Self-injection locking is a dynamic process that passively stabilizes the emission frequency of a laser through resonant optical feedback. In the conventional approach, the laser is self-injection locked to a high-Q microresonator via front facet coupling. However, the front facet power of such lasers is limited by nonlinear effects in the microresonator. In this study, we propose an alternative self-injection locking scheme using a back facet-coupled laser, where the power from the back facet is optimally tuned to avoid nonlinear effects in the microresonator. We develop a model for the proposed scheme and find the optimal states of the scheme.
A full start-to-end software (S2E) model of a laser system– including a mode-locked oscillator,
chirped pulse amplification shaper, and nonlinear upconversion– can help expand high power laser system designs routinely tackled with human-centered methodologies. S2E models can even enable reverse engineering of a laser system, allow for more streamlined exploration of parameter spaces for experimental setups, or train machine learning models for optimization and tuning of these systems. We present a generalized S2E model targeted at generating data of the photoinjector laser system at SLAC’s LCLS-II for training neural networks for optimization and, eventually, active tuning of the photoinjector.
Using a 4.5-W average power Cr2+:ZnS laser having a pulse width 43 fs and a spectral bandwidth of 138 nm centred at 2360 nm with a repetition rate of 80 MHz, we have produced femtosecond pulses in yellow wavelength. Using a 1 mm long Type 0 MgO: PPLN crystal in the first stage of our experiment, we have generated a maximum of ~ 2.43 W power of ~ 60 fs pulse width and ~ 39 nm spectral bandwidth centred at 1180 nm with a maximum conversion efficiency as high as ~ 65%. In the second stage, two different crystals, MgO:PPLN and BIBO were used to generate ultrafast coherent yellow source. The 1.18 μm radiation is first frequency-doubled in a multigrating 1 mm long Type 0 MgO:PPLN crystal with grating periods Λ=8.9 - 9.45 μm. A coherent yellow source with wavelength tunability from 577- 589 nm with a spectral bandwidth of ∼ 2 nm and temporal pulsewidth of ∼ 913 fs was achieved. At optimum focussing, we obtained a maximum power of 0.92 W for 2.2 W of pump power having a conversion efficiency of 40%. In order to address the large GVM between 1180 nm and 590 nm wavelength, we used another 1.2 mm long nonlinear crystal BIBO for birefringent phase matching. With BIBO crystal, the near-IR radiation was efficiently frequency doubled into yellow range (~ 591 nm) with average power of ~ 1 W and having a maximum conversion efficiency as high as 47%. The generated beam has a pulse width of ~ 130 fs in Gaussian shaped and ~ 4 nm spectral bandwidth with a time-bandwidth product of 0.45 showing almost no chirp. The output beam is a Gaussian shaped transverse beam profile with measured M2 values of M2x ∼ 1.07 and M2y ∼1.01.
Nonlinear frequency conversion processes depend on the polarization state of interacting beams. On the other hand, vector-vortex beams have space-variant polarization in beam transverse plane. In light of these two points, it is challenging to do nonlinear frequency conversion of vector vortex beam in single-pass geometry and retain the polarization characteristics of the beam. Here, we report an experimental scheme for single-pass second harmonic generation (SHG) of vector-vortex beams. Using two contiguous bismuth borate crystals with optic axis orthogonal to each other, we have frequency-doubled the near-IR vector-vortex beam into visible vector-vortex beams with order as high as lsh=24.
We report on efficient, two stage single-pass second harmonic generation of ultrafast Cr2+:ZnS laser with spectral bandwidth of 138 nm centered at ~2360 nm and pulse width of ~43 fs at a repetition rate of 80 MHz into tunable yellow radiation across 577 - 589 nm in multi-grating MgO:PPLN crystals. A maximum average output power ~940 mW at 589 nm wavelength with a single-pass conversion efficiency as high as 41% was achieved. The yellow radiation has a spectral bandwidth of 2 nm and pulse-width of ~913 fs in absence of any pulse compression with a time-bandwidth product of 1.58.
Laser applications of nonlinear optical (NLO) crystals are limited by their laser damage threshold. We report a detailed study of the laser damage threshold of an NLO crystal glucuronic acid γ-lactone. Second-harmonic generation efficiency of glucuronic acid γ-lactone was estimated to be 3.5 times that of standard potassium dihydrogen phosphate. Conic sections due to spontaneous noncollinear phase matching were observed. Surface laser damage studies carried out for 1064-nm radiation on a (010) plate of the crystal yielded high-threshold values of 77.72±0.27 and 32.72±0.41 GW/cm2 for single- and multiple-shot damages, respectively. The possible mechanisms for the laser-induced damage are discussed.
Bulk, transparent organic nonlinear optical (NLO) single-crystals of imidazolium L-Ascorbate (ImLA) were grown using slow-evaporation. Crystal structure was determined by single crystal X-ray diffraction analysis. Preliminary linear optical measurements through UV-Visible and infrared spectroscopy revealed good optical transmittance and a low near-UV cutoff wavelength at 256 nm. Kurtz and Perry powder test revealed that ImLA is a phase-matchable NLO material with a second harmonic generation (SHG) efficiency of 1.2 times larger than that of standard KH2PO4 (KDP). Laser damage thresholds were determined for ImLA.
Single crystals of Guanidinium L-Ascorbate (GuLA) were grown and crystal structure was determined by direct methods. GuLA crystallizes in orthorhombic, non-centrosymmetric space group P212121. The UV-cutoff was determined as 325 nm. The morphology was generated and the interplanar angles estimated and compared with experimental values. Second harmonic generation conversion efficiency was measured and compared with other salts of L-Ascorbic acid. Surface laser damage threshold was calculated as 11.3GW/cm2 for a single shot of laser of 1064 nm wavelength.
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