清华激光原理ppt课件.ppt

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1、第7讲四能级系统单模速率方程的建立多模速率方程的建立均匀加宽工作介质的增益系数从速率方程出发推导小信号增益系数表达式小信号增益曲线增益线宽均匀加宽工作介质的增益饱和大信号增益系数、强光作用下的弱光增益系数非均匀加宽工作介质增益系数作业：4-7、4-13、4-201pump21laserlaserlaserTwo,three,fourlevellasers21032132102He+eHe*21S0，23S1He*+NeNe*+He+DE100ns10ns与管壁碰撞铒离子能级图0.98nm3§4.3Rateequationsexamples(th

2、ree,fourlevelssystem)DifferentialequationsdescribingthedynamicsofpopulationandphotondensityofvariouslevelsPhysicalbasicforrateequations:EinsteinrelationshipRedruby,Er3+dopedfiberw13A31S31S32A21S21w21w12E1E2E3He-Ne,Nd:YAG较大w03A30S30S32S21A21W21E3E2E1E0W12S10××41.Fourlevelssyste

3、m1)singlemodeoscillation(lthmode,n)w03A30S30S32S21A21W21E3E2E1E0W12S10没有包括A21引起的光子数？(ignoreS30)（4.4.13）5RateequationsforpracticallaseraresetupaccordingtothevariousphysicalprocessesDifferentexpressionsofrateequationsforasamelaserR1,R2isatomdensitypumpedpersecondintoE1andE2,resp

4、ectively.t1,t2islifetimeatE1,E2,respectively;t21isspontaneousemission(荧光fluorescence）lifetimeforE2E1.E2E1R2R1t2t1t21ConsiderlossonlyPhotonlifetime光子寿命（2.1.14）Lasertransition6E2E1R2R1t2t1t21PumptransitionsLasertransitionw03A30S30S32S21A21W21E3E2E1E0W12S1072)Rateequationsformul

5、timodeoscillationSerialnumberofmodeFrequencyofmodePhotonnumberofserialmodeMethod:对应每个模式分别建立一个速率方程,序数相应变化8SimplificationsLineshapefunctionrectangle(矩形)Sameloss,samelifetimeofphotonforeachmode矩形面积＝原谱线面积ReasonsofsimplificationDonotneedtoconsiderdifferencesofthemodesforstudyingq

6、uestionNeglectthedifferenceofdiffractionlossinthemodesAccordingtotheabovesimplifiedmodel,multimoderateequationsforfourlevelssystemasfollowing9N–totalphotondensityforallmodes泵浦效率Multimoderateequationsforfourlevelslasersystem荧光量子效率w03A30S30S32S21A21W21E3E2E1E0W12S1010Pumpingeffi

7、ciency:thefractionofthetotalpumppowerthatisusefulincreatingthepopulationinversionFluorescence(quantum)efficiencyfromE2E1,dependssolelyoncharacteristicsofmedium,itistheupperlimitforperformanceofanylaser.w03A30S30S32S21A21W21E3E2E1E0W12S10Totalquantumefficiency(总量子效率)发射荧光的光子数从光

8、泵吸收的光子数（Photonnumbersofemittingfluorescence）（Photonnumbersabs