Advanced regime of the noncollinear two-phonon acousto-optical interaction governed by elastic waves of finite amplitude and optical spectrum analysis

Abstract

Principally new features of square-law nonlinearity specific to the noncollinear two-phonon acousto-optical interaction (AOI) governed by elastic waves of finite amplitude in birefringent crystals are revealed and studied. An additional degree of freedom represented by the dispersive birefringence factor, which can be distinguished within this nonlinear phenomenon, is found and characterized. This physical degree of freedom gives us a one-of-a-kind opportunity to apply the two-phonon AOI in practice for the first time. The needed theoretical analysis is developed, and proof-of-principle experiments performed with a specially designed unique wide-aperture acousto-optical cell (AOC) made of the calomel (α-Hg2Cl2) single crystal, are presented. The results of experiments with this AOC confirm the elaborated theory with numerical estimations and support the proposed application to optical spectrum analysis with the doubled resolution.