Structured coherent optical beams including optical vortices, hollow Gaussian beam, and Airy beam have found wide range of applications in variety of fields in science and technology. All existing techniques used to date to generate such beams suffer from different limitations including lower output power and restricted wavelength coverage. On the other hand, interactions of such beams with nonlinear media are mostly unexplored. We have been involved in the study of nonlinear interaction of optical beams with different spatial structures. Here, we discuss our recent results on nonlinear generation of various structured laser beams including optical vortices, perfect vortices, Airy beam, and hollow Gaussian beam and some of their applications
We report on development of tunable, cw, single frequency ultraviolet (UV) source based on intra-cavity frequency
doubling of an optical parametric oscillator (OPO). The singly resonant OPO (SRO) is realized using 25 mm long MgOdoped
periodically poled stoichiometric lithium tantalite (MgO:sPPLT). The SRO, pumped in the green, is intra-cavity
frequency doubled using two different crystals β-BaB2O4 (BIBO) and periodically poled KTiOPO4 (PPKTP) to generate
tunable UV radiation. The BIBO based source produces UV radiation with output power as much as 770 mW at 398.24
nm in elliptic (0.66) spatial beam while pumping at 8W of green power. The UV source can be tuned across 355.2-418
nm with a continuous wavelength tunability of 62.8 nm in single frequency radiation with instantaneous line-width of
14.5 MHz. On the other hand, the PPKTP based UV source generates maximum UV power of 336 mW at 398.28 nm and
wavelength tunability of 18.1 nm in a TEMOO spatial mode with ellipticity of 0.93 for 5W of green pump power. The
line-width of the UV radiation is measured to be 18.5 MHZ. In comparison, PPKTP based UV source provides better
performance than BIBO in terms of beam quality and power stability.
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 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.
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 TEM<sub>00</sub> 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 TEM<sub>00</sub> spatial profile with M<sup>2</sup><1.44 across the tuning range and exhibits a peak-to-peak power fluctuation below 5.1% over 1 hour.
We describe new sources of tunable, high-power radiation in the blue and ultraviolet. Continuous-wave (cw), singlefrequency
blue radiation tunable across 425-489 nm and femtosecond ultraviolet (UV) radiation tunable across 250-355
nm is generated by intracavity frequency-doubling of resonant signal radiation in cw and ultrafast optical parametric
oscillators (OPOs) in singly-resonant oscillator (SRO) configuration. The cw SRO, pumped in the green, uses a 30-mm
MgO:sPPLT as the nonlinear material and a 5-mm BiB<sub>3</sub>O<sub>6</sub> (BIBO) crystal for internal doubling. Using this approach, we
generate 1.27 W of cw blue power with a linewidth of 8.5 MHz and a TEM<sub>00</sub> profile. The device also generate a singlefrequency
signal output of ~100 mW across 850-978 nm and up to 2.6 W of idler power in the 1167-1422 nm spectral
range. The femtosecond SRO, based on a 400-μm BIBO crystal and pumped at 415 nm in the blue, can provide visible
femtosecond signal pulses across 500-710 nm. Using a 500-μm crystal of β-BaB<sub>2</sub>O<sub>4</sub> internal to the SRO cavity, efficient
frequency doubling of the signal pulses into the UV is achieved, providing tunable femtosecond pulses across 250-355
nm with up to 225 mW of average power at 76 MHz. Cross-correlation measurements result in UV pulses with durations
down to 132 fs for 180 fs blue pump pulses.