Piezoelectric Ultrasonic Harmonic Generation in Cadmium Sulfide

Theory and experiment are presented for the strong acoustic harmonics produced in photoconductive cadmium sulfide as a result of nonlinearities in the electron-lattice interaction responsible for ultrasonic amplification. Data have been taken at fundamental shear-wave frequencies of 11.5 and 30 Mc on a 7-mm crystal and at 30 Mc on a 3-mm crystal. The second-harmonic output was measured as a function of input power at the crossover point (where the electron drift velocity is equal to the sound velocity) for various sample resistivities. The harmonic power is shown to be proportional to the square of the input power, and the largest harmonic obtained was 4 dB below the fundamental for an input acoustic intensity of approximately 1 W/${\mathrm{cm}}^2$.