ИСТИНА

In previous studies [1,2] the problem of sum-frequency generation (SFG) in isotropic chiral medium was considered mostly for the spectroscopy of chiral solutions, when the conversion efficiency of the energy of incident radiation into the energy of radiation at sum-frequency (SF) was low [1]. Nevertheless, it was shown, that two elliptically polarized Gaussian beams propagating coaxially in such a medium generate an inhomogeneously polarized sum-frequency beam [2]. At present time there are artificially created materials (metamaterials) possessing the same symmetry as the isotropic chiral media, and having the efficient values of nonlinear second-order optical susceptibility several orders higher compared to the ‘classical’ media of this kind (e.g., solutions of chiral molecules). In such materials, SFG can be used for the formation of light beams with inhomogeneous transversal polarization distributions controlled by incident beams, and for the design of optical logic elements. However, the undepleted pump approximation (UPA) widely used in theoretical works for the description of the evolution of SF beam now may have limited validity due to high conversion efficiency of SFG in such highly nonlinear materials. We have carried out numerical modeling of three-wave mixing in isotropic chiral medium taking into account the evolution of intensity and polarization of all three propagating waves at fundamental and sum frequencies. The impact of the phase mismatch on the energy conversion efficiency (from fundamental waves to sum-frequency wave) observed in our study is the same, as predicted earlier analytically within the framework of UPA [1]. It is shown that for energy conversion efficiency less than 0.001, the UPA describes the evolution of intensity and polarization of SF beam with good precision (better, than 1%), and the polarization effects predicted earlier [2] are also observed in our numerical modeling. If the conversion efficiency increases up to 0.1, the SF beam cannot be correctly described by the UPA, while the fundamental beams remain almost unchanged. For higher values of conversion efficiency, strong changes of the intensity and polarization of fundamental beams occur, along with complex behavior of SF beam, which was not predicted earlier within the UPA theory framework. Authors acknowledge the support of Russian Foundation for Basic Research, grants No 16-02-00154 and 18-32-00217. [1] N.I. Koroteev, V.A. Makarov,S.N. Volkov, Laser Phys., 9, 655 (1999). [2] S.N. Volkov, V.A. Makarov, I.A. Perezhogin, QuantumElectron., 36, 860 (2006).