期刊
APPLIED SCIENCES-BASEL
卷 13, 期 12, 页码 -出版社
MDPI
DOI: 10.3390/app13127341
关键词
nonlinear optics; harmonic generation; ultraviolet generation; frequency tripling
We propose using cascaded second-harmonic generation (SHG) to achieve frequency conversion in a way similar to that in a medium with cubic susceptibility. By introducing phase mismatching, we can efficiently generate third-harmonic waves. Theoretical predictions suggest a THG efficiency of 94.5%.
Third-harmonic generation (THG) is of interest for its various applications. We propose using the cascaded second-harmonic generation (SHG) to implement the frequency conversion process, which is similar to that occurring in a medium with cubic susceptibility. Physically, the process is based on consecutive generation of the second-harmonic and the sum frequency in the same crystal with quadratic susceptibility at large phase mismatching between the fundamental wave and the second-harmonic wave. In this case, at phase matching between the fundamental wave and the third-harmonic wave, THG occurs with high efficiency. To demonstrate such a possibility theoretically, we apply the multi-scale method to a set of Schrodinger equations, describing a three-wave interaction with the frequencies ?,2? and 3? in a medium with quadratic susceptibility, to derive modified equations describing the frequency tripling process. These equations are solved without using the fundamental wave energy non-depletion approximation. A THG efficiency equal to 94.5% is predicted theoretically. The analytical solution is confirmed by computer simulation results. We study how various factors, such as the incident pulse intensity, phase mismatching between interacting waves, group velocity mismatching of the pulses, and second-order dispersion of the wave packets influence the THG process.
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