For the first time to our knowledge, a single-phase solid solution Sr(MoO_4) 0.8 (WO_4) 0.2 was used as an active medium of a Raman laser. Using the high-intensity synchronous picosecond pumping satisfying the condition of phase capture of the parametric Raman interaction on the second vibrational mode made it possible to oscillate six components of Raman radiation with a combined frequency shift on the first (888 cm -1 ) and second (327 cm -1 ) vibrational modes in the wavelength range of 1194-1396 nm. Oscillation efficiency of the multiwavelength Raman laser radiation was as high as 10%. By detuning the Raman laser cavity length, the pulse shortening down to 6 ps for the Raman laser radiation components with the combined frequency shift was obtained, which is an order of magnitude shorter than the pumping pulse duration (64 ps). Keywords: stimulated Raman scattering, single-phase solid solution, vibrational mode, synchronous pumping.

Highly transient stimulated Raman scattering in a SrMoO 4 crystal on both stretching (888cm - 1 ) and bending (327cm - 1 ) Raman modes under ultrafast double-pulse pumping by orthogonally polarized pump pulses at 1030 nm with a controllable chirp and a different delay between them was investigated.

Graphene-mode-locked solid-state lasers usually have a low optical efficiency (<10%) or a low output average power (<1W) due to losses in the graphene saturable absorber and the thermal load of the laser crystal. We demonstrate what we believe to our knowledge is an improved design for a highly efficient, powerful, diode-end-pumped Nd:YAG laser mode-locked with graphene. Internal losses of the laser cavity were minimized by using a high-quality monolayer graphene saturable absorber applied directly on the cavity end mirror. In comparison to other graphene-mode-locked solid-state lasers, the record high optical-to-optical and slope efficiencies of 19.1 and 24.5%, respectively, in a continuous wave mode-locking regime were achieved. The highest output average power was as high as 1.7 W for the ultrashort pulse repetition rate of 82 MHz at the beam quality of M 2 =1.3×1.4.

For the first time to our knowledge, multiwavelength, highly transient, single-pass stimulated Raman scattering with a low wavelength spacing on dual (stretching and bending) Raman modes in Sr(MoO4)0.8(WO4)0.2 and Sr(MoO4)0.4(WO4)0.6 solid solutions in a range of 1000-1300 nm (transparence window of biological tissue) under ultrafast chirped pulse laser pumping is comparatively investigated in the interests of multicolor two-photon imaging of a living tissue. For both the solid solutions, the optimum range (1-5 ps) of chirped pump pulse durations for multiwavelength Raman conversion on dual Raman modes was wider than for SrMoO4 (2-3 ps) due to the higher integral cross section of the bending Raman mode. Higher efficient SRS conversion took place at negative chirping of the pump pulse with its stretching from 0.25 ps up to 5 ps due to the compensation of a positive chirp caused by nonlinear phase modulation with total Raman conversion efficiency of up to 36 degrees lc for Sr(MoO4)0.8(WO4)0.2 and 49 degrees lc for Sr(MoO4)0.4(WO4)0.6. The highest number (five) of Stokes components in the desired range (1000-1300 nm) was observed in the optimum Sr(MoO4)0.4(WO4)0.6 solid solution, which has the Raman modes with comparable intensities. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

For the first time, to the best of our knowledge, we demonstrate highly transient, multiwavelength, single-pass Raman generation with combined frequency shifts on two Raman modes of an SrMoO4 crystal with high total Raman conversion efficiency of up to 48% in conditions of competition with self-phase modulation (SPM). A 58-mm-long SrMoO4 crystal was used as the active medium under pumping by the 1030-nm, 40-µJ laser pulses with controllable dispersive stretching in a range of 0.25-6 ps at negative and positive chirping. The pump pulse chirping was optimized for both high- and low-frequency Raman shifts on the primary (888 cm-1) and secondary (327 cm-1) Raman modes of the crystal. At the optimal conditions, four Stokes components of stimulated Raman scattering (SRS) radiation with high- and low-frequency Raman shifts at the wavelengths of 1066, 1134, 1177, and 1261 nm were efficiently generated.

