Influence of acoustic energy walk-off on acousto-optic diffraction characteristics

• Modified Raman–Nath equations are derived for slanted acoustic beams.
• Characteristics of acousto-optic interactions are analyzed in cases isotropic and anisotropic diffraction.
• Broadening coefficients are introduced and calculated for characterization of acoustic walk-off influence.
• The necessity of taking into account of the acoustic walk-off is proved.

Influence of acoustic beam energy walk-off on characteristics of Bragg diffraction of light is studied theoretically and experimentally by the example of a paratellurite single crystal. Two cases of isotropic and anisotropic light scattering are examined. Angular and frequency characteristics of acousto-optic interaction are calculated in wide ranges of Bragg angles and ultrasound frequencies by means of modified Raman–Nath equations. It is shown that the walk-off can substantially change the width of angular and frequency ranges, resulting in their narrowing or broadening subject to position of the operating point in the Bragg angle frequency characteristic. Coefficients of broadening are introduced for characterization of this effect. It is established that frequency dependences of the broadening coefficients are similar to the Bragg angle frequency characteristics. Experimental verification of the calculations is carried out with a paratellurite cell of 10.5° crystal cut.