Abstract
We report a 5.8-W deep-ultraviolet (DUV) laser obtained from frequency-quadrupling of an all-fiberized ytterbium-doped fiber (YDF) master oscillator power amplifier (MOPA). The MOPA system delivers 585 ps pulses at 1040 nm with a maximum available output power of 23.5 W for nonlinear frequency conversion. A lithium triborate (LBO) crystal and a beta barium borate (BBO) crystal are employed for second- and fourth-harmonic generation (FHG), respectively. At a repetition rate of 1.6 MHz, a maximum DUV output power of 5.8 W is obtained at 260 nm with a corresponding pulse energy of 3.6 μJ and maximum peak power of at least 6.9 kW. A 1μm-to-260nm conversion efficiency of 26.4% is achieved at a DUV output power of 5.8 W. To the best of our knowledge these results represent the highest-average-power fiberized-laser-pumped DUV laser, as well as the most efficient DUV generation based on BBO crystals to date. We further demonstrate application of the pulsed DUV laser in bacterial disinfection achieving an inactivation efficiency of 99.999% for E-coli bacteria at a DUV exposure of 7 mJ/cm2.
Highlights
High-power pulsed DUV lasers with high photon energy have various applications in photolithography [1], material processing [2], spectroscopy [3], and biomedicine [4]
Good-quality nonlinear crystals are vitally important for harmonic DUV generation and only a few suitable and commercially available crystals have been developed over the years, such as barium borate (BBO), caesium lithium borate (CLBO), and potassium beryllium fluoroborate
When the pump power was more than 15.5 W, the second-harmonic generation (SHG) power and conversion efficiency started to roll-off due to back-conversion
Summary
High-power pulsed DUV lasers with high photon energy have various applications in photolithography [1], material processing [2], spectroscopy [3], and biomedicine [4]. YDF lasers have attracted great attention in particular owing to their compact nature, high output power, high efficiency and reliability, good beam quality, and suitability for simple air-cooling. Good-quality nonlinear crystals are vitally important for harmonic DUV generation and only a few suitable and commercially available crystals have been developed over the years, such as BBO, caesium lithium borate (CLBO), and potassium beryllium fluoroborate. BBO and CLBO are the most commonly used crystals for high-power DUV laser development due to their high nonlinear coefficients, high laser damage thresholds and mature growth techniques. Compared with CLBO, BBO with a lesser hygroscopic susceptibility and larger nonlinear coefficients is the more favorable choice for high-power, long term DUV operation
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