Optical Breakdown in Fused Silica and Argon Gas: Application to Nd:YAG Laser Limiter

A gas cell filled with argon gas under pressure is placed in a tightly focused laser beam to provide a limiter for laser pulses above a certain peak power, corresponding to the optical breakdown threshold for the creation of a laser-induced plasma. Measurements of the threshold intensity as a function of argon gas pressure are given for a laser wavelength of 1.064 (mu)m (Nd:YAG) and a pulse length of 6.4 ns. Threshold intensities for optical breakdown in fused silica were measured with the same optical system, enabling a relative comparison of breakdown thresholds, of interest for protecting fused-silica optical components in fiber-optic delivery systems for laser material processing applications. The threshold intensity was measured to 220 GW /cm2 in Ar at 1.0 x 105 N /m2 (1 atm), 80 GW /cm2 in Ar at 8.0 x 105 N /m2 (7.9 atm), and 55 GW /cm2 in fused silica. Even though the threshold in argon is higher than that in fused silica, the limiter will protect the optical components if the laser beam is focused to a tighter spot in the gas cell than at the input end of the fiber. [Optical Society of America ]