We report on an 888 nm pumped passively mode-locked TEM(00)Nd:YVO(4) oscillator providing 56 W of average power at a repetition rate of 110 MHz with 33 ps pulse duration, further amplified to 111 W in a 52% optical efficiency single-pass amplifier stage, maintaining beam quality at M(2)=1.05. Frequency doubling in a LiB(3)O(5) crystal generated up to 87 W at 532 nm, while a third harmonic power of 35 W was achieved in a nonoptimized tripling configuration, corresponding to 80% and 33% conversion efficiency.
We propose a technique for pumping Nd:YVO(4) with high optical power at 888nm while making absorption independent of the pump light polarization state. This is especially suitable for systems end pumped by high-power, high-brightness fiber-coupled diode sources associated with long vanadate crystals to effectively spread the heat load in a large volume. A compact 60 W output, 55% optical efficiency cw TEM(00) oscillator was demonstrated.
High-precision micromachining with picosecond lasers became an established process. Power scaling led to industrial lasers, generating average power levels well above 50 W for applications like structuring turbine blades, micro moulds, and solar cells. In this paper we report, how a smart distribution of energy into groups of pulses can significantly improve ablation rates for some materials, also providing a better surface quality. Machining micro moulds in stainless steel, a net ablation rate of ~1 mm³/min is routinely achieved, e.g. using pulse energy of 200 µJ at a repetition rate of 200 kHz. This is industrial standard, and demonstrates an improvement by two orders of magnitude over the recent years.When the energy was distributed to a burst of 10 pulses (25 µJ), repeated with 200 kHz, the ablation rate of stainless steel was 5 times higher with the same 50 W average power. Bursts of 10 pulses repeated with 1 MHz (5 µJ) even resulted in an ablation rate as high as 12 mm³/min. In addition, optimized pulse delays achieved a reduction of the surface roughness by one order of magnitude, providing Ra values as low as 200 nm. Similar results were performed machining silicon, scaling the ablation rate from 1.2 mm³/min (1 pulse, 250 µJ, 200 kHz) to 15 mm³/min (6 pulses, 8 µJ, 1 MHz). Burst machining of ceramics, copper and glass did not change ablation rates, only improved surface quality. For glass machining, we achieved record-high ablation rates of >50 mm³/min, using a new state-of-the-art laser which could generate >70 W of average power and repetition rates as high as 2 MHz
Efficient frequency conversion of cw mode-locked Ti:A1(2)O(3) laser radiation using lithium triborate, beta-barium borate, and lithium iodate crystals as the nonlinear material is demonstrated. Second-, third-, and fourth harmonic generation results in tunable blue and ultraviolet radiation down to 205 nm with transform-limited pulses and pulse lengths below 1 ps. Maximum average powers (repetition rate 82 MHz) of 700 mW at 400 nm, 120 mW at 272 nm, and 10 mW at 210 nm were obtained. The effects of group-velocity dispersion have to be taken into account to optimize the different frequency-conversion processes.
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