Research Of The Passively Q-switched Nd:YAP/YVO₄ Raman Laser And Its Frequency Mixing Laser

Stimulated Raman Scattering is an efficient frequency conversion approach to generate novel wavelength laser,which has many excellent properties such as requiring no phase matching,beam cleaning and the pulse width compression,which has been a gathering topic for the study of lasers and nonlinear optics.The Cr⁴⁺:YAG passive Q-switched solid-state Raman laser fully combines the advantages of solid-state laser technology,solid-state Raman medium and solid-state saturable absorber,which has the important value for developing the field application solid pulse lasers devices with miniaturized,easy adjustment,highly reliable,and economical.YVO₄ crystal has various Raman spectral characteristics whose multiple Raman spectra modes corresponding to its different polarization configurations has the great value to enrich the laser output wavelength.In this thesis,an a-cut YVO₄ crystal is used as Raman crystal,and a b-cut Nd:YAP rod crystal with superior energy storage capability is used as laser crystal.Consequently,the output characteristics of different Raman modes in YVO₄ crystal excited by the passively Q-switched 1080 nm fundamental laser has been investigated.Then,the second harmonic generation and sum frequency generation of the fundamental and Raman laser in intracavity were further studied,and the orange-yellow-green wavelength switchable emission output was obtained.Manifested as follows are the primary contents of this thesis:1.The output characteristics of the diode-end-pumped passively Q-switched Nd:YAP/YVO₄ Raman laser based on different Raman shifts were investigated.A Cr⁴⁺:YAG/YAG composite crystal was employed as the saturable absorber to support the passively Q-switched operation.When employing different transmission loss through the output mirror in the first-stokes region based on the Raman shifts of 890 and 816 cm^-1,combining with the anisotropy of the Raman spectrum in YVO₄ crystal,the corresponding first-stokes outputs under different Raman configuration were realized.By setting the polarization direction of the Nd:YAP laser corresponding to the X（YY）X Raman configuration in YVO₄,the strongest Raman shift of 890 cm^-1 was successfully suppressed,and the Raman laser outputs only include the 1183.7 nm single Raman wavelength based on the Raman shift of 816 cm^-1in YVO₄.When the polarization direction in YVO₄corresponding to the X（ZZ）X Raman configuration was further adjusted,and the single Raman wavelength of 1194.6 nm based on the Raman shift of 890 cm^-1was obtained.Under the incident pump power of 9.87 W,the maximum average output power of 850 m W and 760 m W with conversion efficiency of 8.6%and 7.7%were obtained for the wavelength of 1183.7 nm and 1194.6 nm.The corresponded pulse widths were 3.5 ns and 1.5 ns with the pulse repetition frequency of 28.4and 33.5 k Hz,respectively.According to the experimental results,the factors which affects the threshold,pulse repetition frequency and pulse width of the passive Q-switched laser based on Raman effects was thoroughly investigated.This study provides an important reference for the design of passively Q-switched Raman lasers.2.Based on the research of the passively Q-switched YVO₄ Raman laser,the nonlinear frequency mixing generation in intracavity was further designed.A BBO crystal with small phase matching angle difference between different wavelengths in the cavity is used as nonlinear optical crystal.Thus,the compact and efficient three wavelengths switchable output of orange-yellow-green laser was realized.Consequently,under the incident pump power of 12.05 W,the maximum average output power of472 m W for 597.4 nm orange light,431 m W for 567.2 nm yellow light and 803m W for 539.9 nm green light were obtained with respective pulse widths of about 2.6,2.4 and 37.6 ns.Moreover,the pulse repetition frequency and the single pulse energy of 11.6,10.9,13.4 k Hz and 40.7,39.5,59.9μJ were obtained under the maximum incident pump power,respectively.