane parallel to a plane from which radiation is received through said entrance slit, wherein radii (R1) and (R2) of said concave spherical mirrors (M1) and (M2) are selected to be different for optimum spatial and spectral resolution of said spectra imaged through said slit.
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