We demonstrate flexible performance in a fiber MOPA system based on nLIGHT’s PFL seed laser platform and chirally coupled core (3C®) fiber. The 33μm core, 27μm MFD 3C fiber used in these demonstrations is fabricated in volume at nLIGHT’s Finland facility. A variety of pulse formats are amplified to nonlinearity-limited peak power <300kW, including single pulses in the 50ps to 1ns regime at a variety of repetition rates from 10’s of kHz to MHz. Beam quality in these 3C based MOPAs is exceptional with M2<1.15 and circularity <95% at all power levels. Beam pointing often evident in other LMA fiber technologies due to higher order mode content is minimal in these fiber MOPAs. Burst mode operation of the seed laser system using flexible burst packet repetition rates (10’s of kHz to several MHz) and adjustable pulse-to-pulse spacing within bursts (<10ns to 100ns) is demonstrated and amplified in the same 3C fibers. Bursts of up to ten 50ps pulses amplified to total energies exceeding 160μJ are demonstrated at 200kHz burst repetition rate and 32W average power at high efficiency (74% slope). Bursts of up to five 500ps pulses are also amplified to up to 360μJ total energy. In both cases, the varying degree of pulse saturation win a burst and mitigation paths are reviewed.
We have demonstrated a pulsed 1064 nm PM Yb:fiber laser system incorporating a seed source with a tunable pulse repetition rate and pulse duration and a multistage fiber amplifier, ending in a large core (>650 μm2 mode field area), tapered fiber amplifier. The amplifier chain is all-fiber, with the exception of the final amplifier’s pump combiner, allowing robust, compact packaging. The air-cooled laser system is rated for >60 W of average power and beam quality of M2 < 1.3 at repetition rates below 100 kHz to 10’s of MHz, with pulses discretely tunable over a range spanning 50 ps to greater than 1.5 ns. Maximum pulse energies, limited by the onset of self phase modulation and stimulated Raman scattering, are greater than 12.5 μJ at 50 ps and 375 μJ at 1.5 ns , corresponding to >250 kW peak power across the pulse tuning range. We present frequency conversion to 532 nm with efficiency greater than 70% and conversion to UV via frequency tripling, with initial feasibility experiments showing >30% UV conversion efficiency. Application results of the laser in scribing, thin film removal and micro-machining will be discussed.