For the first time to our knowledge, a single-phase solid solution Sr(MoO4)0.8(WO4)0.2 was used as an active medium of a Raman laser. Using the high-intensity synchronous picosecond pumping satisfying the condition of phase capture of the parametric Raman interaction on the second vibrational mode made it possible to oscillate six components of Raman radiation with a combined frequency shift on the first (888 cm–1) and second (327 cm–1) vibrational modes in the wavelength range of 1194-1396 nm. Oscillation efficiency of the multiwavelength Raman laser radiation was as high as 10%. By detuning the Raman laser cavity length, the pulse shortening down to 6 ps for the Raman laser radiation components with the combined frequency shift was obtained, which is an order of magnitude shorter than the pumping pulse duration (64 ps).

The effect of the self-separation of a single ultrashort light pulse of a parametric Raman CaMoO4 laser with birefringence phase matching under intracavity synchronous pumping by a mode-locked 1064 nm Nd:YAG laser is experimentally investigated and theoretically simulated. The conditions for the self-separation effect for the single ultrashort pulse at an anti-Stokes wavelength of 973 nm with the pulse duration of 9 ps and the pulse energy of up to 9 μJ are defined.

The generation of a crystalline anti-Stokes parametric Raman laser with collinear phase matching under intracavity synchronous pumping by a 1064-nm passively Q-switched longitudinally mode-locked YAG:Nd3+ laser has been studied. A CaMoO4 crystal is chosen as an active medium. This crystal has optimal birefringence for matching Stokes–anti-Stokes parametric Raman four-wave interaction at a phase-matching angle of 71° and an angular phase-matching width of 4°, which is insensitive to angular phase mismatch. The conditions for generating a single ultrashort anti-Stokes pulse at a wavelength of 973 nm with a duration of 9 ps and energy of up to 9 μJ are determined.

Theoretical and experimental studies were conducted on providing conditions for the generation of multiple radiation components with a small wavelength spacing in a crystalline synchronously pumped SRS laser with combined frequency shift on high-frequency and low-frequency vibrational modes of an SRS-active crystal. A theoretical analysis has shown an important role of four-wave parametric Raman interactions on the low-frequency vibrational mode of the crystal provided the conditions of coherence and of nonlinear phase capture of such interactions are satisfied. For the first time, SRS generation was carried out at five closely spaced wavelengths of 1194, 1242, 1294, 1336, and 1396 nm in a SrMoO 4 crystal under synchronous pumping by a high intensity picosecond YAlO 3 :Nd 3+ laser at a wavelength of 1079 nm satisfying the condition of nonlinear phase capture.

Multi-Stokes ultrashort pulse shapes and their relative positions of synchronously pumped stimulated Raman scattering (SRS) on combined primary and secondary vibrational modes in a BaWO4 crystal are investigated. An original method of its simultaneous measurement with the help of a streak camera has been developed. The structure of SRS pulses at the pulse shortening effect down to the pulse duration, close to the dephasing time of the secondary Raman mode of the BaWO4 crystal, is registered and analyzed for the detuning of the Raman laser cavity length.

We propose and study the conditions of zero-dispersion phase matching for parametric Raman interactions in birefringent crystals differing by anisotropy of zero-dispersion wavelength and allowing for the spectral tuning of the zero-dispersion phase-matching condition. We choose a highly birefringent crystal of calcite having a wide zero-dispersion anisotropy range for the demonstration of new effects of laser pulse shortening in parametric Raman lasers with spectrally tunable zero-dispersion phase matching. We demonstrate the anti-Stokes (1168 nm) and multi-Stokes (1629 nm) picosecond pulse shortening and self-separation of single 80-ps ultra-short pulse from the zero-dispersion phase-matched parametric Raman lasers that are based on the calcite crystal without using any electro-optical device.

