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.

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.

The effect of magnesium co-doping on growth conditions, crystal composition, optical and spectral properties of manganese or chromium-doped Ca3(VO4)2 (CVO) crystal was studied. The single crystals were grown by the Czochralski method. Effective segregation coefficients of manganese and chromium in the CVO matrix with magnesium co-doping were calculated. A redistribution of the absorption lines intensities was observed in the absorption spectra of CVO:Mn:Mg and CVO:Cr:Mg. Low (15 K) temperature fluorescence measurements confirmed that co-doping CVO crystal with Mg ions leads to the redistribution of Mn ions concentration in different valence states, but does not cause changes in their spectral properties. In the presence of magnesium, additional annealing of the materials resulted in a slower reduction of the valence state of doping ions and a noticeable change in crystal coloration. All investigated impurities have practically no effect on the specific ferroelectric domain structure of CVO.

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.

The spectroscopic properties of cobalt ions in Ca 3 (VO 4 ) 2 crystals doped via thermal diffusion and during synthesis are investigated. The diffusion doped crystal shows the potential for higher cobalt doping while maintaining its high initial optical quality. The redistribution of several absorption and fluorescence lines intensities with cobalt concentration is attributed to the formation of Co 2+ optical centers with sufficiently different local environments. The fluorescence decay times of Co 2+ optical centers are measured to differ by an order of magnitude (95 and 13 μs) and are attributed to centrosymmetric M1 and low symmetry M2 types of Co 2+ optical centers, possibly corresponding to Ca(4) and Ca(1) positions of Ca 3 (VO 4 ) 2 crystal, respectively. Nonlinear transmission of Co 2+ M2 centers is measured, and efficient absorption cross‐sections of 1.4 × 10 −19 and 2.4 × 10 −19 cm 2 are evaluated at 1300 and 1500 nm, respectively. The narrow fluorescence line of cobalt ions peaking at about 1170 nm, detected in both Ca 3 (VO 4 ) 2 crystals doped via thermal diffusion and during synthesis, is attributed to Co ions in a trivalent state.

The simple mid-IR laser source based on femtosecond Ti:Sapphire laser and successive frequency conversion of its stretched up to 50 ps pulses in SrMoO4 Raman-active crystal and LiGaS2 second order nonlinear crystal is demonstrated. Energy of the mid-IR pulse at 11.4 mu m wavelength was up to 250 nJ that was four times higher than the previous results for the similar setup. The influence of pump pulse intensity on spectral and energetic parameters of laser pulses after SrMoO4 and LiGaS2 crystals were studied in details.

High-temperature diffusion doping has been used for the introduction of active cobalt ions in calcium orthovanadate Ca3(VO4)2 single crystals (CVO). The test samples have been produced from nominally pure Cz CVO single crystals. High-temperature diffusion conditions have been optimized for the obtaining of doped optical quality single crystals in open or closed zone annealing. The diffusion coefficients of cobalt ions have been calculated for different conditions. Temperature regime, process time, diffusant type were defined. The samples have been annealed at 1150–1300 °C for 24–48 h with Co3O4, Ca10Co0.5(VO4)7 and Ca3(VO4)2 : 2 wt.% Co3O4 as diffusants. The diffusion direction has been parallel or perpendicular to the optical axis of the CVO crystal. The diffusion coefficients have been calculated to be in the range of 2.09 · 10-8 – 1.58 · 10-7 cm2/s. The diffusion activation energies have been determined to be 2.58 ± 0.5 and 2.63 ± 0.5 eV for the [001] and [100] directions, respectively. The maximum cobalt concentration in the doped CVO crystals has been found to be 2 · 1020 cm-3. The absorption spectrum of the diffusion doped Ca3(VO4)2 : Co samples has exhibited absorption bands typical of the Co2+ and Co3+ ions. It has been shown that the intensity ratio between the characteristic absorption bands varies depending on crystal obtaining technique. The optical anisotropy of the crystal increases with dopant concentration.

The spectroscopic properties of cobalt ions in Ca 3 (VO 4 ) 2 crystals doped via thermal diffusion and during Czochralski growth process are studied. The spectroscopic properties of M1 and M2 Co 2+ optical centers are presented. A narrow fluorescence line at 1170 nm is attributed to trivalent Coions.

New high optical quality calcium orthovanadate Ca-3(VO4) (2) crystal doped by chromium ions was synthesized. Polyvalent character of doping chromium ions in as-grown crystal was revealed. Crystal annealing at 1000 degrees C seems to result in increase of chromium ions in four plus state. Spectroscopic properties of chromium ions in Ca-3(VO4)(2) crystal were investigated.

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).

Activation of calcium orthovanadate crystals by cobalt ions was carried out by introducing cobalt oxide into the melt during Czochralski growth process or during high-temperature annealing of nominally pure Ca3(VO4)2 single-crystal using Co3O4 powder as a solid-phase diffusant. The maximum concentration of the Co ions in the matrix is achieved in the case of the diffusion doping process. For the concentration series of Ca3(VO4)2:nCo crystals, the local structure was investigated and the crystal chemical composition was determined. Polarized absorption spectra of doped crystals are obtained. The influence of the atmosphere and the annealing temper-ature on the redistribution of the intensities of the characteristic absorption bands in the visible and near-IR spectral regions is shown. Luminescence parameters of the doped crystals were studied.

