Study On The Growth And Performance Of LuAG Single Crystal Fiber By Micro-Pulling-Down Method

With the continuous improvement of the demand for the development of today's science and technology,artificial crystals play a vital role in many fields,so they have attracted more and more attention from people.Compared with natural crystals,the biggest advantage of artificial crystals is that they can artificially control the crystal growth process to obtain crystal materials that meet actual application requirements.Single crystal fiber is an artificial crystal material with a relatively short development time.It combines the excellent characteristics of traditional bulk crystals and the shape advantages of glass fibers.It has high thermal conductivity,stable physical and chemical properties,good thermal management performance and good optical properties.It can effectively reduce the overheating effect in the crystal application process,but also help realize the miniaturization of the device,so it is a new and excellent optical material.Although the micro-pulling-down technology was formed relatively late,it has become one of the most important mainstream methods for the growth and preparation of single crystal fibers.The single crystal fibers grown by the micro-pulling-down technology usually have low thermal stress,uniform doping ion distribution,and high optical quality.At present,single crystal fiber related devices have begun to gradually realize industrialization research,and the United States has conducted research on single crystal fiber defense weapons as early as 2015,and Japan,France,Italy and other countries also have rich research experience on single crystal fiber.Compared with foreign countries,the domestic research and exploration of single crystal fiber started late,and there is a large room for improvement in basic theoretical knowledge,equipment development,fiber preparation technology and final device application.Therefore,the research on single crystal fiber is of great significance.As a garnet structure crystal,LuAG belongs to the cubic crystal system,Ia3d space group.It has excellent thermal and optical properties,stable physical and chemical properties,high laser damage threshold,large emission cross-section area and optical isotropy.It is an ideal substrate material for solid-state laser and temperature sensing.The Yb3+doped LuAG single crystal fiber is an ideal solid-state laser gain medium for high-power lasers in the 1 ?m band.At present,France and Italy have reported the laser performance of Yb:LuAG single crystal fiber,but the laser output power and slope efficiency are low.There is no research report on the laser performance of Yb:LuAG single crystal fiber in our country.Therefore,this paper studies the growth and laser performance of Yb:LuAG single crystal fiber,and finally obtains the highest laser output of Yb:LuAG single crystal fiber.For the first time,the Er3+and Yb3+co-doped LuAG single crystal fiber prepared by micro-pulling-down method as the thermal probe of temperature sensor.And the up-conversion fluorescence intensity ratio temperature measurement performance of Er,Yb:LuAG single crystal fiber was studied.It is proved that Er,Yb:LuAG single crystal fiber is a promising optical temperature sensing material.The specific research contents of this paper are as follows:The first chapter introduces the research background and basic theoretical knowledge of this paper in detail,including the concept and development of single crystal fiber,the growth method of single crystal fiber,laser gain medium,fiber temperature sensor and up-conversion luminescence mechanism,etc.In the end,the significance,research purpose and content of this paper are briefly described.In the second chapter,the growth process of high quality Yb:LuAG laser single crystal fiber is introduced,and the basic properties of the grown single crystal fiber are characterized systematically and comprehensively.The solid-phase synthesis method was used to prepare polycrystalline raw materials,and directional seed crystals were used to prepare high-quality Yb:LuAG single crystal fibers by micro-pulling-down technique.The laser micrometer was used to characterize the fiber diameter fluctuations.The orientation and crystallization quality of the Yb:LuAG single crystal fiber were measured by Laue diffraction.The third chapter mainly studies the spectral performance of Yb:LuAG single crystal fiber and verifies the laser performance of Yb:LuAG single crystal fiber.The absorption spectrum data in the wavelength range of 880?1050 nm at room temperature is collected,which provides a basis for the selection of the pump source.The fluorescence emission spectrum of Yb:LuAG single crystal fiber in the range of 950?1200 nm was tested,and the fluorescence emission peak of about 1 ?m was obtained.The corresponding fluorescence lifetime was calculated,which proved that Yb:LuAG single crystal fiber has great potential to realize laser output in 1 ?m wavelength.The single crystal fiber continuous laser experiment was designed,a 940 nm laser diode was used as the pump source to obtain a maximum continuous laser output of 4.7 W with the center wavelength at 1049 nm.The beam quality factor M2 at the highest laser output power are close to 1 in both directions,which proves the higher laser output quality of Yb:LuAG single crystal fiber.Chapter 4 introduces the high-quality 0.5%Er,5%Yb:LuAG single crystal fiber grown by the micro-pulling-down technique,and explores its up-conversion fluorescence temperature sensing performance.The grown Er,Yb:LuAG single crystal fiber was ground into powder for XRD test to characterize the phase and crystal quality.For the first time,the LuAG single crystal fiber co-doped with Er3+and Yb3+ions was used as the thermal probe of the temperature sensor.The up-conversion fluorescence spectroscopy test experiment was designed with a 976 nm laser diode as the pump source to study the the fluorescence emission spectrum changes of different pump power and temperature.And the up-conversion fluorescence intensity ratio temperature measurement performance has been preliminary studied.The relationship between the integrated fluorescence intensity ratio of the corresponding bands of the two thermally coupled energy level transitions and temperature conforms to Boltzmann's formula.The obtained 0.5%Er,5%Yb:LuAG has a maximum relative sensitivity of 0.017 K-1 in the temperature range of 298 K to 898 K,which proves its application potential in the field of optical fiber temperature sensing.The fifth chapter summarizes and elaborates the main content,innovation and the work to be carried out of this thesis.