Robust 5 W continuous-wave 355 nm laser by single-pass third harmonic generation in LBO crystals

A high-power, narrow-linewidth, continuous-wave 355 nm laser based on single-pass third-harmonic generation of a fiber laser in two LBO crystals is presented. Both type I and type II critical phase-matching in LBO crystals was investigated for the sum-frequency generation stage. A maximum output power of 5 W with a root-mean-square power stability of 0.73% was achieved by using a type-I critical PM LBO crystal, with a single-pass conversion efficiency of 1.7% from 1064 nm to 355 nm. The relative intensity noise of the 355 nm laser was below -110 dB/Hz in the frequency range above 200 Hz. Such a single-pass THG laser system, with its compact architecture and robustness, has great potential for applications in semiconductor manufacturing and inspection.