Theoretical And Experimental Study Of Ho³⁺:ZBLAN Fiber Laser Pumped By Red-Laser

With the development of visible lasers,green lasers have been widely used in medical,data storage,color display,precision processing and other fields.Among them,high-power,compact,stable and reliable green lasers have become a research hotspot of visible lasers.Since the early 1990s,the use of up-conversion technology to produce green lasers in Ho3+ion fluoride fiber has been reported,but the green power generated is not high(<50 mW).In this paper,the theoretical and experimental research on green light up-conversion Ho3+:ZBLAN fiber laser is systematically carried out.Using high-power red solid-state laser as the pump source,the experimental research of green tunable all-fiber laser and high-power green single-wavelength fiber laser were conducted respectively,and the spectral characteristics were calculated using Judd-Ofelt(J-O)theory also model the green light upconversion process by rate equations.The intensity of green light under different incident pump powers is specifically simulated.The theoretical analysis and experimental research are combined in order to explore a scheme for realizing high-power green light up-conversion laser output.The main research content includes the following parts:Ⅰ.The first part is mainly literature research,which paves the way for subsequent theoretical and experimental research.First,review the development process and application of fiber lasers,specifically introduce the realization of visible fiber laser technology,and the development and research status of Ho Ho3+:ZBLAN fiber in the realization of visible and infrared lasers;finally,introduce the mechanism of up-conversion technics in detail and calculation formula and application of J-O theory.Ⅱ.The absorption and emission spectra of Ho3+:ZBLAN fiber were measured,and their spectral characteristics were analyzed and calculated respectively.Based on the numerical analysis of the measured absorption spectrum,calculate the absorption coefficient,absorption cross section and the intensity parameters of the J-O theory,and then calculate the probability of each energy level transition from the three intensity parameters.The energy level lifetime of 5F4(5S2),5F5,5I5,5I6,5I7 and their corresponding fluorescence branching ratio of transition line.For the measurement of the emission spectrum,a home-made high-power red light(～640 nm)solid-state laser is used as the pump source,and the up-conversion emissio spectrum of the Ho3+:ZBLAN fiber is specifically measured.By analyzing the energy level transition corresponding to each emission peak,and then calculating the emission cross section of the energy level transition 5F4(5S2)→5I8(～550 nm)by the Füchtbauer-Ladenburg(F-L)formula,the above data is used to provide reliable data for the subsequent theoretical calculations.Ⅲ.Preparation of experimental materials for green fiber laser.Prepare Ho3+:ZBLAN optical fiber and ordinary quartz single-mode optical fiber(SMF)of different lengths through decoating,making optical fiber head,polishing and other processes,using plasma sputtering technology to directly coat the SMF end surface as green fiber laser.The coating parameters of the resonant cavity mirror of the conversion laser are as follows:the fiber input mirror MO is highly transparent to red light and highly reflective to green light(T=86.8%@640 nm,R=99.5%@550 nm),the fiber output mirror M1 M1 is highly reflective for red and partly transparent for green(R=80%@640 nm,T=14%@550 nm),respectively.Ⅳ.Green fiber laser experiment development and optimization plan.First,using MO and M1 to carry out the experiment of green tunable all-fiber laser,that is,the Ho3+ ion doping concentration is the same,choose Ho3+:ZBLAN fiber lengths of Lac=12 cm,17.5 cm and 25.5 cm,respectively,to achieve different green laser performance.When using Lac=17.5 cm,the maximum power of green laser is 120.7 mW,and the wavelength of green light is tunable in the range of 550-545 nm.Mainly due to the Stark energy level split between the 5F4(5S2)and 5I8 energy levels,this wavelength "blue shift" phenomenon is explained.At the same time,based on the calculated green laser gain spectrum,the green tunable results are theoretically analyzed.Next,a green laser resonator was constructed using a SMF high-reflector M0 and Ho3+:ZBLAN fiber end face with inherent Fresnel reflection(4%).Lac=17.5 cm and 29.6 cm were selected to carry out high-power green single-wavelength laser experiments respectively.To achieve stable operation of the green laser wavelength at 544 nm,and when Lac=29.6 cm,the maximum output power of green laser reaches 236 mW.Finally,the rate equation was established and the green up-conversion dynamics process is established to obtain the changes of population density of the 5F4(5S2),5I6 and 5I7 levels with the incident pump power.Comparing the emission intensity of the spectral lines at different pump powers,the theoretical simulation results are consistent with the experimental results,and summarize and propose an improved scheme for further realization of higher power green laser.