| Laser is one of the greatest inventions in the 20th century.The wide application of laser has completely changed people's life and brought great social and economic benefits.Among them,high power ultra fast laser is one of the important directions of laser technology development at present.These characteristics short pulse and high peak power of ultra-fast laser make it widely used in many fields.For example,short pulse widths have important applications in stimulating and measuring ultrafast physical processes in solid and biomaterials,and high peak power makes them have important application prospects in precision machining,scientific research and medical treatment.Regardless of the generation or amplification of ultrafast laser,the key element is the laser gain material.The spectral width of the laser gain material determines the pulse width that can be generated,and its thermal properties determine the achievable laser power and efficiency.Therefore,since the invention of laser in the 1960s,the research on new laser gain materials has received extensive attention.Generally,the luminescent properties of the gain materials are mainly attributed to the activated ions and are affected by the local coordination field in the matrix crystals.While the thermal properties of the gain materials are mainly determined by the matrix crystals and are simultaneously affected by the activation ion doping.For high power ultra-fast laser,narrow pulse width can be achieved with wide emission spectrum,while matrix crystals with high thermal conductivity and low sub-energy are beneficial to obtain high efficiency and high power laser output.The activated ion-doped sesquioxide crystals have high thermal conductivity and is an important gain materials for high power ultrafast pulsed lasers.However,limited by its high melting point(2400?),its research is still in initial stage,especially the relationship between structure and spectral properties needs to be revealed.For a long time,our research group has been engaged in the study of sesquioxide crystals,and have successfully grown the sesquioxide(Lu2O3)single crystals by the optical floating zone(OFZ)method.On this basis,this paper focuses on the Yb3+ ion-doped novel sesquioxide LuxSc2_xO3(0?x?2)and LuxY2-xO3(0?x?2)mixed crystals.Based on the Jahn-Teller effect and considering the electron-phonon coupling effect,the spectral width of Yb3+doped sesquioxide crystals is broadened about 3 times broader than Yb:YAG,and the wavelength range cover 900?1200 nm.The related studies provide useuful reference for the study of sesquioxide crystals and even other laser crystals.The main findings are as follows:1.Growth and Structural Characterization of Sesquioxide CrystalsThe sesquioxide crystals have extremely high melting point over 2400?.The studies on crystal growth of series of sesquioxide crystals are carried out by optical floating zone method on the basis of previous studies.By optimizing the growth rate,rotational speed,growth atmosphere,cooling rate and t annealing,the high-quality sesquioxide single crystals are successfully grown,which solved the problems of cracking and color center during crystal growth.Fourteen components of Yb:LuxSc2-xO3 crystals including 1 at.%and 5 at.%doping concentrations were grwon.And six components of Yb:LuxY2-xO3 crystals with 1 at.%doping concentrations are grown.The maximum size of the as grown crystal reaches ?9.3×67mm3.The composition and the structure of single crystal are tested and analyzed,and the series of structural information of ligand and cell parameters are revealed.2.Study on Spectral and Thermal Properties of Sesquioxide CrystalsThe spectral properties of the crystals are mainly attributed to the activated ions and are affected by the coordination environment in which the activated ions are located.Through the study of the distortion of octahedral ligands and the relationship between phonon vibration and crystal components,it is found that the inhomogeneous broadening caused by local ligand distortion and the broadening caused by electron-phonon coupling effect are the main reasons for the spectral broadening.The maximum spectral broadening is achieved in Yb:Lu1.5Sc0.5O3 crystals with a result of 28.2 nm at around 1035 nm,and the spectral width reaches 30.2 nm at around 1080 nm;The dipole moment is calculated to characteristic the inhomogeneous broadening effect of spectrum caused by the distortion of ligand.The crystals with the largest spectral width are found by low temperature spectrum.On basis of result,the optimal crystal components at room temperature were found by calculating the ionicity and matrix mass difference factors of sesquioxide crystals to characterize the spectral broadening caused by the electron-phonon coupling effect.The thermal properties of Lu2O3 crystals are insensitivity to Yb3+ions doping,due to the similar radius of Lu3+ ions and Yb3+ions.Meanwhile,the ionic radius of Lu3+is similar to that of Y3+ions,therefore,the good thermal properties and the insensitivity to Yb3+ions doping are maintained when Lu3+and Y3+form solid solutions,while the spectral broadening is achieved.The maximum spectral broadening is achieved in Yb:Lui.19Y0.81O3 crystals at room temperature,and the spectral width at around 1030 nm reaches 24.55 nm.And the radius of Y3+ ion is larger than the radius of Sc3+ ion,so the phonon average free path of the Yb:LudY2-xO3 crystals is larger than that of the Yb:LuxSc2-xO3 crystals,resulting a higher thermal conductivity.The thermal conductivity of Yb:Lu0.99Y1.01O3 crystals reaches 5.488 W/mK,which is higher than that of 1 at.%Yb:LuSc03 crystals.Moreover,the mass of the Y3+ion is larger than that of the Sc3+ion,so the vibration of the Y-O bond is smaller than that of the Sc-O bond.Therefore,the Yb:LuxY2-xO3 crystal will have smaller phonon energy,which can effectively reduce the probability of radiation-free transition,suppress the heat generated by radiation-free transition,which makes it have potential application in high power ultrafast laser.3.Study on Laser Properties of Sesquioxide CrystalThe continuous laser output of 5 at.%doped Yb:Lu1.1Sc0.9O3 crystal and 1 at.%doped Yb:LuScO3 crystal are realized.The 571 mW continuous laser is obtained in 5 at.%doped Yb:Lu1.1Sc0.9O3 crystal with a wavelength of 1086 nm,and a slope efficiency of 43%.After optimizing the doping concentration,using a output couping mirror T=3%,10.41 W continuous laser is obtained in 1 at.%doped Yb:LuScO3 crystal,with a wavelength 1036 nm and a slope efficiency 67%.When the transmittance of output coupling mirror is 1%,the wavelength of the continuous laser is 1086 nm,which is because the emission peak at 1086 nm starts first when the gain is low,while the emission peak at 1036 can start and occupy the dominant position only when the gain is high.Using Cr4+:YAG as a passive optical switch,the passive Q-switched pulse laser is realized in the 1 at.%Yb:LuScO3 crystal with a minimum pulse width of 7.3 ns,a maximum pulse energy of 394 ?J and a maximum peak power of 49.44 kW. |
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