Nd:YLF laser at cryogenic temperature with orthogonally polarized simultaneous emission at 1047 nm and 1053 nm

Triple-Wavelength Lasing with a Stabilized β-LaBSiO5:Nd3+ Crystal

Multi-wavelength lasers, especially the triple-wavelength laser around 1060 nm, could be produced by the ⁴F_3/2 → ⁴I_11/2 transition of Nd³⁺ and present numerous challenges and opportunities in the field of optoelectronics. The Nd³⁺-doped high-temperature phase of LaBSiO₅ (β-LBSO) is an ideal crystal to produce triple-wavelength lasers; however, the crystal growth is challenging because of the phase transition from β-LBSO to low-temperature phase (α-LBSO) at 162 °C. This phase transition is successfully suppressed when the doping content of Nd³⁺ is larger than 6.3 at. %, and the Nd³⁺-doped β-LBSO is stable at room temperature. The local disorder of BO₄ tetrahedra due to Nd³⁺ doping is essential to the stabilization of β-LBSO. For the first time, the β-LBSO:8%Nd³⁺ crystal with a dimension of 1.8 × 1.8 × 1.8 cm³ is obtained through the top-seeded solution method. The crystal shows strong optical absorption in the range of 785-815 nm, matching well with the commercial laser diode pumping source. The optical emission of ⁴F_3/2 → ⁴I_11/2 splits into four peaks with the highest optical emission cross section of 2.14 × 10^-20 cm² at 1068 nm. The continuous-wave triple-wavelength generation of coherent light at 1047, 1071, and 1092 nm is achieved with the highest output power of 235 mW and efficiency of 12.1%.

Excellent performance of a cryogenic Nd:YAlO3 laser with low wavefront distortion based on zero thermal expansion

High-power solid-state lasers with good beam quality are attracting great attention on account of their important applications in industry and military. However, the thermal effects generated in the laser host materials seriously limit power scaling and degrade the beam quality. Thermal lensing and thermally induced wavefront deformation are the main causes of the beam quality deterioration. Here we investigate the performance of a zero thermal expansion (ZTE) solid-state laser gain material. In a proof-of-principle experiment, an ${a}$-cut rod ${\rm Nd}\!:\!{{\rm YAlO}_3}$ (Nd:YAP) perovskite crystal is chosen to be the gain medium for ZTE around 180 K. The laser performance spanning the temperature range from 80 to 290 K is studied. The maximum output power and minimum threshold pump power were obtained at a temperature of 180 K. Moreover, the measured thermal focal power and peak-to-valley value of the wavefront distortion also reach a minimum at this temperature, an additional benefit from the crystal's ZTE coefficient. We envisage that these results will open a new route towards the development of high-power and high-beam-quality lasers through the use of ZTE gain materials.

High power (>500W) cryogenically cooled Yb:YLF cw-oscillator operating at 995 nm and 1019 nm using E//c axis for lasing

We present record continuous wave (cw) output power levels from cryogenically cooled Yb:YLiF₄ (Yb:YLF) lasers in rod geometry. The laser system is pumped by a state-of-the-art 960 nm diode module, and vertically polarized lasing was employed using the E//c axis of Yb:YLF. Lasing performance was investigated at different output coupling levels in different cavity configurations and the laser crystal temperature was estimated via monitoring the emission spectrum of the gain media. We have obtained a cw output power up to 400 W at a wavelength of 995 nm. The absorbed pump power was around 720 W, and the laser output had a TEM₀₀ beam profile with an M² of 1.3 in both axes. At higher absorbed pump power levels with increasing laser crystal temperature, we observed a lasing wavelength shift from 995 nm to 1019 nm. In this regime cw output power levels above 500 W have been achieved at an absorbed pump power of 750 W. Further power scaling was limited by the onset of strong thermal lensing. We discuss underlying physical mechanisms for the wavelength shift and present detailed temperature measurements under lasing conditions.