Comparative investigation of stimulated Raman scattering (SRS) characteristics in the YVO4, GdVO4, and Ca3(VO4)2 orthovanadate crystals at both low and high frequency anionic group vibrations is presented. It was found that GdVO4 is the most perspective for SRS generation on both the ν1 stretching and ν2 bending modes of internal anionic group vibrations with the strongest SRS pulse shortening under synchronous picosecond pumping. It is as a result of GdVO4‘s widest linewidth (17cm−1) of the homogeneously broadened scheelite-type component of the bending ν2 Raman line that led to the strongest SRS pulse shortening down to the dephasing time of the widest (scheelite-type) Raman mode at the secondary intracavity short-shifted SRS conversion. It allowed us to achieve SRS pulses with sub-picosecond duration under tens-of-picoseconds pumping due to the strongest 42-fold pulse shortening. Using the Ca3(VO4)2 crystal with essentially wider Raman lines (~50cm−1) did not allow us to generate SRS pulses shorter than 1 ps. It can be explained by inhomogeneous broadening of the Raman lines in Ca3(VO4)2 because of its structural disordering. Using the measured SRS pulse duration, the homogeneous broadening of the inhomogeneously broadened bending Raman line of Ca3(VO4)2 was estimated to be ~9cm−1. Among the orthovanadate crystals, the YVO4 crystal with the highest Raman gain and with homogeneously broadened Raman lines allowed us to realize the most efficient SRS lasing and SRS pulse shortening truly down to inverse half-width of the bending Raman line.

Collinear phase matching of the Stokes ↔ anti-Stokes interaction for Raman-active crystals with different birefringence was studied theoretically as well as experimentally. It was shown that collinear phase matching of the Stokes ↔ anti-Stokes interaction in low-birefringent crystals can be insensitive to angular mismatch if a phase matching angle is higher than 60°. We have developed and experimentally realized an extracavity parametric Raman anti-Stokes laser based on a low-birefringent SrWO4. Cyan 507-nm anti-Stokes conversion from green (532 nm) pump radiation of a 5-ns, 1-mJ second harmonic Nd:YAG laser has been obtained. Laser setup with a single beam excitation made it possible to use an output face of the SrWO4 crystal as an output coupler because of wide (6°) angular tolerance of collinear phase matching that resulted in an increase of slope efficiency of anti-Stokes generation higher than 3% at the anti-Stokes energy output of a 10-µJ level.

Parametric four-wave mixing of frequency components in a crystalline Raman laser allowed generation of a collimated beam of not only Stokes, but also anti-Stokes components of the Raman radiation. Recently, to widen the angular tolerance of four-wave mixing and to obtain high conversion efficiency into the anti-Stokes wave, we have developed new schemes of the parametric Raman anti-Stokes lasers at 503 nm and 954 nm with tangentially phase-matched collinear beam interaction of orthogonally-polarized Raman components in a CaCO3 crystal under 532 nm and 1064 nm laser pumping. Now we use not only the CaCO3 crystal, but also other Raman-active crystals with different birefringence for the tangentially phase-matched parametric Raman laser under green (532 nm) pumping. We have theoretically and experimentally studied characteristics of tangential phase matching of Stokes <-> anti-Stokes interaction for different negative and positive uniaxial crystals with high and low birefringence. We have developed and experimentally realized the extracavity parametric Raman anti-Stokes lasers based not only on highly-birefringent uniaxial negative CaCO3 (1086 cm-1, 503 nm) and positive GdVO4 (882 cm(-1), 508 nm) crystals, but also on a low-birefringent uniaxial positive SrWO4 crystal (921 cm(-1), 507 nm). Cyan anti-Stokes radiation was generated from green (532 nm), 5-ns, 1-mJ pump radiation. While high-birefringent crystals require probe-pump technique of double beam excitation, the low-birefringent crystal parametric Raman laser can be developed in the simplest system of single beam excitation. The green-to-cyan anti-Stokes conversion efficiency higher 1 % was achieved in all the laser schemes.

The extracavity parametric Raman CaCO3 anti-Stokes laser at 954 nm excited by two orthogonally polarized (pump and probe) equal frequency laser beams was proposed and investigated. Tangential phase matching conditions for the orthogonally polarized Raman components four-wave mixing in the CaCO3 crystal at stimulated Raman scattering (SRS) under 1064-nm excitation were theoretically studied and applied for a novel nanosecond parametric Raman laser allowing to increase the 954-nm anti-Stokes generation efficiency. In agreement with the theoretical modeling, using the high-Q external cavity scheme we have experimentally achieved the highest optical-to-optical (1064 nm to 954 nm) efficiency of 4% in comparison with the known crystalline parametric Raman anti-Stokes lasers. The ~3 ns anti-Stokes output pulse energy was 0.3 mJ with high beam quality factor M2 = 1.1 × 1.2.