Optical Parametric Oscillators Pumped By Raman Lasers

Optical Parametric Oscillator(OPO)is an important research direction in the field of nonlinear frequency conversion.By combining different pump sources and crystals,tunable light source in different wavelength bands can be achieved,having important application in laser lidar,laser ranging,high-resolution spectral analysis,environmental monitoring and infrared countermeasures.High-quality pump sources are very important for high-performance OPOs which are affected by pump power and beam quality.Stimulated Raman scattering(SRS)has unique properties such as pulse width compression,beam cleanup and cascade characteristics,which can obtain first-/high-order Raman light with high-power,high-beam quality without any external beam shaping device.Therefore,using a Raman laser as a pump source of OPO can not only obtain excellent OPO,but also achieve a good combination of SRS and OPO non-linear frequency conversion technology,which provides a reliable means for further expanding the laser wavelength,having a good research value.In this paper,based on the study of the cascaded Raman laser output characteristics and the beam cleanup effect,first-/second-order Nd:YVO₄/YVO₄ Raman lasers of the composite cavity are achieved considering the crystal thermal lens effect and the mode matching,and they are built as pump sources in single-resonance MgO:PPLN-OPO,respectively,and finally high-performance 1.6-1.8?m tunable lights with important application value are achieved.The specific research content is as follows:1.The SRS cleanup effect is investigated in first-and second-order compound cavity Nd:YVO₄/YVO₄ Raman lasers,respectively.At the highest 880nm LD incident power of the first-order Raman laser,the Raman light M² 1.65 is better than the fundamental light 3.08;in the second-order Raman laser,the second-order Raman light M² 1.35 is better than the first-order Raman light 1.78,better than the fundamental light 2.65,and as the incident power increases,compared with the fundamental light,Raman light can maintain a better beam quality(fundamental light M² 2.26?2.65,first-order Raman light M² 1.38?1.78,second-order Raman light M² 1.12?1.35).2.A single-resonance MgO:PPLN-OPO external-cavity pumped by 1176nm Raman laser is built,and tunable signal lights in the band of 1597?1670nm are obtained.1176nm active Q-switched Nd:YVO₄/YVO₄ Raman laser with a maximum output power of 8.05W and beam quality M² of 1.65 is achieved under a repetition frequency of 40kHz and 880nm LD pump power of 39.7W.1176nm Raman laser is used as a pump source of MgO:PPLN-OPO,the maximum Raman-signal efficiency up to 49.5% at 1638.8nm with the incident Raman power of 2W,and the highest output power of signal light is 3.2W at 1663.5nm with M² of 1.92 when the highest Raman incident power is 7.57W.3.A single-resonance MgO:PPLN-OPO external-cavity pumped by 1313nm Raman laser is built,and tunable signal lights in the band of 1778?1861nm are obtained.1313nm active Q-switched Nd:YVO₄/YVO₄ Raman laser with a maximum output power of 4.75W and beam quality M² of 1.41 is achieved under a repetition frequency of 40kHz and 880nm LD pump power of 28.1W.1313nm Raman laser is used as a pump source of MgO:PPLN-OPO,the maximum Raman-signal efficiency up to 54.8% at 1855.5nm with the incident Raman power of 1.16W,and the highest output power of signal light is 1.57W at 1855.5nm with M² of 1.87 when the highest Raman incident power is 4.0W.