Transmitting volume Bragg Gratings in PTR glass written with femtosecond Bessel beams

摘要

Transmitting volume Bragg gratings were fabricated in photo-thermo-refractive glass using femtosecond laser Bessel beams and thermal treatment. The phase contrast images of gratings under different writing power were investigated before and after annealing. Microstructures composed of nano-sized crystals were observed in the exposed regions. Optimized writing power (100 mW) achieved dense nano-crystals distribution. A maximum diffraction efficiency of 92.36% was achieved with 1 mm grating thickness at period of 5 µm.