TWO GENERALISED THEORIES DESCRIBING LIGHT DIFFRACTION BY ULTRASONIC PULSES :A. GENERATING-FUNCTION METHODB. LAPLACE-TRANSFORM METHOD

Abstract

As an extension from previous studies concerning the interaction of light with ultrasound of a purely sinusoidal form, two theoretical models describing light diffraction by ultrasonic pulses are derived starting from the Maxwell equations. Based on a generating function, the first model provides finite solutions for the amplitudes and intensities of the diffraction pattern and is restricted in validity to the Raman-Nath region. The second model consists of a numerical method developed by means of Laplacetransformations and covers as well the Raman-Nath as the Bragg region. Both new methods are compared with a theory based on the diffraction-integral theory, leading to the conclusion that the results of this latter method can be obtained from our models considering the extreme Raman-Nath regime ρ = 0. A general rule concerning the (a)symmetry properties of the diffraction spectrum at normal incidence has been derived from the extended Raman-Nath equations, using the generating function method.