Study On Tunable Raman Iasers Of KTiOPO₄ And KTiOAsO₄ Crystals

Nonlinear optical frequency comversion is an important way to extend the alser spectral range.Nonlinear optical effects mainly include the second-order and third-order nonlinear optical effects.The second-order nonlinear optical effects include sum frequency generation,difference frequency generation,second harmonic generation,optical parametric oscillation,etc.The third-order nonlinear effects include stimulated Raman scattering(SRS),stimulated Brillouin scattering,four-wave mixing,etc.The stimulated polariton scattering(SPS)is another form of light-matter interaction.It is an optical phenomenon that contains both the second-order and third-order nonlinear effects.SPS is often used to generate tunable terahertz waves and,at the same time,tunable near-infrared lasers.Sometimes two or more nonlinear optical effects are used together to extend the laser spectral range further.For example,stimulated Raman scattering and second harmonic generation can be used together to obtain the laser waves at the yellow and orange spectral ranges of 580-620 nm by using the pumping laser at 1064 nm.The setup is compact and the beam quality is high.KTiOPO4(KTP)and KTiOAsO4(KTA)are excellent nonlinear optical crystal materials.They have been widely studied and applied in optical parametric oscillation,frequency doubling,sum frequency generation,difference frequency generation,etc.They are also excellent Raman crystals and widely applied in solid state Raman lasers.Recently KTP and KTA crystals are found to be suitable for stimulated polariton scattering and can be used to generate terahertz wave and tunable infrared laser.In this thesis,the combination of the stimulated polariton scattering and stimulated Raman scattering is used in KTP and KTA crystals for the first time to extend the laser spectral range.The main research contents are as follows.1.The KTiOPO4 Stokes parametric oscillator is placed in the cavity of the 1064.16 nm LD-end-pumped Q-switched Nd3+:YAG laser.When the non-collinear phase matching angle between the pumping and Stokes beams changes between 2.30°-5.60°,the generated Stokes laser based on stimulated polariton scattering(SPS Stokes laser)can be tuned from 1080.13 nm to 1081.70 nm,from 1082.72 nm to 1083.80 nm,from 1085.12 nm to 1087.49 nm.This SPS Stokes laser is used as the pump source of the Raman laser in which the collinear stimulated Raman scattering is realized in the same KTiOPO4 crystal.By designing the output mirror transmittance of the Stokes cavity,the output of the first-order Raman light is selected,the laser(SRS Stokes laser or first order Raman laser)wavelength tuning range can be from 1112.08 nm to 1113.75 nm,from 1114.94 nm to 1115.85 nm,from 1117.37 nm to 1119.92 nm.The Raman laser sprctum,the dependences of the SPS and SRS Stokes wavelengths and powers on the phase matching angle are investigated in detail.When the LD pump power is 6.00 W,the phase matching angle is 4.55°,and the pulse repetition frequency is 7 kHz,the obtained maximum average output power is 734 mW,the corresponding conversion efficiency is 12.2%.2.The KTiOAsO4 Stokes parametric oscillator is placed in the cavity of the LD-side-pumped Q-switched Nd3+:YAG laser.By the combination of the stimulated polariton scattering and stimulated Raman scattering,tunable Raman laser is obtained.When the non-collinear phase matching angle between the 1064.16 nm pumping and SPS Stokes beams changes between 2.00°-6.00°,the SPS Stokes laser can be tuned from 1078.20 nm to 1078.72 nm,from 1079.20 nm to 1081.34 nm,from 1082.74 nm to 1083.72 nm,from 1085.54 nm to 1085.68 nm,from 1086.94 nm to 1088,20 nm.The corresponding first order Raman laser can be tuned from 1106.08 nm to 1107.40 nm,from 1107.52 nm to 1109.20 nm,from 1110.6 nm to 1111.90 nm,from 1113.96 nm to 1114.10 nm,from 1115.22 nm to 1116.62 nm.When the first order Raman laser wavelength is 1116.34 um,the output power is maximum.When the LD pump power is 94.20 W,the pulse repetition frequency is 5 kHz and the phase matching angle is 5.60°,the obtained maximum average output power is 1.62 W.