Temperature-Dependent Stimulated Emission Cross-Section in Nd3+:YLF Crystal

Spectroscopic properties of neodymium-doped yttrium lithium fluoride were measured at different temperatures from 35 K to 350 K in specimens with 1 at% Nd3+ concentration. The absorption spectrum was measured at room temperature from 400 to 900 nm. The decay dynamics of the 4F3/2 multiplet was investigated by measuring the fluorescence lifetime as a function of the sample temperature, and the radiative decay time was derived by extrapolation to 0 K. The stimulated-emission cross-sections of the transitions from the 4F3/2 to the 4I9/2, 4I11/2, and 4I13/2 levels were obtained from the fluorescence spectrum measured at different temperatures, using the Aull-Jenssen technique. The results show consistency with most results previously published at room temperature, extending them over a broader range of temperatures. A semi-empirical formula for the magnitude of the stimulated-emission cross-section as a function of temperature in the 250 K to 350 K temperature range, is presented for the most intense transitions to the 4I11/2 and 4I13/2 levels.

Generation of a simultaneous orthogonally polarized dual-wavelength Raman laser with power ratio tunability by a single hexagonal crystal: Cs2TeMo3O12

A new generation of orthogonally polarized dual-wavelength lasers was demonstrated using a dye mode-locked neodymium-doped yttrium aluminum garnet laser for the first time. With a hexagonal Cs₂TeMo₃O₁₂ as the Raman medium, efficient dual-wavelength stimulated Raman scattering was obtained at 1175 and 1154 nm with similar output power, corresponding to the stretching vibration of Mo-O and the asymmetric stretching vibrations of Mo-O and Te-O groups, respectively. The power ratio of two Raman components can be flexibly adjusted by tuning the polarization of the incident laser, which can be tuned from 0% to 100%. Laser sources with such a small wavelength separation could prove interesting for the difference-frequency generation of terahertz waves in the 4.6 THz range. Our study provides a simple and flexible method to achieve a promising dual-wavelength laser source in orthogonal polarization by Raman-based nonlinear frequency conversions.

Frequency expansion of orthogonally polarized dual-wavelength laser by cascaded stimulated Raman scattering

In this Letter, the frequency expansion of an orthogonally polarized dual-wavelength laser, based on the cascaded stimulated Raman scattering, was demonstrated for the first time, to the best of our knowledge. The dual-wavelength fundamental laser generated from two separate Nd:YLF crystals was free of gain competition. Integrating the benefit of the two different orthogonally polarized Raman gain peaks in the KGd(WO₄)₂ (KGW) crystal, two sets of first-Stokes orthogonally polarized dual-wavelength Raman lasers were first achieved by rotating the Raman crystal for 90°. Furthermore, by simply replacing the Raman output coupler, we attained another two sets of second-Stokes orthogonally polarized dual-wavelength Raman lasers via the cascaded Raman shift. At a pulse repetition frequency of 5 kHz, the maximum first-Stokes and second-Stokes dual-wavelength Raman output powers were 3.12 and 2.09 W, with the combined peak powers of approximately 240 and 290 kW, respectively.

Power scaling of an actively Q-switched orthogonally polarized dual-wavelength Nd:YLF laser at 1047 and 1053 nm

We report a high average power actively Q-switched (AQS) orthogonal polarization dual-wavelength Nd:YLF laser at 1047 and 1053 nm. The gain-to-loss balance of dual wavelengths was realized via an uncoated quartz etalon. A maximum continuous wave (CW) output power of 14.2 W was obtained under the incident pump power of 41.7 W, corresponding to an optical-to-optical conversion efficiency of 34.1% and a slope efficiency of 38.3%. Active Q-switching was accomplished by inserting an acousto-optic modulator in the cavity. Under the incident pump power of 40 W, this setup delivered a maximum average output power of 10 W at the pulse repetition frequency (PRF) of 30 kHz and the largest pulse energy of 3.4 mJ at the PRF of 1 kHz, respectively. To the best of our knowledge, these are the highest average output powers for both CW and AQS orthogonally polarized dual-wavelength lasers based on laser crystals.

