Local quasi-phase matching improvement method for multi-point focusing frequency doubling process

Abstract

The invention discloses a local quasi-phase matching improvement method for the multi-point focusing frequency doubling process, is improved on the basis of local quasi-phase matching (LQPM) and can provide better phase matching for the multi-point focusing process. The method is specifically characterized in that the phase relationship between adjacent matching points is considered, an original LQPM superlattice structure design function is corrected by adding a coupling phase term, mutual interference of the adjacent matching points in the secondary harmonic propagation direction is suppressed, moreover, harmonic conversion efficiency of the nonlinear process is improved. The LQPM improved method can further be considered as a method of generating nonlinear beam shaping, through design of the superlattice domain structure, frequency conversion and secondary harmonic wavefront modulation can be simultaneously realized, and the secondary harmonic propagation trajectory can be arbitrarily designed and is not limited to common beams such as the Airy beam. The method is advantaged in that focusing accuracy and frequency doubling conversion efficiency of frequency doubling dense focusing are improved, and important applications in improving nonlinear optical imaging quality and beam quality are achieved.

Description

technical field [0001] The invention belongs to the field of nonlinear optics, and specifically relates to phase matching technology in the field of nonlinear optical modulation. The generation, deflection, and controllable focusing of frequency-doubled waves are realized by optical superlattices. Related technologies of manual design and modulation of frequency distribution. Background technique [0002] The nonlinear optical process refers to the frequency conversion process of strongly coherent light entering the nonlinear optical medium, including frequency doubling, sum frequency, and difference frequency processes. Generally speaking, natural nonlinear crystals have dispersion effects, which make the phases of harmonics at different positions in the material different, and coherence enhancement cannot occur. This phenomenon is known as phase mismatch, and phase mismatch makes nonlinear optical processes very inefficient. [0003] The quasi-phase matching technique (Q...

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