Study Of Direct Pumped Er:YSGG Crystal Green Laser Based On Seed Injection

Green laser(520?560 nm)is playing an increasingly important role in Surgical treatment,marine scientific research,display imaging,UV lasers and equipment manufacturing because of its high brightness,high color purity,small focused spot and low heat affected interval.At present,there were three main ways to realize green laser:Direct pump excitation green laser,semiconductor PN junction excitation of green laser and nonlinear optical conversion to generate green laser.Direct pump excitation of green laser was achieved by pumping substrates with doped rare-earth ions such as Er³⁺,Tm³⁺and Ho³⁺to exploit the properties of the rare-earth ion up-conversion leap to achieve green laser emission.Semiconductor PN junction was through the growth of direct band gap semiconductor materials to make its forbidden band width to meet the energy band requirements required for green laser excitation to achieve green laser emission.Non-linear optical changes to produce green laser was currently the more common method,through solid-state lasers such as Nd:YAG or Nd:YVO₄ to produce 1.06?m laser and then by frequency doubling crystal KTP or LBO to produce green laser.Semiconductor PN junctions had the advantage of producing green light directly but had strict requirements for material growth.Nonlinear optical variations had extremely high matching requirements for the energy conversion of the fundamental and second harmonic beams because of the need to match the nonlinear region of the frequency doubling crystal,which increased the complexity of the system.The direct pump excitation of green laser was difficult because the down-conversion laser emission threshold was lower than the up-conversion laser emission threshold and the low conversion efficiency led to green light emission.In this paper,a new idea of direct pumping Er:YSGG crystal to achieve up-conversion green laser emission was proposed.Combining the design features of solid-state lasers and dye lasers.A semiconductor laser is used as the pump source to enhance the energy level transition property of Er³⁺ions located at ⁴S_3/2?⁴I_15/2 in the case of using external seed light injection.Firstly,the amplification in the green light band(553?559 nm)was achieved.After that,the direct emission of the green laser at room temperature was achieved by changing the design of the optical path and resonant cavity structure.This paper mainly does the following work:(1)We analyzed the energy level leaping mode of the up-conversion luminescence of Er:YSGG crystal by theoretical study,characterized the absorption emission properties of Er:YSGG crystal,and determined the emission wavelength of up-conversion green light by combining theoretical and test data.(2)To match the emission wavelength of converted green light on Er:YSGG crystals,the basic optical properties of the laser dye sodium fluorescein were characterized,the physical and chemical properties of different concentrations of sodium fluorescein solutions were tested,the amplified spontaneous emission(ASE)properties of each concentration were analyzed,and the final concentration of the seed light solution used was determined.(3)An optical amplification test system was built to test the amplification capability of Er:YSGG crystal for green light band and to analyze the effect of different doping concentrations of Er³⁺ions on its amplification capability.(4)A green laser oscillation system was built,and the resonant cavity was adjusted to optimize the mode matching between the seed light and the pump light.The optical properties of the emitted green laser were characterized,and the effects of different doping concentrations of Er³⁺ions on the characteristics of the green laser were analyzed.With the combination of theory and experiment,the tunable amplification capability of Er:YSGG in the green wavelength band of 6 nm was obtained with amplifications reached a maximum of 4.7d B and 4.5 d B,respectively.finally,the converted green laser output of Er:YSGG crystals on direct pumping at 555.72 nm and 556.76 nm was achieved.