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1The 30th International Conference on Advanced Laser Technologies
ALT'23
N-I-18
Prism-lens couplers for efficient sideways Cherenkov terahertz wave
generation in nonlinear crystals
N.V. Starkova1, D.A. Safronenkov1,D.A. Markov1, G.Kh. Kitaeva1
1Lomonosov Moscow State University, Leninskie Gory 1-2, Moscow 119991 Russia
gkitaeva@physics. msu. ru
The ways to increase the power efficiency of the sideways terahertz wave (THz) generation are studied considering Cherenkov optical rectification (OR) scheme in Mg:LiNbO3 crystal. We propose to equip the generating nonlinear crystal with a prism-lens coupler made of high-resistance Si with a specially selected output surface curvature. Experimentally, about 4.5-fold increase in output THz field amplitude (Fig.la) and the 12-fold increase in the detected power at 0.5 THz have been achieved when a common flat-surface prism [1] was supplied by one of plano-convex lenses under investigation.
Time, ps 6, grad 6, grad
(a) (b) (c)
Fig. 1. THz waveforms detected experimentally with the flat Si prism (black dots) and with the same prism supplied by different Si lenses (a); angular distributions of the output THz power calculated for the case of the flat Si prism (b) and the prism-lens coupler
curvature of the output surface (c).
plano-convex with optimal
To explain the demonstrated advantage of the curved coupler's curvatures, we calculated the angular distributions of THz radiation power which are emitted by the crystal parts located at the lens axis (Figs.1b,c). The calculations are based on the general approach, when the THz generation under OR of femtosecond laser pulses unside the nonlinear crystal is considered as a continuous set of simultaneous nonlinear three-wave processes of parametric difference frequency generation [2], and the subsequent transformation of differently directed planar THz components during their propagation through the crystal-Si and Si-air interfaces is taken into account [3]. The developed theoretical approach forecasts new perspective shapes of the Si-adaptor output surfaces and can be used for further design of optimal extraction elements.
The work was done under financial support of the Russian Science Foundation (Grant No. 22-12-00055).
[1] K. Kawase, J. Shikata, and H. Ito, Terahertz wave parametric source, Journal of Physics D: Applied Physics 35, R1 (2002).
[2] G.Kh. Kitaeva, V.V. Kornienko, A.A. Leontyev, and A.V. Shepelev, Generation of optical signal and terahertz idler photons by spontaneous parametric down-conversion, Phys. Rev. A 98, 063844 (2018).
[3] G.Kh. Kitaeva, D.A. Markov, D.A. Safronenkov, N.V. Starkova, Prism couplers with convex output surfaces for nonlinear Cherenkov terahertz generation, Photonics 10, 450 (2023).
