Terahertz pulse induced femtosecond optical second harmonic generation in transparent media with cubic nonlinearity

2020 
Second harmonic (SH) generation of femtosecond laser radiation induced by a short terahertz pulse in a layer of isotropic medium with cubic nonlinearity was investigated. A comprehensive 1D theory of SH field dynamics with allowance for different propagation velocities of interacting terahertz, fundamental, and SH pulses was developed. In particular, it was shown that for media with a coherent length of the fundamental and second optical harmonics smaller than the walk-off length of the fundamental optical and THz pulses, a SH radiation signal is generated only when the fundamental optical and terahertz pulses overlap near the entrance and exit surfaces of the nonlinear layer rather than when the pulses are superimposed in the bulk. The prediction was verified experimentally by using a 3-mm-thick fused quartz. Good agreement between the theory and the experiment was demonstrated.
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