Nonlinear Recording In Dichromated Gelatin

Gratings formed in dichromated gelatin due to the nonlinear recording characteristics of the material are investigated for a range of single and double exposures. We found that for a high enough single exposure not only the grating with the grating vector K but spatial harmonics at 2K and 3K are also present. Similarly, for double exposures (sequential exposures for gratings with grating vectors K1 and K2) additional harmonics with wave vectors K1 - K2, K1 + K2, 2K1 and 2K2 may be detected. We developed a simple theory to relate the modulation strength of each grating to a nonlinear recording characteristics of dichromated gelatin, and compare the theoretical values to those derived from experiments. Data is presented as plots of modulation against exposure. For most cases such procedure gives good agreement between theoretical and experimental results but it needs to be noted that for the transmission dip corresponding to the K1 - K2 case there may be significant contribution due to multiple diffraction at gratings with grating vectors K1 and K2. The application of this theory to a coupled wave solution of two sequentially recorded transmission gratings is discussed. We also apply the theory to the problem of varying the beam ratio of single reflection and transmission gratings. Experimental results are presented.