Optimization of 1.03μm femtosecond pulse laser tripling efficiency based on temporal walk-off compensation

Ultraviolet (UV) femtosecond lasers with a high repetition rate have important applications, especially in processing brittle materials. However, the group velocity walk-off limits the tripling efficiency of the 1μm femtosecond pulse. Without effective compensation, the tripling efficiency was generally less than 1%. In this study, by optimizing a birefringent BBO crystal to compensate the temporal walk-off in the 1.03μm tripling process, a maximum output power of 1.9 W with a repetition rate of 145 kHz at 344 nm was obtained, which implied a conversion efficiency of 30.5% from infrared (IR) to UV. The generated UV laser showed good power stability of 0.19% rms over 1 h and beam quality of M2 < 1.2. Using this scheme for other IR femtosecond lasers is promising for achieving high tripling efficiency.