6 MW peak power UV microlaser using novel pumping

High peak power, 355 nm ultraviolet (UV) short-pulse lasers are very useful for many applications, such as, materials processing and 3D printing. However, such applications are limited by the size and cost of UV lasers. We report the design and fabrication of a > 6 MW peak power, very compact and cost-effective 355 nm UV microlaser. We used a specially designed Nd:YAG/ Cr4+:YAG microchip laser pumped through a fiber combiner. The in-house fabricated fiber combiner enabled a compact design using several low-cost/low-power, air-cooled laser diodes to pump the microchip laser, without sacrificing pump beam quality needed for end-pumping. The microchip laser used a [100]-cut Nd:YAG with an undoped YAG end-cap as the gain medium. This enabled high output power without depolarization, which is essential for high efficiency wavelength conversion. A low initial transmission Cr4+: YAG was used as the passive Q-switch to obtain high peak power. We achieved 11.3 mJ pulse energy, 935 ps pulse width, >12 MW peak power with good beam quality at 1064 nm, without using a MOPA system. Third harmonic generation was performed by sum-frequency generation using Type I and Type II LBO crystals. We achieved 4.1 mJ pulse energy, 645 ps pulse width, resulting in 6.36 MW peak power at 355 nm. The conversion efficiency from 1064 nm to 355 nm was 52%. These are the highest pulse energy and peak powers achieved at 355 nm using a compact microchip laser. Our low-loss fiber combiner design for pumping is scalable, to further increase the output power.