Research On High Power Diamond Raman Laser Brightness Enhancement Technology And Diamond Brillouin Laser

As important tools,high-power lasers act an irreplaceable role in industrial manufacturing,space exploration and national defense.In addition to realizing highpower operation,researchers are also struggling with obtaining high brightness,narrow linewidth and different wavelengths output for different applications.However,due to the limitation of the intrinsic thermal capacity in currently available laser materials,with the increase of pump power,the increasing thermal effect often leads to the beam quality distortion that decreases the output beam brightness.These negative effects also limit the application of high-power lasers in the fields of directional energy and space detection that require long-distance propagation of the beam.Moreover,generating high-power lasers with the specific wavelength is also critical to some certain application,for instance,1.5 ?m wavelength range lasers at the human eye-safety band and atmospheric window playing an excellent role in radar,remote sensing.Brillouin laser is one of the main technical means to obtain the laser output with narrow linewidth.Currently,Brillouin lasers reported are generated in the waveguide and microcavity formats to facilitate Brillouin amplification,which restricts the output wavelength and power of Brillouin lasers to a large extent.The Brillouin frequency combs(BFCs)with a frequency interval of 10 GHz have important application prospects in the field of spectroscopy and microwave photonics,however,those BFCs also generated in waveguide and microcavity structures showing lower power.Diamond possesses high thermal conductivity,wide spectral transmittance and high Raman gain coefficient,making diamond Raman laser(DRLs)exhibit excellent performance in wide spectral range(from ultraviolet,visible to infrared),and under the condition of both pulsed and continuous-wave(CW)pumping.At the same time,diamond has high acoustic wave propagation speed and wide band gap,which make diamond a promising candidate to be applied as a Brillouin medium and expected to improve the performance of Brillouin devices.In my study,diamond is used as Raman and Brillouin gain media.A large-scale brightness enhancement in high-power pumped DRL,and the free-space Brillouin laser and BFC are developed.1.The research status and trend of DRLs,high power 1.5 ?m lasers,Brillouin laser and Brillouin optical frequency comb are discussed.The output power comparition of DRLs and other types of Raman lasers,as well as the characteristics of different Brillouin gain medium,are discussed.2.Both the optical and thermal properties of diamond are analyzed.Based on the theoretical models of stimulated Raman scattering(SRS)and stimulated Brillouin scattering(SBS),the parameters affecting the performance of the DRL and diamond Brillouin laser(DBL),as well as experimental design method are discussed.3.A quasi-CW Nd:YAG laser with beam quality factor adjustable from 1.5 to 7.3 is used as the pump source.The Stokes output of the near-diffraction-limit is obtained through all pump situations in the external-cavity DRL with maximum on-time output power of 390 W and the maximum brightness enhancement factor of 12.7.Meanwhile,the steady-state Raman laser model is established to analyze and predict the Raman threshold,output power and brightness performance of DRLs when pumped in more degenerated pumping conditions.4.A near-diffraction-limit 302 W quasi-continuous cascaded DRL at 1.5 microns with brightness enhancement factor up to 6.0 is demonstrated pumping with a quasicontinuous Nd:YAG laser.By using the steady-state cascade Raman model,a scheme to further optimize the design of cascaded DRLs to improve conversion efficiency and brightness enhancement factors is proposed.It provides a new path for achieving high-power laser output at different wavelengths by using cascaded DRLs.5.The Brillouin laser is realized by directly pumping a high-finesse linear DRL cavity,and for the first time,the BFC is obtained in the diamond with the number of frequency lines as high as 19.By using an active cavity locking technology in the power enhanced ring-cavity,the free-space DBL has been developed while pumped by a single-frequency laser and the Brillouin gain coefficient of diamond is measured.In addition,a new Brillouin gain linewidth measurement technique based on frequency tuning is proposed and applied in the Brillouin gain linewidth measurement of diamond.The results show that diamond has great potential to be harnessed in Brillouin devices for high-power,wider wavelength range and high acoustic frequency in the future.