Conversion of coherent infrared radiation into millimeter waves in a waveguide with a GaAs crystal

A description is given of the apparatus used to observe and study the frequency conversion of coherent infrared radiation (λ = 10.6 μ) into millimeter waves (λ = 5.5 mm). In these experiments the radiation of a CO₂ laser emitting pulses at several frequencies is mixed to produce a wave at difference frequency in a waveguide filled with a nonlinear GaAs crystal. Information is given on the observed difference frequencies and on the shape of the final signal. Calculations and experimental results are reported for the dependence of the amplitude of the final signal on the direction of polarization of the laser radiation and various orientations of the GaAs crystal.