in the infrared region of an incident optical wave to that end it proposes the use of a birefringent acousto optic crystal whereof the propagation speed of acoustic waves is slow such as compounds of mercury which acousto optic crystal comprises on one of its faces a piezoelectric transducer designed to generate a transverse acoustic wave with wave vector whereof the energy propagates according to the same axis but in the opposite direction to the energy of the incident optical wave knowing that the optical wave resulting from the acousto optic interaction between the incident optical wave and the acoustic wave with wave vector is diffracted perpendicularly or almost perpendicularly to the direction of the incident optical wave application_number US 23735408 A description in the example depicted in fig1 the schematic depiction of the optical slowness curves upper dials and the acoustic slowness curve lower dials shows in the orthonormal system defined by the axes 110 and 001 of the birefringent crystal that two solutions are possible which lead to acoustic wave vectors k 2 u03c0 u0192 v u03b8 a of very different lengths and therefore very different acoustic frequencies u0192 in the visible and near infrared region where the acousto optic material of choice is teo 2 only the short vector k can be used since the long vector corresponds to.