Structure And Spectral And Thermal Properties Research On Nd: YbVO₄ Laser Crystal

As one of the primary materials of solid-state laser, because of crystal's properties of good optics, physics and chemistry, thermotics etc, it has become the emphasis of study and has been applied and developed. Since observed the laser output of Nd³⁺ ion in the CaWO₄ crystal in 1961, because of the properties of abundant ion energy level, matching between the absorption peak of 808nm and pumped wavelength of pumping source, high absorption and emission cross section, Nd³⁺ ion has become the active ion that was used generally. The Nd³⁺ ion was doped in different vanadate host crystals, Nd:YVO₄ crystal has become the primary material of commercial medium and small sized laser, Nd:GdVO₄ crystal was applicable for high-capacity LD pumping solid-state laser. As a new laser crystal doped Nd³⁺ ion, Nd:YbVO₄ crystal was easy to work, chemical property was stable, had good optical homogeneity and thermal property. Above all, the study on this crystal not only extend the knowledge of optical and thermal properties of vanadate crystals, but make the foundation of laser property.(1) The developing course, application, character of solid-state laser were summarized, from the character of good laser crystal, the advantage of crystal as one of materials of solid-state laser was explained. The character of lightening in crystal doped Nd³⁺ ion, advantage and disadvantage of application of many kinds of laser crystal doped Nd³⁺ ion were summarized.(2) The vibration spectrums of crystal including Raman and infrared absorption spectroscopy were introduced. The classical and quantum theory of Raman scattering were introduced particularly, compared Raman and infrared absorption spectroscopy, the characters were specific respectively, and election rules of vibration spectrum was expatiated in datail. Based on theory of factor group, the normal vibration mode of the crystal was stapled, the Raman-active vibration modes were confirmed, they are 5A_1g,7B_1g,2B_2g,10E_g respectively, and infrared-active vibration modes were 2A_2g,9E_u respectively, the Raman spectrum was measured by the micro-Raman spectrophotometer, with four different scattering geometry, the infrared absorption spectrum was measured by infrared spectrophotometer, the vibration frequency of Raman and infrared-active vibration mode were signed, the mode of vibation of VO₄^3- ion group was studyed roundly.(3) J-O theory and formula were introduced, ultraviolet-visible-near infrared absoption spectrum was measured, the full width at half maximum of absorption peak at central wavelength of 808nm is 12nm. Based on the Judd-Ofelt theory, thethree intensity parameters have been calculated and the results areΩ₂ = 6.88945×10^-20cm²,Ω₄= 4.13394×10^-20cm² andΩ₆ = 4.54503×10^-20cm². The radiativelifetime of ⁴F_3/2 is 178.69μs, branching ratio at 1062nm is 48.85%, differential stimulated -emission cross section is 2.7867×10^-18 cm². From the fluorescent spectra excited by 808nm and 940nm, the Nd→Yb and Nd←Yb energy transfer have been observed.(4) The physical meaning of material thermal expension was introduced simply, the crystal's coefficient of thermal expension of three directions were measured in theexperiment, they areα_a=2.5×10^-6／K,α_b=2.6×10^-6／K,α_c=8.7×10^-6／Krespectively. The heat capacity and specific heat of solid were expatiated, based on Dulong's law and Kopp's law, the constant volume specific heat was calculated, it is 116.8J/K·mol, that have difference comparing with constant pressure specific heat 129.46-186.99 J/K·mol. The macrography and microscopic law of thermal conductivity were listed, the coefficients of thermal conductivity were calculated by the density and specific heat, the coefficients of thermal conductivity of a and c direction become low as the temperature become high, and the c direction's is higher than a direction's.