A possible room temperature terrahertz wave source via harmonic generation in a microwave pumped ferroelectric crystal

This paper explores theoretically a model for harmonic generation in ferroelectric crystals which, being resonant in the far infrared will also respond to microwave frequencies. The essential idea is that frequency doubling or tripling of microwave radiation incident on the ferroelectric brought about by second or third harmonic generation will produce waves in the terahertz region. The strong response and nonlinearities of ferroelectric crystals in their interaction with microwaves of frequencies of in the range 200 to 300 GHz makes this a viable proposal. Landau-Devonshire theory has been used to calculate nonlinear susceptibility coefficients. Here susceptibility coefficients for second and third harmonic generation are given and it is shown how the slowly varying amplitude (SVA) approximation together with a susceptibility coefficient to solve the wave equation that describes the propagation of the generated waves in the crystal. Conditions on the length through which the waves travel that optimize the phase matching are a useful result of this analysis.