Laser Damage Resistance of Photo-Thermo-Refractive Glass Bragg Gratings

Thick Bragg gratings recorded in the volume of photo-thermo-refractive (PTR) glass have found wide application in high-power laser beam control. They have been successfully used for spectral beam combining, angular magnifying for beam scanning, selection of transverse and longitudinal modes in laser resonators etc. Laser damage was studied in PTR glass blanks and gratings fabricated under different conditions. No threshold reduction was found after grating recording in PTR glass. The laser damage threshold of a volume Bragg grating for a single mode 1 ns pulse at 1054 nm focused on inclusions was 7 J/cm, while irradiation of inclusion-free sites resulted in surface damage at 20 J/cm. N-on-1 laser damage tests 1 for 10 Hz repetition rate 1064 nm multimode 8 ns pulses focused to a 78 μm diameter spot have shown a 32 J/cm threshold for a Pt-melted sample with detected inclusions, and a surface damage threshold greater than 42 J/cm for a sample with no detected Pt-inclusions.