Research On 2 Micro-meters Of Solid-state Raman Lasers

Stimulated Raman Scattering?SRS?has been one of the most important nonlinear frequency conversion methods due to its practicality and effectiveness in the field of all-solid-state lasers.In addition,SRS can generate laser output at new wavelength,ranging from ultraviolet to mid-infrared,and has high conversion efficiency,which greatly contributes to expanding the spectral range of the laser.Since the Stokes and anti-Stokes Raman Scattering in crystal was first observed,the efficiency of Raman conversion is limited for a long time because of the quality and variety of crystal.In recent decades,with the emergence of new high-performance laser crystal,the efficiency of Raman conversions were increased greatly.All-solid-state Raman lasers have become the research focus due to the advantages of compactness,high efficiency and high stability.In the past few years,research about solid-state Raman laser concentrated on the 1-1.8?m rang.Solid-state Raman laser over 2?m wavelength were seldom reported because the decrease of Raman gain coefficient rapidly with increasing Stokes wavelength.The laser at 2³?m has wide application prospects in remote sensing,gas molecular detection and environmental monitoring due to its spectrum coincides with the absorption line of many gas molecules.Tm:YLF crystal is suitable for diode pumping because of its low tendency to thermal lensing and long upper-state life time.Vanadate crystals YVO₄and GdVO₄ are both excellent Raman crystals,which can be used as a Raman frequency shifter for lasers at the visible and near-infrared wavelength region.The main contents of this thesis are as follows:I According to the transmission matrix theory,the influence of crystal thermal lens effect on the stability of the cavity was analyzed and calculated.the resonator of the Raman laser was numerically simulated by tanking into account of the thermal effects of laser crystal,the relations between resonator stability and the parameters of cavity,such as the length of cavity,the type of mirror.The numerical simulation and analysis can be used as a reference for the experimental research.II A diode-end-pumped Tm:YLF/ZnWO₄ Raman laser based on folded cavity is demonstrated.The maximum average output power of Raman laser obtained was108.4mW.The shortest pulse width,the maximum pulse energy and the highest peak power were measured to be 10.55 ns,21.68?J and 2.05 kW,respectivelyIII we report a diode-end-pumped actively Q-switched YVO₄ Raman laser at 2291nm.A Tm:YLF crystal and a pure YVO₄ crystal were used as the laser and Raman media,respectively.With an output coupler with transmission of 10%in the range of 2250-2580nm,the average output power,pulse energy,and pulse width as the function of incident pump power were investigated.The maximum average output power at 2291 nm was up to 175.2 mW at the incident pump power of 21 W and the PRF of 5 kHz.The corresponding pulse width and single pulse energy of the first Stokes are approximately 21.41 ns and35.04?J.IV We report a diode-end-pumped Tm:YLF/YVO₄ Raman laser based on four-mirror-folded?U-configuration?resonator.The maximum average output power of Raman laser at 2287 nm obtained was 261 mW at the incident pump power of 22W and at a repetition rate of 5kHz,corresponding to the optical conversion efficiency of 1.1%.The shortest pulse width,the maximum pulse energy and the highest peak power were measured to be 16.59 ns,52.2?J and 3.14 kW,respectively.