Investigation of spontaneous and stimulated Raman scattering in a crystal of sodium dimolybdate, Na2Mo2O7 with an orthorhombic structure is presented. Polarized Raman spectra corresponding to six independent components of the Raman tensor have been obtained. The phonon frequencies were determined and the oscillations were identified by types of symmetry. Raman-laser mode in Na2Mo2O7 has the highest frequency value among the molybdate crystals, equal to 939 cm–1. For the first time, Raman oscillation was obtained on a Na2Mo2O7 crystal when excited by pulses of Nd:YLF laser with a wavelength of 1047 nm and a duration of 25 ps. The Raman gain coefficient at optimal orientation was 12.4 cm/GW, which is one of the highest values for solid-state Raman media. The described studies have shown that the sodium dimolybdate crystal is a promising nonlinear medium for creating a solid-state Raman converter.

The structure of ZrO2–Sc2O3 powders in the composition range from 1 to 15 mol.

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.

By reacting CeF3 with XeF2 the anhydrous CeF4 was synthesized and studied by XRD, SEM, FTIR, 19F NMR spectrometry and thermogravimetry. It was found that CeF4 undergoes hydration upon keeping in air forming the crystalline hydrate with the approximate formula [CeF4•0.2H2O]*0.7H2O. Water molecules both enter the coordination sphere of cerium and form crystalline hydrates with cerium(IV) fluoride due to OH…F hydrogen bonds in the crystal lattice.

Stimulated Raman scattering was obtained in anisotropic Na 2 Mo2 O 7 crystal with frequency shift of 37 cm -1 when excited by picosecond pulses at wavelength of 1047 nm. Raman gain coefficient was measured depending on the orientation of the crystal.

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.

Two-photon absorption was investigated in Na 2 Mo 2 O 7 anisotropic crystal under irradiation with picosecond laser pulses at 523 nm. The value of the coefficient of the two-photon absorption was measured to be 6.7 and $0.13 \mathrm{~cm} / \mathrm{GW}$, depending on the orientation of the crystal.

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.

Two nonlinear processes, namely, two-photon absorption (TPA) and stimulated Raman scattering (SRS) in Na 2 W 2 O 7 crystal at a wavelength of 523.5 nm, are studied theoretically and experimentally depending on the polarization of the incident picosecond laser radiation. It was found that, due to the anisotropy of the band gap structure, the TPA coefficient at 523.5 nm strongly depends on the pump radiation polarization. For radiation along the c axis with polarization parallel to the a axis, the TPA coefficient was measured to be 1.28 cm GW −1 , and no SRS process was registered. However, for polarization parallel to the b axis, no measurable TPA was detected and SRS with a gain of 6.5 cm GW −1 was observed. To the best of our knowledge, this is the first demonstration of the competition of two nonlinear processes in one crystal depending on its orientation.

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.

Comparative characteristics of spontaneous and stimulated Raman scattering in Pb(MoO4)1−x(WO4)x single crystals (x = 0, 0.5, 0.8, and 1.0) including both the high (ν1) and low (ν2) frequency internal anionic group vibrations have been investigated. It was found that among these crystals, Pb(MoO4)0.2(WO4)0.8 is the most suitable for multi-wavelength Raman laser in several Raman modes simultaneously. This is caused by the optimal relative Mo/W content corresponding to the most efficient coherent combination of the (MoO4)2− and (WO4)2− vibrations enhancing the output radiation characteristics of the synchronously pumped Pb(MoO4)0.2(WO4)0.8 Raman laser. Oscillation of up to twelve, closely spaced SRS components in a range of 1128–1360 nm and the strongest pulse shortening down to 1.16 ps in comparison with not only PbMoO4 and PbWO4 but also with all the earlier investigated nominally pure scheelite-like tungstate and molybdate crystals has been achieved.

