LD Pumped 1240/1485 Nm Intracavity CVD Diamond Cascade Raman Laser

Stimulated Raman scattering(SRS)is a kind of inelastic scattering that the frequency of incident light changes after scattering,belonging to the third-order nonlinear effect,and the scattering light has the characteristics of stimulated emission light.As a frequency conversion technology which depends on the fundamental wavelength,stimulated Raman scattering can extend the fundamental wavelength to the deep ultraviolet wavelength(0.2 ?m?0.35 ?m),the near infrared wavelength(0.8?m?2.5?m)and the mid infrared wavelength(2.5 ?m?20 ?m),and improve the beam quality and brightness.For the mediums producing stimulated Raman scattering,it is generally required to have a large Raman cross-section,as well as a transmission spectrum with high transmittance to both fundamental and stimulated Raman scattering light.At present,the Raman medium can be divided into liquid Raman medium,solid Raman medium and gas Raman medium.The Raman lasers based on solid Raman mediums have the advantages of compact structure,high conversion efficiency,and are widely applied in remote sensing,medical,etc.fields.CVD diamond(Chemical Vapor Deposition-Diamond)is a very excellent solid Raman medium.Compared with the traditional solid Raman medium,CVD diamond has an extremely high thermal conductivity,a low thermal expansion coefficient,high Raman gain coefficient and wide transmission spectrum.Therefore,CVD diamond has outstanding performance in the solid Raman lasers with high power and high beam quality.The research contents of this thesis are as follows:1.Based on the basic principle of stimulated Raman scattering,introduced the generation process of Stokes and anti-Stokes phonons in stimulated Raman scattering,and introduced the concept of cascaded stimulated Raman scattering;Summarized and compared the material properties of traditional solid Raman mediums,such as Raman frequency shift,thermal conductivity,transmission bandwidth,etc;and Analyzed the structures and characteristics of common solid-state Raman lasers.2.Introduced the preparation process of single crystal diamond;Described the material characteristics of single crystal diamond,and discussed the effects of polarization direction,linewidth and wavelength of fundamental laser on Raman gain coefficient of single crystal diamond,meanwhile discussed the thermal lens effect,thermal birefringence,thermal fracture threshold and damage threshold of single crystal diamond;Reviewed the research progress of CVD diamond Raman lasers.3.Analyzed the theoretical models of the external cavity Raman laser and the intracavity Raman laser,then derived the expressions corresponding to the Raman threshold and conversion efficiency,and simulated.According to the theoretical model of the Intracavity Raman laser,we used the expressions of Raman threshold and conversion efficiency to design a Raman resonator for subsequent experiments.The Raman threshold and conversion of the resonator were estimated,which provided theoretical guidance for subsequent experiments.In the design process,factors such as the thermal effects of laser crystals in the resonator and the spot size were comprehensively considered.4.Studied the LD pumped intracavity CVD diamond cascaded Raman laser.Based on the characteristics of high power density in the intracavity Raman laser,we achieved 1240 nm first-order Stokes output with low threshold successfully.Then,by optimizing the CVD diamond's placement direction,changing the overall output transmittance of the laser system,and adjusting the repetition frequency of the fundamental laser,we didn't obtain the cascaded 1485 nm second-order Stokes.but also improved the slope efficiency of 1240 nm first-order Stokes to 16.18%with about 600 mW of output power.