| As ultra-fast laser,picosecond laser plays an important role in nonlinear optical research field.The stimulated Raman scattering effect under the picosecond laser pump produces wide spectrum band picosecond laser source.Wide-spectrum band laser devices are applied to satellite laser ranging,optical microscopy,coherent spectral detection and defense application field,etc.These fields have different requirements for laser source: On the premise of satisfying the laser spectrum coverage,the average output power of the laser light source should be improved as far as possible,and the coaxial transmission characteristics of the laser output of wide spectrum band should be improved to qualified the beam quality of the laser.At the same time,the integrality of the light source should be improved as far as possible in order to be used in some situations where the limited space dimension is required.The laser output with broad spectrum can usually be achieved through cascaded stimulated Raman scattering technique.At present,one way to generate high average power with wide spectrum laser source is to use the extra-cavity pumped cascaded stimulated Raman scattering technique.While under the condition of picosecond laser pump,the conversion efficiency of cascaded stimulated Raman scattering process is relatively low.To improve the Raman conversion efficiency of picosecond pumping stimulated Raman scattering process,generally the synchronously pumping technology is deployed.In addition,the maxim?m output power output of the stimulated Raman scattering process is limited by four-wave mixing effect,laser thermal effect and selffocusing effect.Although it is possible to improve the efficiency of Raman conversion through synchronously pumping technology,the long synchronously matched Raman cavity increases the diffraction loss and also limits integration of the light source.This article in combination with the cascading effect of stimulated Raman scattering,picosecond synchronously pumping technology,four-wave mixing technology,developed pulse-train synchronously pumping technology and produced broad spectrum,high average power,picosecond coaxial output laser source.At the same time,according to the experimental results,the paper analysed the limit factors of laser average power output and the spectral range,using the developed efficient Raman resonant cavity,the output of the spectrum coverd 532 nm to 935 nm.The research described the use of Raman scattering effect of the solid-state Raman lasers in various fields of application advantages,and compared the various types of Raman laser,both domestic and abroad in the stimulated Raman scattering effect.Two aspects of theoretical research and engineering implementation situation are introduced.From two aspects of particle nature and the volatility of light,the differences between the spontaneous Raman scattering effect and stimulated Raman scattering effect are introduced,and by using the coupling equation,the cascaded stimulated Raman scattering effect was simulated to obtain the ideal theory of pump intensity;The occurrence conditions of several processes that affect the stimulated Raman scattering effect are introduced to provide theoretical support for the subsequent stimulated Raman scattering experiments.The research described the characteristics of common Raman crystals used in the stimulated Raman scattering experiment,and we compared the typical crystals in the advantages of picosecond laser pumping conditions for subsequent stimulated Raman scattering experimen to provided better characteristic Raman crystals.For the study of pulse train pump conditions of cascade stimulated Raman scattering threshold characteristics,the experiment from two aspects of pulse number and pulse interval has been carried on in the experimental research,to select suitable pump parameters for subsequent cascaded stimulated Raman scattering experiment.The picosecond single-pass cascade stimulated Raman scattering experiment,studied under the condition of high power picosecond laser pumped Raman ring angle distribution features,are studied theoretically.The Raman ring was calculated by the theory of Raman ring angle distribution.And we analyzed the reason of the error between the experimental and theoretical caculation.On this basis,we made the design of the matching of four-wave mixing effect,and carried on the generation experiment of anti-Stokes which produced up to 5 mw first-order anti-Stokes light,and 1 mW second-order anti-Stokes light.To confine the first-order Stokes,the output power factors was analyzed.This paper described the synchronously pumping technology,and ultilised the picosecond pulse-train laser pump to realize the synchronously pumping cascaded stimulated Raman scattering process,which outputs up to 5 Stokes laser and 270 mW picosecond coaxial light source.The experiment results were analyzed through the factors influencing resonator output power and output spectrum band.By optimizing the radius of curvature of the input and output mirror and the spectral transmittance characteristics,we got the highest 2.2 W,spectral 532 nm to 935 nm.And we also achieved the ninth order Stokes light output through stimulated Raman scattering process.This is so far the highest order coaxial Stokes light output by picosecond synchronously pumped technology.At the same time,in order to improve the output of laser spectral density,the multimode stimulated Raman scattering experiment,got up to 16 lines simultaneously.And the multimode stimulated Raman scattering effect experiments were analyzed,the multimode stimulated Raman scattering effect factors of conversion efficiency were also analyzed.Finally,we observed the parasitic process under cascaded stimulated Raman scattering process.In order to prove that the crystal is doped by the rare earth ions,we tested the crystal through detection of X-ray diffraction and Raman fluorescence spectrum detection and put forward the possible singular spectrum of physical process.the high power pump conditions of picosecond cascade stimulated Raman scattering experiment of Raman crystal requirements were proposed. |
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