An all-fibre PM MOPA pumped high-power OPO at 3.82 microns based on large aperture PPMgLN

We report a large aperture PPMgLN based OPO generating 21W of average output power at a slope efficiency of 45%, pumped by the output from a polarization maintaining Ytterbium doped fiber MOPA operating at 1060nm producing 58W of average output power and 20ns pulses at a repetition rate of 100kHz. A maximum of 5.5W of optical power was recorded at the idler wavelength of 3.82µm without thermal roll-off. We have experimentally verified that the pulse rise/fall time plays a significant role in the OPO conversion efficiency and that further enhancement in the OPO conversion efficiency will be possible using sub-nanosecond rise and fall times

Green-pumped, picosecond MgO:PPLN optical parametric oscillator

We investigate the performance of a magnesium-oxide-doped periodically poled lithium niobate crystal (MgO:PPLN) in an optical parametric oscillator (OPO) synchronously-pumped by 530nm, 20ps, 230MHz pulses with an average power of up to 2W from a frequency-doubled, gain-switched laser diode seed and a multi-stage Yb:fiber amplifier system. The OPO produces ~165mW (signal, 845nm) and ~107mW (idler, 1421nm) of average power for ~1W of pump power and can be tuned from ~800nm to 900nm (signal) and 1.28µm to 1.54µm (idler). Observations of photo-refraction and green-induced infrared absorption (GRIIRA) in different operational regimes of the MgO:PPLN OPO are described and the role of peak intensity and average power are investigated, both with the aim to find the optimal operating regime for pulsed systems

Picosecond Fiber MOPA Pumped Supercontinuum Source With 39 W Output Power

We report a picosecond fiber MOPA pumped supercontinuum source with 39 W output, spanning at least 0.4-2.25 µm at a repetition rate of 114.8 MHz. The 2m long PCF had a large, 4.4 µm diameter core and a high-delta design which led to an 80% coupling efficiency, high damage threshold and rapid generation of visible continuum generation from the picosecond input pulses. The high and relatively uniform power density across the visible spectral region was ~31.7 mW/nm corresponding to peak power density of ~12.5 W/nm for the 21 ps input pulses. The peak power density was increased to 26.9 W/nm by reducing the repetition rate to 28 MHz. This represents an increase in both average and peak power compared to previously reported visible supercontinuum sources from either CW pumped or pulsed-systems

Pulse energy packing effects on material transport during laser processing of < 1

The effects of energy pulse packing on material transport during single-pulse laser processing of silicon is studied using temporarily shaped pulses with durations from 50 to 150 ns. Six regimes of material transport were identified and disambiguated through energy packing considerations over a range of pulse durations. Energy packing has been shown to shift the interaction to energetically costlier regimes without appreciable benefit in either depth, material removal or crater morphology and quality.The authors would like to thank the UK Technology Strategy Board under project TP14/HVM/6/I/BD5665. The authors acknowledge the EPSRC Centre for Doctoral Training in Photonic Systems Development for their generous support

A fiber based synchronously pumped tunable Raman laser in the NIR

Raman lasers have attracted much interest since they allow a very wide range of wavelengths to be generated [1]. Operation in the pulsed regime is compromised by the power dependence of the gain - different parts of the pulse with different instantaneous power will undergo differing amounts of Raman scattering leading to major variations in spectral content across the pulse (varying amounts of light in different Raman orders). To address this issue active pulse shaping technique can be applied to obtain rectangular shaped output pulses so that constant Raman gain can be ensured across the pulse profile [2]. Here we demonstrate a new approach combining pulse shaping with a synchronously pumped scheme [3] to produce narrower linewidths as well as higher extinction ratios between neighboring Raman Stokes lines. Several tens of nanometer of tuning range for each Stokes order and a total tuning range of over 200 nm was achieved using resonant feedback from an external bulk grating

Externally modulated diode seeded Yb³⁺- doped fiber MOPA pumped high power optical parametric oscillator

Here we report a high power, pulsed optical parametric oscillator (OPO) at 3.5µm by using a MgO:PPLN crystal as the gain medium. The OPO itself was pumped by a semiconductor diode-seeded, Yb3+-doped fiber Master Oscillator Power Amplifier (MOPA) operating at 1062nm. An OPO output power as high as 11W at an overall slope efficiency of 67% was achieved, with nearly 2.7W and 8.2W of optical power obtained at 3.5µm and 1.5µm respectively. Due to the fast response time of the external modulator, it is possible to implement active pulse shaping on a nanosecond time-scale. Using adaptive pulse shaping of the seed laser (using an external modulator) we demonstrated a reduction in the impact of dynamic gain saturation and optical Kerr/Raman nonlinearities within the fibre MOPA obtaining shaped signal and idler pulses at the OPO output and reduced spectral bandwidths. We have also investigated the dependence of the OPO build-up time and energy transfer efficiency on pump pulse peak power and shape. The build-up time shows an exponential dependence on the pulse peak power and as expected decreases with an increase in pulse peak power. Analyzing the shift in spectral peak at 1.5µm it is possible to estimate the internal temperature of the crystal for various pump powers. Our experiments were pump-power limited and considerable scope remains for further power-scaling of the OPO output using this approach

56W frequency doubled source at 530 nm pumped by a single-mode single-polarization picosecond Yb³⁺-doped fiber MOPA

We report a frequency doubled green source at 530nm pumped based on an all-fiber, picosecond, single polarization Yb3+-doped fiber MOPA delivering 20ps pulses at user selectable repetition rates of up to 910MHz and an average output power in excess of 100W at 1.06µm. The output of the MOPA was frequency doubled using a LBO crystal. Up to 56 W of green light was generated at a corresponding repetition rate of 227 MHz at an overall conversion efficiency of 56%. The diode-to-green optical power conversion efficiency was 37%