Improving Beam Quality Of Diode Laser Array By Volume Bragg Grating External Cavity

Characterized by higher power, higher efficiency , smaller size, and longer operating lifetime than any other laser type, Diode laser array (DLA) have applied in many field such as communication, medical care, pumping solid-state lasers and fiber lasers, and other fields. Especially in material processing field, high-power diode laser arrays are growing at a high speed. It is possible for DLA to replace traditional solid-state lasers. But it also faces a number of challenges in terms of beam quality improvement, as the shortcoming of poor coherence seriously limits its further application. These years, it has been proved that volume bragg grating is very useful in improving beam quality of DLA. So a series theoretical and experimental research about improving beam quality based on volume bragg grating as external cavity have been studied in this paper.The transmission of beam through grating is analyzed in accordance with Kogelnik's theory. And diffraction efficiency mode of volume bragg grating is established, wavelength selection and angular selection are obtained. According to diffraction efficiency equation of grating, we obtain the relationship of the parameters described character of VBG, and it can be used to design a proper RVBG.Based on VBG theory, VBG-cavity stabilization DLA spectrum is analyzed theoretically. And DLA consisted of 49 emitters is locked by volume bragg grating in the experiment producing a center wavelength of 807.5 nm and Full-Width Half-Maximum of locked spectrum of 0.4 nm. And the stable spectrum doesn't change with the heat sink temperature and the current drift. A theory mode of phase-lock based on VBG-cavity is established, and it is proved experimentally.In the last part of paper, spectral beam combining of DLA locked by a wavelength-chirped VBG is studied and improved. The spectrum width is 15nm with each emitter of 0.8nm locked by the VBG, which is narrowed notably And the spectrum doesn't change with the heat sink temperature and the current drift. The output power of 24.1W is obtained after beam combining at the injection current of 40A with slope efficiency of 0.76W/A and combining efficiency of about 70%. Beam quality of main beam is about 32 correspondence to single emitter.