Deflection of a monochromatic THz beam by acousto-optic methods

Abstract

The possibility of controlled deflection of an electromagnetic THz beam of a free-electron laser by acousto-optic (AO) methods has been demonstrated for the first time. The material of the AO deflector was chosen to be single-crystal germanium, which has a fairly large refractive index and a relatively low absorption coefficient for electromagnetic waves. The absorption coefficient in germanium is at a wavelength . The diffracted beam intensity is shown to be maximum at an effective AO interaction length . A diffraction efficiency of 0.05 % at a travelling acoustic wave power of is experimentally obtained. It is established that a change in the ultrasonic frequency from 25 to leads to variation in the external Bragg angle in the range from to . At a fixed Bragg angle the frequency band of diffraction is and the angular range of laser beam scanning reaches . The results obtained indicate that AO interaction can be used for controlled deflection of electromagnetic THz beams.