Physical model and analysis of spectral beam combining system with dual-grating external cavity

Spectral beam combining (SBC) has the potential to further increase the power irrespective of the limited power of single laser, and to maintain the near-diffraction-limited beam quality. However, the total power, the beam quality, and the spectra of SBC are significantly affected by the crosstalk effect attributed to the "smile" effect. Although crosstalk mitigation methods have been proposed, with the increasing laser number in dense spectral beam combining, the crosstalk caused by the spectral dispersion of single laser may hinder the further improvement of SBC. Fortunately, SBC with a dual-grating external cavity has shown the potential to narrow the linewidth of the laser array. However, its physical model has not been previously reported, restricting the comprehensive understanding of the system. Here, we present the physical model of SBC with the dual-grating external cavity. Using this physical model, the mitigation of spectral dispersion in single laser by the dual-grating configuration is investigated in depth. The influence of grating parameters on the combined beam, including its spectra and beam quality, is also analyzed. Furthermore, the alignment of the dual-grating, significantly affecting the beam quality and spectra of the combined beam, can be used for system optimization. We hope this model can provide valuable insights and guidance to the spectral dispersion management in SBC.