Artser Ilya, Melnik Maksim, Ismagilov Azat, Guselnikov Mikhail, Tcypkin Anton, Kozlov Sergei
International Laboratory of Femtosecond Optics and Femtotechnologies, ITMO University, St. Petersburg, Russia.
Sci Rep. 2022 May 30;12(1):9019. doi: 10.1038/s41598-022-13445-1.
High-intensity optical radiation propagation in a transparent dielectric medium causes the phenomena of pulse self-action and radiation generation at triple frequencies due to the cubic nonlinearity of the medium. However, quadratic nonlinear effects usually outshine the cubic ones in anisotropic nonlinear crystals. In this work, we demonstrate that for certain experimental parameters the nonlinear effect of the third order can be stronger than the second order one in the MgO:[Formula: see text] crystal for terahertz frequency range. We experimentally and theoretically show that this effect can lead to the significant modification of the classical phenomenon of radiation generation at triple frequencies in the case when the pulse represents only one complete oscillation of the optical field. The experiment demonstrated that the phenomenon of generation of radiation at triple frequencies with respect to the frequency of the maximum spectral density in a nonlinear medium of the pulse disappears, and it is replaced by the generation of radiation at quadruple frequencies. The analysis confirms that this effect is based on the asymmetry and large width of the initial spectrum of such extremely short pulses in terms of the number of oscillations.
高强度光辐射在透明电介质中传播时，由于介质的立方非线性，会导致脉冲自作用现象以及三倍频辐射产生。然而，在各向异性非线性晶体中，二次非线性效应通常比立方非线性效应更为显著。在这项工作中，我们证明，对于某些实验参数，在太赫兹频率范围内，MgO:[公式：见原文]晶体中的三阶非线性效应可能强于二阶非线性效应。我们通过实验和理论表明，当脉冲仅代表光场的一次完整振荡时，这种效应会导致三倍频辐射产生这一经典现象发生显著改变。实验表明，在脉冲的非线性介质中，相对于最大光谱密度频率的三倍频辐射产生现象消失，取而代之的是四倍频辐射产生。分析证实，这种效应是基于此类极短脉冲初始光谱在振荡次数方面的不对称性和较宽宽度。
