1 College of Electric Power, North China University of Water Resources and Electric Power, Zhengzhou 450045, China;
2 College of Surveying and Geo-informatics, North China University of Water Resources and Electric Power, Zhengzhou 450045, China;
3 College of Precision Instrument and Opto-electronics Engineering, Institute of Laser and Opto-electronics, Tianjin University, Tianjin 300072, China
Abstract High-efficiency terahertz (THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation (OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically poled lithium niobate (PPLN) part and an aperiodically poled lithium niobate (APPLN) part. Two infrared pump waves with a frequency difference ω T1 generate THz waves and a series of cascaded optical waves in the PPLN part by cascaded difference frequency generation (CDFG). The generated cascaded optical waves with frequency interval ω T1 then further interact in the APPLN part by OCDFG, yielding the following two advantages. First, OCDFG in the APPLN part is efficiently stimulated by inputting multi-order cascaded optical waves rather than the only two intense infrared pump waves, yielding unprecedented energy conversion efficiencies in excess of 37% at 1 THz at 100 K. Second, THz waves with M times ω T1 are generated by mixing the mth-order and the (m+M)th-order cascaded optical waves by designing poling period distributions of the APPLN part.
(Frequency conversion; harmonic generation, including higher-order harmonic generation)
Fund: Project supported by the National Natural Science Foundation of China (Grant Nos. 61735010, 31671580, and 61601183), the Natural Science Foundation of Henan Province, China (Grant No. 162300410190), and Program for Science &Technology Innovation Talents in Universities of Henan Province, China (Grant No. 18HASTIT023).
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