| Stimulated Raman Scattering Effect (SRSE) is a kind of nonlinear optical effect of great importance. These years, based on this effect, man can obtain great outputting ranges of waves, from the band of ultraviolet to that of near-infrared; especially for the yellow, orange and eye-safe Solid-state Raman Laser (SSRL), which is of great significance in the fields of radar measurement, medical, remote sensing and ocean exploration. So, SSRLs are drawing on increasingly much focus these years. And the research towards certain Raman Laser Crystals (RLCs), which are suitable and easy to make excellent-performance SSRLs with the feathers of small size, high reliability and high gain, is becoming a new hot point of this field.Pure molybdate and tungstate and their doped crystals are good Raman laser materials.In the most recent literatures concerning tungstate and molybdate, BaWO4, SrWO4 and BaMoO4 have been confirmed to be Raman materials with stable and effective Raman gain, and whether for picosecond pulse or as to the nanosecond pulse pump lasers, they have relatively higher Raman gain. Compared with the BaWO4, SrWO4 crystal, when used as Raman crystals has more stable Raman output energy, and is more suitable for high-energy X-ray system, because of its higher thermal conductivity and low thermal expansion anisotropy.Within the molybdates, BaMoO4, with scheelite structure, is a kind of good self-activation Raman laser material with high-peak Raman scattering cross-section. Compared with other scheelite crystals (those up to 6 cm-1), BaMoO4 is with narrower uniform width (in the 300 K 2.2 cm-1) in terms of Raman mode. Replacing Ba by Sr in BaMoO4, SrMoO4 can be obtained. SrMoO4 is with similar scheelite structure. The optical properties and X-ray effect of Er3+, Tm3+, Ho3+ adopted SrMoO4 are reported in recent literatures. Basiev and Ma et.al have confirmed that these materials are of very good Raman gain coefficiency, and are very suitable to be used as Raman materials. However, the growth of single crystal SrMoO4, especially the large-sized and high-quality crystal growth and fundamental properties are rarely reported. In this thesis, the growth, structure, defects, and the basic properties of SrMoO4 are systematically explored and researched; moreover, deep research towards the Raman lasers output of SrMoO4 single crystal has been detailed. In this study, the main work and findings are as follows:I Crystal GrowthPolycrystalline material of SrMoO4 was synthesized by solid phase reaction with the highly puritied SrCO3 and MoO3. According to the law of crystal growth, the crystal growth conditions for SrMoO4 have been discussed and studied. The temperature field for the mentioned growth processes and the growth skills were adjusted to explore large dimension and high quality crystal growth conditions. SrMoO4 crustal with high optical quality, large size is grown using Czochralski method along the a-axis and c-axis.ⅡResearch on the Structure and Defects of SrMoO4A. According to the X-Ray diffraction (XRD) images of the crystal growth powder and SrMoO4 PDF card, both the a-axised-growned and c-axised-growned single crystal are SrMoO4. The normalization of the diffraction peak shows that all the diffraction peaks belong to tetragonal system, with the space group of 141/a. Its lattice constants were calculated with the diffraction peak data as follows:a=b=5.401 A, c=12.040A, which are of a very high correspondence with JCPDS of SrMoO4.B. The crystal quality and defects detection have been done by using both chemical etching method and high resolution X-ray diffraction method. The results of SXD detection shows that the SrMoO4 grown is of good uniformity and the main defects in the crystal grown are caused by dislocation. Using HNO3 of 8mol/L as corrosive, we double-sided polished SrMoO4 chip of 4×4×2cm for corrosion. The result shows that:the main defects in the crystal grown are caused by grain boundaries and inclusions. As for the sample chip is taken from the shoulder of the crystal, so it is reasonable to believe that the crystal shoulder is a region with high dislocation density. Based on these experiments and the correspondent results, the causes account for the defects were also discussed with the aim to find a common condition for the growth of high-quality crystals.Ⅲ. Fundamental physical Properties of the As-Grown CrystalThe density and the data of thermal properties of SrMoO4 crystal were measured. The thermal properties include the thermal expansion, thermal diffusivity, specific heat and thermal conductivity.A. The density of the crystal was measured by buoyancy method, and the average density of the crystal is 4.668g/cm3.B. The crystal thermal expansion of SrMoO4 was tested using thermal mechanical analyzer (TMA). The results showed that along the a- and c- axis the thermal expansion coefficiency increases with the up-going of the temperature linearly; More precisely, the a-axis-along thermal expansion rate is much smaller than that of c-directioned, and the difference is becoming even bigger with the temperature increasing.C. The specific heat of SrMoO4 was measured with a high temperature differential thermal-DTA Used instrument (NETZSCH STA 449C) between 25℃and 300℃. And the results showed that the relationship between the specific heat and temperature is almost linear. More specifically, at 25℃the specific heat of the crystal is 0.41 Jg-1K-1; while at 300℃it is 0.69Jg-1K-1.D. The thermal diffusion of SrMoO4 was measured by the method of laser pusle. The results illustrated that the thermal diffusion along a-axis is different from that along c-axis under different temperature. For instance, at 300K,λ11=1.27mm2/sλ33=1.28mm2/s; while at 560K,λ11=0.85mm2/s andλ33=0.81mm2/s. We also found that even under the same temperature, the thermal diffusion of SrMoO4 along different directions are different, but there is one thing for sure that is, the thermal diffusion along the a-axis is always bigger than that of c-axis-directioned. Based on the data measured (the specific heat, density, thermal diffusivity and so on), the thermal conductivity of SrMoO4 was calculated. And we found the thermal conductivity along the a-axis is always higher than that of c-axised; besides, within the temperature range of 303K-550K there is little change in terms of thermal conductivity.E. The transmission spectrum of the SrMoO4 was measured by IR-Vis-UV spectrophoto-meter (Hitachi U-3500) at room temperature. The wavelength range is 305-3000nm, covering the ultraviolet, visible and near infrared and other bands; and the transmission ratio is as high as 80 percent.IV. Research on Stimulated Raman Scattering Effect of SrMoO4 and the Laser OutputThe Stimulated Raman spectra of SrMoO4 crystal was measured using Jobin-Yvon Model T64000 Raman Spectrophotometer at room temperature, and the Laser incident slit width 100μm, power 30mW, the laser wavelength 532nm, the wave number range 50-1250cm-1. The Raman peaks were identified.Up to the date, we firstly demonstrate a LD-diode-pumped Nd:GdVO4/SrMoO4 crystalline Raman laser. First Stokes laser output at 1173.5nm of 2.18W was achieved with a diode-to-first Stokes efficiency of 8.7%. With intracavity frequency doubling in LiB3O5,3.1W of cw yellow emission at 586.8nm was obtained with a 12.4% diode-to-yellow efficiency. The experimental results show that SrMoO4 is an excellent stimulated Raman scattering gain material for high-power cw near-IR Stokes and yellow lasers. |
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