Gratings' rotation angle tolerance for diode lasers with external cavity formed by volume Bragg grating

For high power linewidth-narrowed diode lasers, it's important to study rotation angle tolerance of the volume Bragg grating (VBG) for narrowing the spectral linewidth of two dimensional diode laser stacks. The diode laser with the VBG's external cavity and C-mounted modules is collimated by 200 m and 600 m cylindrical lens separately in the paper. The VBG's angle tolerance is acquired by two stepper motors. According to the research, more accuracy is needed for the VBG's adjustment with higher driving current and better beam collimation. If the laser diode is collimated better in fast axis direction, rotation angle tolerance in slow axis direction will be bigger. When a VBG with a diffraction efficiency of 28% and thickness of 1.4 mm is used to lock the wavelength of a laser diode with a fast axis divergence angle of 7.3 mrad, the grating's rotation angle tolerance is no more than 3.2 mrad in the fast axis direction and that for the slow axis direction is one order of magnitude bigger.