Nanosecond laser damage characteristics of multilayer dielectric films and gratings

Multilayer dielectric gratings (MLDGs) have been widely used as pulse compression grating (PCG) in chirped pulse amplification (CPA) technology due to their high laser induced damage thresholds (LIDTs). The quest for MLDGs LIDTs improvement is endless. As one of the core components of CPA process, MLDGs will encounter laser irradiation of nanosecond, picosecond and femtosecond. Therefore, the damage characteristics of MLDGs should be studied at various pulse widths. We performed the LIDTs test on a Nd:YAG laser system with a wavelength of 1064 nm and a pulse width of 8 ns. Damage characteristics of both MLDFs and MLDGs were investigated. MLDFs were deposited on the substrates cleaned by hand wipe or ultrasonic cleaning. The results show that the LIDTs of MLDGs are approximately 60% of MLDFs. Besides, LIDTs of MLDFs with HfO2 top layer will not be affected by the methods of substrates cleaning due to its surface damage characteristic related to the non-zero EFI on the surface material. However, for the MLDFs with top layer of Ta2O5, LIDTs of MLDFs deposited on substrates cleaned by hand wipe are higher than those deposited on the ultrasonically cleaned substrates.