Exploration Of Pr³⁺ Ion Doped Laser Crystals And Their Pulse Laser Characterization Pumped By Blue Semiconductor

Visible laser refers to the laser with a wavelength of 400-760 nm,which is the basic light source in the fields of entertainment,lighting,processing,medical treatment.At present,semiconductor lasers and frequency doubling of the near infrared lasers are two main technologies for generating visible lasers.In recent years,with the advancement and de'velopment of GaN-based semiconductors,blue semiconductors have matured and become practical.In 2014,the Nobel Prize was awarded to three Japanese scientists in recognition of their work on blue light semiconductors.Then,it has become an emerging direction in laser fields to realize all-solid-state lasers directly pumped by blue semiconductor lasers.As a typical representative of rare earth ionic,Pr3+ ion doped laser crystals become an important blue-pumped all-solid-state visible laser materials because of its absorption of blue light and emission of multi-wavelengths from green to red.However,Pr3+ ion doped laser crystals that can realize the laser output should have the low phonon energy like fluoride.It is necessary to develop basic theories to reveal the key scientific issues that limit the laser effect of Pr3+ ion doped laser crystals,which can serve as a guide for the development and application of laser crystals and laser technologies in the future.In laser technology,in addition to pump sources and laser crystals,optical switch components,including Q-switchers and mode-lockers,are key components for laser pulse modulation.As an emerging laser technology,the research on optical switch components is limited and needs to be developed for the directly pumped by blue semiconductors in the visible range,especially the passive optical switch components in the visible range.The wavelength of visible laser is relatively short corresponding to a relatively large photon energy,generally,the gain of the laser crystals in the visible range is relatively low.These have put forward unique requirements for the visible range saturated absorbers in terms of material bandgap,carrier recovery time,saturable absorption intensity and modulation depth.Therefore,the development of selection criteria for the visible range optical switchers and the realization of pulse lasers play an important role in the development and application of this emerging laser technology and device.Considering the development of visible lasers directly pumped by blue semiconductors and aiming at the Pr3+ ion doped laser crystals and optical switchers in the visible range,this paper studies the key physical parameters that limit the laser output of Pr3+ ion doped laser crystals.The influence of the nonradiation transition on the visible laser output is revealed.These researches can provide theoretical references for the study of visible lasers with Pr3+ ion doped laser crystals as the gain materials.Based on the rate equation,the selection criterion of the visible Q-switchers is derived.The conditions that the visible Q-switchers need to be met are found.Based on this selection criterion,the nonlinear saturable absorption properties of graphene materials and Co:ZnO thin film are tested.The feasibility of the two materials as Q-switchers is predicted in the visible range,and the Q-switched pulse lasers at different visible wavelengths are realized.The selection criterion of mode-lockers in the visible range is established and the key physical parameters that limited the applications of mode-locking in the visible range are found,and the selection criterion is verified on behalf of M0S2 materials and graphene materials.Mode-locked pulse lasers at different visible wavelengths are realized.Based on the Kerr-lens mode-locking principle,self-mode-locked pulse laser is realized in the visible range.Combined with the dispersion compensation technology,the shortest pulse lasers pumped by the blue semiconductor is obtained with a pulse width of 1.1 ps.The main research contents of this paper are as follows:First,theory of Pr3+ ion doped laser crystals in the visible rangeStarting from the distribution of Pr3+ ion energy level,the four-level rate equation of Pr3+ ion was deduced and established with the consideration of the nonradiative transition process between the 3P0 and 1D2 energy levels.In view of the effect of the nonradiative transition probability between the 3Po and ID2 energy levels on the generation of laser,the effect of phonon energy and energy level splitting in the visible laser was deduced.The key factors of Pr3+ ion doped laser crystals for generating visible range lasers were found to be the energy level splitting and phonon energy.The physical relationship between energy level splitting and phonon energy was established.This work may provide a theoretical reference for the study of Pr3+ ion doped laser crystals.Second,selection criterion of Q-switchers and research on Q-switched pulse lasers in the visible range1.Starting from the rate equation,the selection criterion of Q-switchers was developed.Based on the spectral parameters of the Pr3+ ion doped laser crystals,the conditions for the Q-switchers in the visible range were estimated.Selection criterion of visible range Q-switchers was developed to guide the selection of Q-switched materials in the visible range.2.Taking the two-dimensional material graphene and 3dN ions Co:ZnO as representatives,the nonlinear saturable absorption properties of monolayer graphene and Co:ZnO were measured in the visible range.According to the selection criterion of Q-switchers in the visible range,the feasibility of two materials was predicted for their applications in the visible pulse lasers.Based on the continuous lasers of Pr3+:YLiF4 crystal,Q-switched pulse lasers at different wavelengths were realized with the above two materials as Q-switchers in the visible range.Third,selection criterion of mode-lockers and research on mode-locked pulse lasers in the visible range1.The selection criterion of the mode-lockers was developed based on the rate equation.According to the spectral parameters of the Pr3+ ion doped laser crystals,the selection criterion of mode-locked materials in the visible range was constructed,and the key physical parameters affecting the mode-locked laser effect were revealed.It is proposed that the mode-lockers in the visible range needs to have three conditions:the bandgap of the saturable absorber?1.7 eV,the carrier recombination life?10 ns,and the saturation energy density and the modulation depth product Fsat.A?R?2 nJ/cm2.2.The nonlinear saturable absorption properties of different layers MoS2 materials were systematically tested.Guided by the selection criterion of mode-lockers in the visible range,less than ten layers MoS2 materials were predicted for the applications as the visible range mode-lockers and the conclusion was verified experimentally.Mode-locked pulse lasers at different wavelengths were obtained with the selected MoS2 materials.The nonlinear saturable absorption properties of monolayer graphene were tested and characterized in the visible range and the key physical parameters were calculated.It finds that monolayer graphene meets the selction criterion of visible range mode-lockers.Monolayer graphene was used as the mode-locker in both transmissive and reflective modes and different visible wavelengths mode-locked pulse lasers were obtained for the first time in the visible range.Fourth,research on Kerr-lens mode-locked lasers in the visible rangeTaking Pr3+:LuLiF4 as the research object,based on the characteristic of large nonlinear refractive index,the laser cavity of Kerr-lens self-mode-locking was designed according to the ABCD matrix.The dispersion curves of key components in the cavity were calculated.Self-mode-locked pulse laser of the Pr3+ ion doped laser crystal directly pumped by the blue semiconductor was realized with the help of ZF4 prism pair.The relevant research result is the shortest pulse laser output in the visible range with the semiconductor as the pump source.In summary,"three criteria" of crystals and optical switchers in the visible range are developled based on the development status of blue semiconductors pumped Pr3+ion doped laser crystals and laser devices.These criteria may provide useful references for the development of laser crystals and devices in the visible range.In this paper,the maximum output power of continuous visible laser under single-tube blue semiconductor pumping is obtained,and the device design of Q-switched and mode-locked pulse lasers is realized.The shortest ultrafast mode-locked laser of Pr3+ ion laser crystal is obtained with blue semiconductor as the pump source.