Large-size distortion-free computer-generated holograms in photoresist.

Holograms, derived from computer calculations (e. g., Ref. 1) have gained interest for a number of applications, like spatial filtering, and, in particular, for interferometric testing of aspheric surfaces in optics production due to their potential to create physically wavefronts from just a mathematical description. The most common way of making the hologram is to have the pattern, which has been calculated by the computer, drawn in a large scale by a plotter. The drawing is reduced photographically onto high-resolution film in one or two steps by a factor of 20-400. In the special application to generating wavefront standards for testing aspheric optical elements, computer-generated holograms are handicapped by several serious technical de­ ficiencies. Their low space-bandwidth product limits the diffraction angle and/or wavefront accuracy' and, hence, requires the use of additional optical elements for the testing of deep aspherics (e. g., Refs. 6, 10, 12, 14, 15, 17). Position nonlinearities of the plotting device, aberrations of the reducing lens, and minute scale errors in the demagnification process cause errors in the wavefront generated which are much larger than the accuracy of λ/10 or λ/20 usually re­ quired for wavefront standards. The space-bandwidth product of ordinary holograms generated in laser light by a signal wavefield and a coherent off-axis reference beam may easily be 10 and more along one coordinate if the carrier frequency is, say, 1000 cycles/mm and the plate is 10 cm wide. Data on display devices used for drawing computer-generated holograms indicate that plotters of different brands may provide between 900 × 900 and 6000 × 6000 or 7000 × 7000 discrete pen positions (e. g., Refs. 8, 18, 19), of which only about 1500 have been regarded as suffi­ ciently distortion-free. The paper size may be up to about 1 m. Plotting time for the largest type is about 10 h. Also the use of cathode-ray tube displays with, e. g., 1024 X 1024 points, a laser beam recorder with about 1400 × 1400 dis-

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