Light diffraction by two parallel superposed ultrasonic waves of the frequency ratio 1:2.

The paper constitutes a concise study of light diffraction by two superposed ultrasonic waves of the frequency ratio 1:2, beyond the Raman-Nath diffraction regime. Relevant numerical simulations of light intensity distribution within separate diffraction orders are shown based on the Nth order approximation method (NOA). A comparison is given between generalized theoretical predictions (N=7) and simplified formulas of Mertens (N=2) [R. Mertens, Diffraction of light by two parallel superposed supersonic waves, one being the nth harmonic of the other: A critical study of the methods leading to approximate solutions in finite form, Proc. Indian Acad. Sci. 55 (1962) 63-98.]. Moreover, the results of the performed experiment are presented which indicate limited applicability range of Mertens' pioneer description of 1962.