Analysis of propagation at the second-order Bragg angle of a thick holographic grating*

Algebraic expressions are derived for the diffraction efficiency of the first and second orders of a holographic grating recorded in a thick, pure-phase material with a nonlinear exposure response for readout at the second-order Bragg angle. The results demonstrate the importance of double diffraction by the fundamental grating as well as diffraction by the harmonic grating in producing the second order. It is shown that the strong cross coupling between two gratings constructed in the same emulsion with a common construction angle is a limiting case of the double diffraction that occurs in single gratings. Experimental results from gratings constructed in dichromated gelatin are presented to verify the theory.