Highly Efficient Operation Of 1.18μm All-solid-state Raman Lasers And Investigation Of The Eye-safe Raman Lasers

Stimulated Raman scattering is an attractive method of frequency conversion based on the third-order nonlinear optical process.The wavelength of the scattered light is determined by the wavelength of the pumped light and the Raman shifts of the Raman-active media.By selecting different pumping source and Raman-active media,the laser spectrum reachable with SRS can extend from the ultraviolet to the near infrared. Raman-active media include gases,liquids and solids.Compared with gases and liquids, the solid-state Raman-active media offer high gain,high molecule density,favorable thermal and mechanical properties,narrow linewidth of the vibrational modes and compatibility with the compact all solid-state laser technology.The all-solid-state Raman lasers take advantages of compactness,high efficiency and high stability,which make it feasible for their wide applications in such fields as information,communication,medical treatment,measurement,military affairs,and so on.In recent years,research of all-solid-state Raman lasers focuses on the following aspects:(1) By using the most common 1.06μm laser as pumping source,1.18μm first Stokes wavelength can be generated.(2) By frequency doubling technology,the 1.18μm can be converted to 590 nm,this is the yellow-orange laser.This laser source is of much interest for many applications in medical treatment,spectroscopy,information storage, lidar,atmosphere detection,and so on.(3) By using the 1.3μm laser as pumping source, 1.5μm eye-safe Stokes wavelength can be generated.The laser source of 1.5μm has wide applications in many fields such as radar,measurement,free space optical communications,and so on.So far,the researchers from Russia,USA,Australia and Taiwan are taking part actively in the field of the all-solid-state Raman lasers.China is renowned for the advanced crystal growth technology,and this provides favorable conditions to the study of all-solid-state Raman lasers in China.In the Chinese Mainland, the research groups from Shandong University,Nanjing University and Fujian Institute of Research on the Structure of Matter are engaged in the research of all-solid-state Raman lasers,and they have achieved some important results of research both theoretically and experimentally.In this dissertation,by using Nd:YAG and Nd:YVO₄ as the gain media,YVO₄, SrWO₄ and BaWO₄ as the Raman-active media,we make a detailed experimental study of the LD end-pumped and LD side-pumped intracavity Raman lasers.Based on the rate equations for the actively Q-switched intracavity Raman lasers,the reflectivity of the output coupler is optimized,under 1.06μm laser pumping,the highly efficient operation of 1.18μm Raman laser is achived.Under 1.3μm laser pumping,1.5μm eye-safe Stokes output is obtained.The main contents of this dissertation are as follows:1.Highly efficient operation of a diode-pumped actively Q-switched self-Raman laser,in which a c-cut Nd:YVO₄ crystal is used as the laser gain medium and Raman-active medium simultaneously,is realized.At a pump power of 5.0 W and a pulse repetition frequency(PRF) of 20 kHz,the self-Raman laser produces 910 mW of 1178 nm average output power.Diode-to-Stokes optical conversion efficiency is 18.2%,which is the highest LD-to-Raman optical conversion efficiency obtained by LD pumped intracavity self-Raman lasers.A maximum average output power of 1.4 W is obtained at an incident pump power of 9.0 W and a PRF of 60 kHz.2.By using Nd:YAG as laser gain medium and an a-cut SrWO₄ crystal as the Raman-active medium,the diode-end-pumped actively Q-switched Nd:YAG-SrWO₄ intracavity Raman laser is realized for the first time.At an incident pump power of 7.17 W and a PRF of 15 kHz,the obtained average output power at 1180 nm is 1.71 W, corresponding to a LD-to-Raman optical conversion efficiency of 23.8%.This is the highest conversion efficiency obtained by the LD pumped intracavitry Raman lasers.3.A diode-side-pumped actively Q-switched Nd:YAG/SrWO₄ intracavity Raman laser has been demonstrated,in which a Nd:YAG module is used as the fundamental laser source and a SrWO₄ crystal is used as the Raman-active medium to generate the first-Stokes laser at 1180 nm.A convex-plane cavity is employed to make the laser in a stable and efficient work under high pump power.At a LD pump power of 164 W and a PRF of 20 kHz,an average output power of 10.5 W at 1180 nm is obtained.To the best of our knowledge,this is the highest Raman output power at about 1180 nm obtained from a crystalline Raman laser.4.By using Nd:YVO₄ as the laser gain medium and BaWO₄ as the Raman-active medium,for the first time,the highly efficient LD-end-pumped actively Q-switched intracavity eye-safe Raman laser at 1532 nm has been realized.At an incident LD pump power of 12 W and a PRF of 35 kHz,an average output power of 1.5 W is obtained,corresponding to a LD-to-Stokes optical conversion efficiency of 12.5%, which is in the same level to the reported highest conversion efficiency of the LD pumped intracavity eye-safe Raman lasers.5.The influence of the LD pump spot size to the output characteristics of the intracavity eye-safe Raman lasers is investigated.When the fiber core diameter of the LD is 400 μm,the maximum average output power of the 1532 nm laser is 680 mW,when the fiber core diameter of the LD is 600μm,the maximum average output power of the 1532 nm laser is 1.5 W,and when the fiber core diameter of the LD is 800μm,the maximum average output power of the 1532 nm is 1.6 W.The main innovations of this dissertation are as follows:1.A LD-end-pumped actively Q-switched c-cut Nd:YVO₄ intracavity self-Raman laser is investigated and optimized.At a pump power of 5.0 W and a PRF of 20 kHz,the self-Raman laser produces 910 mW of 1178 nm average output power. Diode-to-Stokes optical conversion efficiency is 18.2%,which is the highest LD-to-Raman optical conversion efficiency obtained by LD pumped intracavity self-Raman lasers.2.For the first time,the highly efficient LD-end-pumped actively Q-switched Nd:YAG-SrWO₄ intracavity Raman laser has been realized.At an incident pump power of 7.17 W and a PRF of 15 kHz,the obtained average output power at 1180 nm is 1.71 W,corresponding to a LD-to-Raman optical conversion efficiency of 23.8%. This is the highest conversion efficiency obtained by the LD pumped intracavitry Raman lasers.3.For the first time,the LD-side-pumped actively Q-switched Nd:YAG-SrWO₄ intracavity Raman laser has been realized.At a LD pump power of 164 W and a PRF of 20 kHz,an average output power of 10.5 W at 1180 nm is obtained.To the best of our knowledge,this is the highest Raman output power at about 1180 nm obtained from a crystalline Raman laser.4.For the first time,the LD-end-pumped actively Q-switched Nd:YVO₄-BaWO₄ intracavity eye-safe Raman laser has been realized.At an incident LD pump power of 12 W and a PRF of 35 kHz,an average output power of 1.5 W is obtained, corresponding to a LD-to-Stokes optical conversion efficiency of 12.5%,which is in the same level to the reported highest conversion efficiency of the LD pumped intracavity eye-safe Raman lasers.