Growth And Laser Experimental Study At 2?m Of Tm³⁺:GYAP Laser Crystal

2?m lasers have been an important research field of solid-state lasers because of their particular characters.Firstly,there being strong absorption by liquid water,2?m lasers are eye-safe light sources that have been widely used in medical surgery.Secondly,2?m lasers have an important application in remote sensing and optical communications due to its strong penetration in the atmosphere,especially in coherent Doppler LIDAR system.Thirdly,high-power 2?m lasers can be used as an efficient pump source for Mid-IR 3?5?m optical parametric oscillators?OPO?.Therefore,high quality 2?m lasers source,especially 2?m ultrafast laser,has become the focus of current research.However,the traditional 2?m lasers crystal material has orderly lattice structure and narrow emission spectrum,which makes it difficult to realize ultrafast laser.By doping ions to replace the original one or more ion in crystal material,the crystal's lattice structure is changed,which causes laser energy level splitting up and down to form a broader laser spectrum,and to realize the ultrafast laser output.In this paper,the growth of disordered laser crystal of Tm3⁺:GYAP was firstly proposed,and the growth of disordered single crystal GYAP and the factors affecting the growth quality were discussed.The disordered crystal of Tm3⁺:GYAP emitting laser at 2?m band was successfully grown,and the optical properties of the crystal were characterized.We report here on the diode-pumped continuous-wave and passively Q-switched laser operation of Tm3⁺:GYAP in this specific wavelength domain,for the first time to our knowledge.The experimental results show that the disordered laser crystal of Tm³⁺:GYAP has a wide fluorescence spectrum and a large emission cross section,which confirms that the Tm³⁺:GYAP crystal has the potential to realize 2?m band ultra-fast laser.In this work,the main research contents and results are as follows:1.The GYAP monocrystals with disordered structure were grown by Czochralski method with high purity?99.999%?raw materials?Gd₂O₃???Y₂O₃?and?Al₂O₃?and the whole growth process was introduced in detail.By XRD measuring,the structure of GYAP is the same as that of YAP single crystal and belongs to Pnma space group.2.The Tm³⁺:GYAP monocrystals,whose cell parameters are fitted to be a=5.321?,b=7.371 ?,c=5.176?,were grown by Czochralski method.Polarized absorption spectra of Tm³⁺:GYAP includes peak at 794 nm,which matches well with the emission of the commercial LD pumping such as Al Ga As.The J-O intensity parameters were calculated to be ?₂=2.20×10^-20 cm²,?₄=1.74×10^-20 cm²,and?₆=1.60×10^-20 cm².The values of absorption peak along crystallographic a,b,and c axes are determined to be 0.47×10^-20cm² ?at 797 nm?,0.55×10^-20cm²?at 777 nm?,and 0.41×10^-20cm²?at 794 nm?,respectively.The FWHM of the fluorescence spectra in Tm³⁺:GYAP crystal along crystallographic a,b,and caxes are fitted to 189 nm,202 nm,and 203 nm.The maximum stimulated emission cross- sections along crystallographic a,b,and c axes of the Tm³⁺:GYAP crystal are 0.80×10^-20 cm²?at 1956 nm?,0.70×10^-20 cm²?at 1903 nm?,and 0.43×10^-20 cm²?at 1935 nm?,respectively.These characteristics are conducive to ultra-fast laser output.3.The experiments of laser output characteristics of Tm³⁺:GYAP?2 at.%?and Tm³⁺:GYAP?5 at.%?crystals in the continuous-wave regime were tested.For Tm³⁺:GYAP?2 at.%?crystals,the maximum output power was 426m W,corresponding to the optical-to-optical efficiency of 6.4%and the line-polarized extinction ratio of 15.19db.For Tm³⁺:GYAP?5 at.%?crystals,the maximum output power was 3.52W,corresponding to the optical-to-optical efficiency of 33.9%,the slope efficiency of 43.7%,and the line-polarized extinction ratio of 15.19d B.And the laser polarization direction of Tm³⁺:GYAP is the same as the crystal c axis.4.Using a graphene saturable absorber,passive Q-switching is achieved with a maximum average output power of 0.946W.The narrowest laser pulse width is found to be about 492 ns for a repetition rate of 4.05 k Hz and the corresponding laser pulse peak power and pulse energy are about 474.8W and 239.7?J,respectively.