Megahertz-level, high-power picosecond Nd:LuVO4 regenerative amplifier free of period doubling

We report on a high repetition rate, high-power picosecond Nd:LuVO₄ regenerative amplifier. Period doubling caused energy instability was eliminated at megahertz-level repetition rate with the modified seeding source. A multi-pass cell was used to improve the seed pulse energy to achieve complete suppression of the onset of bifurcation. At a maximum repetition rate of 1.43 MHz, the system produced 7.0-ps-long pulses with an average output power of 25.1 W, corresponding to a pulse energy of 17.6 μJ. At 100 kHz, the pulse energy increased to 205 μJ with an average power of 20.5 W. Moreover, the injected pulses with pulse duration of 5.1 ps broadened to 8.9 ps because of gain narrowing in the amplifier.

High power, high repetition rate, few picosecond Nd:LuVO₄ oscillator with cavity dumping

We investigate the potential use of Nd:LuVO4 in high average power, high repetition rate ultrafast lasers. Maximum mode-locked average power of 28 W is obtained at the repetition rate of 58 MHz. The shortest pulse duration is achieved at 4 ps without dispersion compensation. With a cavity dumping technique, the pulse energy is scaling up to 40.7 μJ at 300 kHz and 14.3 μJ at 1.5 MHz.

Efficient orthogonally polarized dual-wavelength Nd:LaMgB₅O₁₀ laser

We reported an efficient, continuous-wave, diode-pumped, orthogonally polarized dual-wavelength laser working at 1051.8 and 1081.4 nm in a new neodymium-doped borate crystal, Nd:LaMgB5O10, which was grown by the top-seeded solution growth method. A maximum output power of 5.1 W was obtained with an absorbed pump power of 14.8 W, corresponding to an optical-to-optical conversion efficiency of 34.5% and a slope efficiency of 42.5%. By slightly tilting the laser cavity output mirror, the balanced dual-wavelength emissions were obtained with the total output power as high as 4.2 W. This new efficient dual-wavelength laser may be a promising light source for terahertz generation with a rarely large frequency difference of 7.8 THz through difference frequency generation.

Two-frequency pulsed YLiF₄:Nd lasing out of the principal axes and THz generation

Thanks to a propagation direction at 50.3° from the c axis in a LiYF4:Nd crystal, we have equalized the emission cross-sections at 1047 and 1053 nm, respectively, for extraordinary and ordinary waves. The double refraction is used to balance the "o" and "e" pumping. Actively Q-switching the laser cavity leads to simultaneous pulses with duration less than 10 ns. Frequency conversion to THz radiation was performed through difference frequency mixing in two nonlinear crystals: GaSe and OH1. In the first case, we obtained 132 nW and in the second case we obtained 51 nW THz power at 6.67 kHz repetition rate.

Intracavity continuous-wave multiple stimulated-Raman-scattering emissions in a KTP crystal pumped by a Nd:YVO(4) laser

Intracavity continuous-wave (CW) multiple stimulated-Raman-scattering emissions have been successfully demonstrated in a KTP crystal pumped by a Nd:YVO(4) 1064-nm laser for the first time. Three different output couplers (OCs) with high-reflection (HR) coating in the range of 1-1.1, 1-1.13, and 1-1.15 μm are employed in the experiment to generate lasing wavelengths at 1095 (the first-Stokes emission of the 266 cm(-1) Raman shift), 1095 + 1128 (the first- and second-Stokes emission of the 266 cm(-1) Raman shift), and 1095 + 1128 + 1149 nm (the first two Stokes emissions of the 266 cm(-1) Raman shift and the first-Stokes emission of the 694 cm(-1) Raman shift), separately. This Raman laser paves a way to produce more-closely spaced set of CW emission in the green-yellow region.