We report the generation of continuous-wave (cw) tunable mid-infrared (mid-IR) radiation across 4608-4694 nm with multi-tens of mW level output power using difference-frequency-generation (DFG) in the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). A 40-mm-long OP-GaP (Λ=85.1 μm) is used for DFG, pumped with a cw Tm-fiber laser and a home-built cw Yb-fiber-pumped MgO:PPLN-based optical parametric oscillator (OPO). By varying MgO:PPLN crystal temperature and simultaneously adjusting the phase-matching temperature in OP-GaP, with an input pump power of 34 W at 2010 nm and OPO idler power of >2.9 W across 3505-3557 nm, we achieved DFG tuning across 4608-4694 nm, providing >30 mW of output power across 96% of the full tuning range with 43 mW at 4608 nm. The output at 4608 nm exhibits high beam quality, with a passive power stability of 2.5% rms over 1.5 mins. The performance of the system at high pump powers, temperature acceptance bandwidth, DFG spectral characteristics, and spatial quality has been investigated.
We report implementation of compact cascaded multicrystal scheme for single-pass second-harmonic-generation (SHG), using birefringent crystal, for continuous-wave (cw) deep ultraviolet (UV) generation. The system comprises of 4 cascaded stages, is based on critical phase-matched interaction in β-BaB2O4 (BBO), and pumped by a cw singlefrequency green source at 532 nm. A deep-UV cw output power of 37.7 mW at 266 nm has been obtained with a high passive power stability of 0.12 % rms over more than 4 hours in Gaussian spatial beam quality with a circularity of >70%.
We demonstrate a high-power fiber-laser-based source of continuous-wave (cw), linearly-polarized radiation at 970 nm
in a simple, compact, and practical design. Using direct single-pass second-harmonic-generation (SP-SHG) of a cw
thulium fiber laser at 1940 nm in a 40-mm-long periodically-poled LiNbO3 (PPLN) crystal, we have generated 13.1 W of
output power at 970 nm for a fundamental power of 40 W. We achieved conversion efficiency as high as 32.7%. The
generated second-harmonic output exhibits a passive power stability better than 1.4% (1σ value) over 1 hour, has a
linewidth better than 0.3 nm, and a TEM00 spatial beam profile with M2<1.6. We further performed relevant theoretical
calculations for the characterization of SP-SHG in the crystal.
We demonstrate the use of an antiresonant ring (ARR) interferometer for optimum output coupling in a continuous-wave
singly-resonant optical parametric oscillator (SRO). The cw SRO, based on a 50-mm-long MgO:PPLN crystal in a
standing-wave cavity, is pumped by cw Ytterbium fiber laser at 1064 nm. The ARR interferometer is integrated into one
arm of the SRO cavity. By fine adjustment of the ARR transmission, a continuously variable signal output coupling from
0.8% to 7.3% has been achieved, resulting in an optimum output coupling of ~4.6% for 23.2 W of input pump power. At
this output coupling, the SRO provides 2.28 W of signal, together with 2.95 W of idler, for 23.2 W of pump power. We
also show that the deployment of the ARR does not lead to any degradation in the output beam quality from the cw SRO.
The technique provides a proof-of-principle demonstration to determine the absolute output coupling in cw SRO for
which output power and extraction efficiency can be maximized.
We report a novel technique for the generation of mode-locked pulses from a continuous-wave (cw) optical parametric
oscillator (OPO). The technique is based on the deployment of an electro-optic phase modulator (EOM) in combination
with an antiresonant ring (ARR) interferometer internal to a cw OPO. The scheme is implemented in a doubly-resonant
cw OPO based on MgO:sPPLT, configured in a standing-wave cavity and pumped at 532 nm by a cw laser. With careful
adjustment of the cavity length, modulation frequency and modulation depth, under different conditions, we achieved
stable train of 730 ps and 450 ps pulses at a repetition rate of 160 MHz and 80 MHz, respectively. At degeneracy,
spectral broadening of ~38 nm and ~20 nm has been observed corresponding to pulses of 160 MHz and 80 MHz
repetition rate, respectively. We have confirmed true mode-locked operation by verifying ~4 times enhancement in
second-harmonic-generation power under mode-locked operation at both 160 MHz and 80 MHz, compared to that in cw
operation, for a fixed average fundamental power.
We report the first experimental demonstration of a high-power Ti:sapphire laser pumped by an efficient, compact and cost-effective continuous-wave (cw) fiber-laser-green source at 532 nm. The green source is obtained by direct singlepass second-harmonic-generation (SHG) of a Yb-fiber laser in MgO:sPPLT crystal, providing 11 W of green power in TEM00 spatial profile. The Ti:sapphire laser is continuously tunable across 743-970 nm and can deliver an output power up to 2.7 W with a slope efficiency as high as 32.8% under optimum output coupling of 20%. The laser output has a TEM00 spatial profile with M2<1.44 across the tuning range and exhibits a peak-to-peak power fluctuation below 5.1% over 1 hour.
We report a simple, compact and novel implementation for single-pass second-harmonic-generation (SP-SHG) of continuous-wave laser radiation based on a cascaded multi-crystal scheme, which can provide the highest conversion efficiency at any given fundamental power. By deploying a suitable number of identical 30-mm-long MgO:sPPLT crystals in a cascade, and a 30-W cw Yb-fiber laser at 1064 nm as the fundamental source, we demonstrate SP-SHG into
the green with a conversion efficiency as high as 56% in the low as well as high-power regime, providing a 5.6 W of green output for 10 W and 13 W green output for 25.1 W of input pump power. The multi-crystal scheme permits substantial increase in cw SP-SHG efficiency compared to the conventional single-crystal scheme, without compromising performance with regard to power stability and beam quality.
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