High-Repetition-Rate, Single-Pass Third-Harmonic Generation of 354 nm Ultraviolet Laser with 51.5% Efficiency

At a high repetition rate of 1 MHz, the maximum 32.1 W TEM00 mode ultraviolet (UV) laser is generated by harmonically converting the output of semiconductor-diode-seeded four-cascaded fiber amplifiers. The master-oscillator-fiber-power-amplifier (fiber-MOPA) configuration based IR source exhibits high power with excellent spatial, temporal, spectral, and polarizing performances. The novel single-pass frequency tripling scheme, beginning with the noncritical phase matching (PM) for second-harmonic generation and the subsequent noncollinear PM for third-harmonic generation, is used to minimize the spatial walk-off effect. Due to the overall system optimization, the optic–optic conversion efficiency from IR to UV is scaled up to 51.5%.