The effect of focusing, taking into account self-focusing, on the interference of SRS (stimulated Raman scattering) and self-phase modulation in a 8-mm BaWO4 crystal pumped by laser pulses with a duration of 0.3 ps and a wavelength of 515 nm is experimentally studied. The maximum efficiency of SRS conversion (~23%) to the Stokes component of the ν1 = 925 cm–1 strongest mode is obtained with a lens with a focal length of 40 mm at the linear focus shift towards the rear facet of the crystal. The increase in efficiency, when the linear focus is shifted to the rear facet, is associated with an increase in the distance between the linear and nonlinear foci, which results in an increase in the effective length of the nonlinear interaction.

Transient stimulated Raman scattering (SRS) of chirped, temporally stretched up to 45 ps, Ti:sapphire laser pulses was studied in three different Raman-active crystals (BaWO4, SrMoO4 and Ca-3(VO4)(2)) at the same experimental conditions. BaWO4 and SrMoO4 crystals had the same SRS ''threshold'' energy/intensity, which was associated with their similar integrated cross sections for spontaneous Raman scattering. The highest energy SRS efficiency was obtained in SrMoO4 crystal and reached 8%, which was two-times higher than one in BaWO4. Higher SRS efficiency in SrMoO4 was observed due to lower nonlinear absorption. The Ca-3(VO4)(2) crystal had significantly higher SRS ''threshold'' and lower efficiency despite the lowest nonlinear absorption losses. A simple expression of exponential gain for transient SRS of chirped laser pulses was proposed and verified by comparison with experimental results. This expression was used to estimate dephasing time T-2 of Ca-3(VO4)(2) crystal which was 8.5 +/- 1.0 ps.

The prospects of SRS-active calcium/strontium orthovanadate crystals, Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2, for spectral conversion of ultrashort visible-range laser pulses evaluated in a single-pass scheme with pump focusing into the samples. For the ~3 J incident laser pulses of 0.3 ps duration at wavelength of 515 nm the energy conversion efficiency of up to ~3.5% to the Stokes component shifted in frequency by ~850 cm–1 obtained in a 1.3 cm long sample of Ca2.7Sr0.3(VO4)2 crystal. Simultaneously, in the transmitted radiation spectrum the amplitude of Stokes component reached 1/3 of the amplitude at the pump wavelength. Under the same conditions, SRS in a Ca3(VO4)2 crystal was not detected at all. It was shown that the observed differences can be explained by the attenuation of pump pulse due to difference in two-photon absorption in these crystals.

Two-photon absorption has been systematically studied in Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2 crystals, both of which are prospective nonlinear optical and laser host materials. A strong dependence of the two-photon absorption coefficients on the orientation of the laser beam polarization with respect to the optical c-axis of the crystals is revealed. The measured coefficients for perpendicular and parallel orientations were 50 ± 10 cm/TW and 19 ± 4 cm/TW in Ca3(VO4)2, and 18 ± 3 cm/TW and 10 ± 2 cm/TW in Ca2.7Sr0.3(VO4)2, respectively. Thus, to minimize optical losses caused by two-photon absorption, an orientation of Ca2.7Sr0.3(VO4)2 crystals with the laser beam polarization parallel to the crystal optical c-axis is preferred.

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.

In this work, the high-temperature diffusion doping method was used for introduction of active cobalt ions into calcium orthovanadate Ca3(VO4)2crystals. Experimental samples were made from a nominally pure CVO single crystal obtained by the Czochralski method. The high-temperature diffusion conditions have been optimized to obtain doped crystals of optical quality during annealing in open and closed zones. Diffusion coefficients of cobalt ions (D) were calculated for various conditions: annealing time 24 - 48 hours; temperature range 1150-1300°C; diffusants - oxide compounds of calcium, cobalt and vanadium: Co3O4, Ca10Co0.5(VO4)7 and Ca3(VO4)2:2wt.%Co3O4; diffusion direction is parallel or perpendicular to the CVO crystal optical axis. The calculated values of the diffusion coefficient varied between 2.09·10-8—1.58·10-7 cm2/s. The activation energy of the diffusion process was determined to be 2.58±0.5 and 2.63±0.5 eV for the [001] and [100] directions, respectively. The maximum cobalt concentration in doped CVO crystals was 2·1020 cm–3. The absorption spectrum of diffusion-doped Ca3(VO4)2:Co samples demonstrates the presence of absorption bands characteristic for Co2+ and Co3+ ions. It was shown that the intensity ratio of the characteristic absorption bands varies depending on the crystal doping method. The optical anisotropy of the crystal increases with dopant concentration increase.

Luminescence properties of nominally pure and doped with Eu3+ and Pr3+ ions SrMoO4 single crystals grown by the Czochralski method have been studied. Thermal quenching of intrinsic emission of pure and doped SrMoO4 single crystals has been observed, as well as a correlation of thermal quenching activation energies with rare-earth ion concentration has been observed. Tunable laser was used to study time-resolved luminescence in a range from 10 K to room temperature. The effect of dopant nature and concentration on intrinsic emission and decay kinetics has been elucidated.

Stimulated Raman scattering of chirped Ti:Sapphire laser pulses in BaWO4 crystal A spectrum transformation of a chirped Ti:sapphire laser pulse stretched to 0.2 ns (with initial transform limited pulse duration of 90 fs) was experimentally studied in a tandem of BaWO4 crystals. To increase stimulated Raman scattering efficiency, broadband laser emission was used as a seed of this process. Efficiency of the Stokes component generation corresponding to the BaWO4 crystal phonon mode ν1(Ag)≈925 cm-1 reached ~ 10%. Generation of the Stokes component corresponding to the weaker phonon mode ν3(Eg)≈795 cm-1, and second Stokes components of ν1(Ag) and ν3(Eg) modes were also observed. Mechanisms reducing the stimulated Raman scattering efficiency for the ν1(Ag) mode are discussed.