We demonstrate 30 W of average UV power, at 353 nm, by harmonically converting the output of a seeded
cascade of fiber amplifiers operating at 1060 nm. The UV output represents 46% harmonic conversion
efficiency from the fundamental beam. The all-fiber-amplifier, MOPA architecture supports variable pulse
repetition frequencies and pulse widths. We demonstrate pulse repetition frequencies up to 2 MHz and
pulse widths as short as 2 ns. Two bulk LBO crystals, oriented for second and third harmonic conversion,
are used to obtain stable UV output power. A turnkey system using this architecture is commercially
available. The system is entirely air-cooled and operates from a standard wall plug electric service,
facilitating integration into various material processing applications.
The trend in micro-machining lasers is toward greater average power and higher repetition rate, in order to increase throughput, with pulse energy and peak power held roughly constant, as determined by the small scale of the feature. At repetition rates beyond 500 kHz, conventional high-power Q-switched Nd lasers will reach fundamental limits. We demonstrated a fiber-based oscillator-amplifier architecture which produces pulse repetition rates in the 0.5 - 5 MHz range and pulse durations in the 0.5 - 1.5 nsec range. The oscillator is a compact (35 cm3 package) passively Q-switched Nd:YVO4 laser oscillating at a single frequency. By amplifying this laser in fiber, we demonstrated 10-W average power at the two wavelengths of 914 nm and 1064 nm. At 1064-nm, Yb-doped large mode area fiber will allow scaling of average power to over 100 Watts, with peak power of tens of kW, in a diffraction-limited beam. Excellent conversion will be possible to visible and UV using the robust nonlinear material LBO. By opening up a new range of repetition rates and pulse lengths, at IR, visible and UV wavelengths, in a high power design that has the packaging and efficiency advantages of fiber, new micro-machining applications may be enabled.
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