Method of bragg angle adjustments for copying holograms
 A method of copying a thick hologram, recorded at wavelength .lambda..sub.1, so that the copy can be efficiently read out with a beam .lambda..sub.3 at the same incident angle as used to efficiently read out the original. The method involves copying the hologram using wavelength .lambda..sub.2 at a predetermined incident angle, which incident angle provides fringe angles in the copy to yield maximum diffraction efficiency of the read-out beam .lambda..sub.3. 
The United States of America as represented by the Secretary of the Army
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Charles R. Carl D. Joseph G. M.
Christensen Leonard Duthie