The (Ca1-xSrx)(3)(VO4)(2) crystals were successfully grown by Czochralski method. Sr-3(VO4)(2) content in the CVO/SVO solid solution was varied from 10 to 45%, which corresponds to chemical compositions of (Ca1-xSrx)(3)(VO4)(2), 0.1 <= x <= 0.45. To obtain crystals of optical quality, bulk crystallization rate was decreased from 0.8 to 0.3 cm(3)/h for the nominally pure Ca-3(VO4)(2) crystal and Ca1.8Sr1.2(VO4)(2) solid solution, respectively. The Ca2.7Sr0.3(VO4)(2), Ca2.4Sr0.6(VO4)(2), Ca2.1Sr0.9(VO4)(2), Ca1.8Sr1.2(VO4)(2), Ca1.65Sr1.35(VO4)(2) and Ca1.5Sr1.5(VO4)(2) polycrystalline solid solutions were prepared by solid-state synthesis. X-ray diffraction analysis and spontaneous Raman spectroscopy were used for investigation powdered polycrystalline material and grinded single crystals. It was estimated that mono-phase solid solutions with a gradually changing structure parameters are formed in the series (Ca1-xSrx)(3)(VO4)(2) with x = 0.10, 0.20, 0.30, 0.40, 0.45. Further increasing Sr-3(VO4)(2) content in the CVO/SVO solid solution leads to formation of two-phase system. The influence of the chemical composition on the shape and size of ferroelectric domains for as-grown crystalline materials was shown.

In this Letter, a mixed Pb(MoO4)0.2(WO4)0.8 as a new, to the best of our knowledge, active medium with optimized content for a synchronously pumped multiwavelength Raman laser with a combined frequency shift is presented. The unique structure of this crystal resulted in oscillations at 12 closely spaced output wavelengths in a spectral range from 1128 to 1360 nm. The strongest pulse shortening in comparison with nominally pure scheelite-like crystals has been achieved.

Multiwavelength, near-IR (1000-1400 nm), high-repetition-rate, ultrashort laser pulses converted by cascaded stimulated Raman scattering (SRS) have many potential applications connected with multiphoton interactions of coherent radiation with matter. Utilization of mixed Raman-active crystals can make it possible not only to enrich the generated SRS radiation spectra, but also to improve other the radiation characteristics, in particular, to ensure shortening of the laser pulses. One of the candidates is a Pb(MoO 4 ) x (WO 4 ) 1 – x mixed crystal having two-mode behaviour (corresponding to the molybdate and tungstate anionic groups) for the high-frequency (ν 1 ) stretching vibrations of the anionic groups, but one-mode behaviour for the low-frequency (ν 2 ) bending vibrations of the anionic groups [1] as it shows Fig. 1 (a) for Pb(MoO 4 ) 0.5 (WO 4 ) 0.5 . Single-pass picosecond SRS in Pb(MoO 4 ) 0.5 (WO 4 ) 0.5 has been earlier realized and shown laser frequency conversion only on the two-mode ν 1 (MoO 4 ) and ν 1 (WO 4 ) stretching vibrations [2] . In the present work we demonstrate the synchronously pumped Pb(MoO 4 ) 0.5 (WO 4 ) 0.5 Raman laser operation with combined frequency shifts not only on the two-mode stretching (ν 1 ) Raman frequencies, but also on the one-mode bending ν 2 (MoO 4 + WO 4 ) broadened (Δν 2 = 10 cm –1 ) Raman line, allowing to shorten the (ν 1 + ν 2 )-shifted SRS pulses down to 1/(π c Δν ) ≈ 2 1 ps.

An all-solid-state extracavity synchronously pumped Ca3(VO4)2 Raman laser on broadened stretching (854 cm−1) and bending (354 cm−1) Raman modes with efficient stimulated Raman scattering (SRS) conversion at single frequency shift and the strongest 30-times pulse shortening down to 1.2 ps at combined frequency shift is demonstrated. The antireflection-coated, 78 mm long, a-cut Ca3(VO4)2 crystal was used as an active element under synchronous pumping by the 330 nJ, 1063 nm, 36 ps, 150 MHz mode-locked Nd:GdVO4 laser. SRS oscillation with slope efficiency of 34.2% and conversion of 18.5% at the wavelength of 1169 nm of the 854 cm−1-shifted first Stokes component with the pulse duration of 31 ps and output energy of up to 61 nJ in the external ring cavity with the output coupler reflectivity of 87% has been obtained. In the case of the second setup with high cavity Q-factor for the wavelength of 1169 nm, the additional cascade SRS component at 1222 nm with combined (854 cm−1 + 354 cm−1) frequency shift was observed. This component was generated with the slope efficiency of 8.1% and the output energy of 14.2 nJ with the output coupler reflectivity of 95%. Due to dynamics of SRS build-up in synchronously pumped extracavity Raman laser, the strongest pulse shortening at 1222 nm was achieved. The shortest pulse duration of 1.27 ps was measured at the cavity length detuning of +50 µm.