The broadband high efficiency fourth harmonic generation (FHG) of lasers cannot only be used as the optical probe of physical diagnostics, but also has the probability of directly interacting with the nuclear target in ICF instead of third harmonic generation (THG) lasers widely used at present. Shorter wavelength lasers increase the energy absorption efficiency, and suppress stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS). Many effective technology methods have been used for the phase matching of broadband pulses, such as achromatic phase matching, chirp matched harmonic generation, multi-crystals design, quasi phase matching, retracing point phase matching, etc. However, the non-collinear phase matching technology is relatively a new study direction for its free geometry configuration, and it can be used in the pre-focusing scheme to get higher damage threshold.

In this paper, non-collinear phase matching theory is analyzed firstly, which provides the numerical calculation foundation for non-collinear FHG and FIFHG phase matching angle (NCPMA), effective nonlinear coefficients (ENC), two kinds of angle bandwidths (AB) and wavelength bandwidth (WB) of a 1064nm fundamental laser, using KDP as an example. The optimal angle bandwidth and wavelength bandwidth and the corresponding phase matching angle and effective nonlinear coefficients are numerically calculated in the same procession as FHG of KDP for general nonlinear crystals such as DKDP, ADP, BBO, CLBO, and KBBF.

The results have been published as Dongsheng Song, Yuanlin Zheng, Xiaohui Zhao, Zengyan Cai, and Xianfeng Chen, Bandwidth analysis of non-collinear fourth and fifth harmonic generation in nonlinear uniaxial crystals[J]. Journal of Nonlinear Optical Physics & Materials, 2017.