High-Power Near Flat-Top Distributed Ultraviolet 330 nm Laser for Photochemical Synthesis

We demonstrate a 10-watt level nanosecond pulse ultraviolet (UV) 330 nm laser from a two-stage cascaded second harmonic generation (SHG) of 1319 nm Nd:YAG laser. The diode-side-pumped Nd:YAG oscillator at 1319 nm is operated in the Q-switched macro/micro pulse regime, which is beneficial for increasing the average output power of the fundamental wave. In order to further scale the 330 nm output power, two LBO crystals rotated by 180° are employed to compensate for the spatial walk-off effect in the second-stage SHG configuration. Consequently, a record-high average output power of 11.9 W at 330 nm is achieved with total nonlinear conversion efficiency up to 33.1% from infrared to UV. Moreover, the UV circular beam with Gaussian spatial mode is homogenized and reshaped by two pairs of orthogonal cylindrical microlens arrays. Then, a near flat-top distributed square beam with adjustable spot size is realized, which helps to avoid absorption saturation and improve the reaction efficiency in photochemical synthesis.