Crystal Growth And Characterizations Of The 2.8-3.1 Pm Ho³⁺Doped Laser Crystals

2.8-3.1?m mid-infrared lasers have important and broad applications in medical procedures due to their strong absorption by water,and this waveband lasers can act as pumping sources for the Optical Parametric Oscillator(OPO)to realize 3-15?m infrared laser output,which can be used in the fields of optoelectronic countermeasures,counter-terrist,and atmospheric detection,et al.Since 2.8-3.1?m lasers have important applications in the above several aspects,the new laser crystals doped with rare-earth ions as an important direction should be explored and researched for realizing the waveband laser output in future,which have been researched widely and deeply by many research institutions at home and abroad.At present,the mid-infrared lasers have been achieved through the rare-earth activated ions of Er3+,Tm3+ and Ho3+.In general,the laser transitions of the activated ions Er3+ and Tm3+ are mostly linear spectra.Therefore,it is difficult to realize specific wavelength laser within 2.8-3.1?m to suit the application requirements.By comparison,the Ho3+ ions acted as the activator exhibit the characteristic of broadband spectrum in the wavelength range of 2.8-3.1?m,which benefits to realize tunable laser output and can meet the application requirements of the specific wavelength laser,and the crystals doped with other rare-earth activated ions don't possess the characteristic.Thus,the mid-infrared lasers of the Ho3+ ions will be a development trend of the laser technology.We will investigate systematically the YAP and GYSGG crystals doped with the activated ions Ho3+ in this paper,combining the tunable property of the Ho3+ ions with the merits of the YAP and GYSGG hosts in order to take advantage of their respective characteristics.In addition,we take predecessors' research results as useful references.Single-doped Yb3+ ions or co-doped Cr3+,Yb3+ ions are used as the sensitizer for the activated ions HoMO in order to improve the pumping efficiency,and deactivator ions are also doped into the laser crystals to decrease the pumping threshold and improve the laser efficiency.In this paper,the main research contents and results are as follows.1.The Ho:YAP,Yb,Ho:YAP,Yb,Ho,Pr:YAP,Cr,Yb,Ho:YAP andCr,Yb,Ho,Eu:YAP crystals with high optical quality were grown successfully using the Czochralski method by optimizing the crystal growth parameter and technology.The structure and quality of these laser crystals were characterized.The results of X-ray powder diffraction(XRD)and X-ray rocking curves(XRC)indicate that the doped ions do not change the perovskite-like structure of the YAP host and the Ho3+doped YAP are single crystals with high crystalline quality,respectively.Additionally,we also analyzed the defects and their formation causes in the YAP crystals,which provide the basis and guidance for optimizing the growth technology to obtain high-quality single crystals.2.The fundamental physical properties of the Cr,Yb,Ho,Eu:YAP crystal were characterized,mainly including density,specific heat,thermal expansion coefficient,thermal diffuse coefficient,thermal conductivity,and Debye temperature,et al.And the thermal properties of the crystal along a,b,c crystalline axes changing with the temperature were analyzed.Results indicate that the thermal properties of the Cr,Yb,Ho,Eu:YAP crystal have the characteristic of anisotropy and the crystal along b crystalline direction possesses a lower thermal expansion coefficient and a higher thermal conductivity,which provide useful guidance for the crystal growth and its practical applications.3.The spectroscopic properties of the YAP crystals co-doped with the Cr3+,Yb3+,Ho3+,Pr3+ or Eu3+ ions were investigated,which mainly include the absorption spectra,fluorescence spectra and fluorescence lifetimes at room temperature.Moreover,the energy transfer processes among the doped ions were analyzed.Results show that the single-doped Yb3+ or co-doped Cr3+,Yb3+ ions can act as the sensitizer for the activated ions Ho3+,and Pr3+ or Eu3+ ions can play the role of deactivator to reduce efficiently the lifetime of the lower laser level.Therefore,Yb,Ho:YAP,Yb,Ho,Pr:YAP,Cr,Yb,Ho:YAP and Cr,Yb,Ho,Eu:YAP crystals are potential laser materials for the 2.8-3.1?m lasers.We also characterized the laser performance of these crystals.The laser output was realized on the Cr,Yb,Ho:YAP crystal pumped by the flash lamp for the first time.When the repetition rate is 5 Hz and the output coupler transmission is 30%,a maximum average power of 55 mW is obtained with the parallel-plane cavity.However,the laser output efficiency and power are relatively low,which remain further research.4.Using Cz method,a high optical quality Cr,Yb,Ho,Pr:GYSGG crystal with a size of 0 26 mm X 80 mm was successfully grown.The absorption spectra,emission spectra,and fluorescent lifetimes of the crystal were studied,and absorption coefficient,stimulated emission cross-section,and energy transfer efficiency were calculated.In addition,a single xenon flash lamp is taken as the pumping source,and the 2.84?m mid-infrared laser is realized on the Cr,Yb,Ho,Pr:GYSGG crystal with a plane-plane cavity for the first time.When the output coupler transmission is 5%,a minimum laser threshold of about 29.0 J and a maximum average power of 257 mW are obtained at a repetition rate of 5 Hz,corresponding to the electrical-to-optical efficiency of 0.033%and the slope efficiency of 0.040%.These results show that the Cr,Yb,Ho,Pr:GYSGG crystal is a new potential radiation-resistant gain medium for the mid-infrared lasers.This work provides reference for the development of new mid-infrared laser crystals Cr,Yb,Ho,Pr/Eu:YAP and Cr,Yb,Ho,Pr:GYSGG,and a foundation is alsolaid for their practical applications.