激光基本原理共振腔内放发光材料,用光源对它泵浦,(称为原子激发态平均寿命)很短,,腔内“相同”的光子数目加倍;如此循环,腔内“相同”,比损失的数量还多,,处于高能态的原子数比在低能态原子数目多(称为粒子数反转)。PropertiesofLaserlight属性(1).Monochromaticity单色性erlightisconcentratedinanarrowrangeofwavelengths,.(2).CoherenceTwotypesofcoherence:.(3).DirectionalityBeamdivergence(发散)Alltheemittedlaserphotonstravelinthesamedirection.(4).,populationinversionandgain(1)Interactionoflightwithmatter(2)SpontaneousEmission?Excitedatomsnormallyemitlightspontaneously?Photonsareuncorrelatedandindependent?IncoherentlightSpontaneousLifetime原子从激发态返回基态或较低能态,约10-7s(3)Stimulatedemission(,1916)Onephotoninandtwoout—AmplificationofLight?Excitedatomscanbestimulatedintoduplicatingpassinglight?Photonsarecorrelatedandidentical?Coherentlight?Anincidentphotonstrikesanatomandvibratestheatominphasewithit,:?isinphasewiththeincidentphoton.?hasthesamewavelengthastheincidentphoton.?hasthesamepolarizationastheincidentphoton.?travelsinsamedirectionasincidentphoton.(4)Essentialingredientsofalaserlightamplification+positiveopticalfeedback?Lightamplificationisachievedbystimulatedemission.?Theamplificationofthemediumisdefinedbythegaincoefficient,whichisdefinedbythefollowingequation:,:round-tripgain=round-triploss?ountthefactthatthelightpassestwicethrought
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