粒子数反转.ppt

(Populationinversion)(whatisthepopulationinversion)第八章现代光学(ModernOptics)子,称为光放大。体积Sdz中进去时一个光子,(Populationinversion)(whatisthepopulationinversion)第八章现代光学(ModernOptics)单位时间单位体积内原子体系吸收的光能量:受激辐射产生的光能量:净生光能量可表示为:(Populationinversion)(whatisthepopulationinversion)第八章现代光学(ModernOptics)设为光强,,(c为光速)有令解得:(Populationinversion)(whatisthepopulationinversion)第八章现代光学(ModernOptics)n2>n1,时,,光强将按指数增强。n2<n1时,,光强将按指数衰减。通常情况下,n2总是小于n1,总是负的,吸收大于受激辐射。在特殊情况下,n2大于n1,为正的,称为粒子数反转。这时受激辐射大于吸收。(Populationinversion)(Two-levelenergysystem)第八章现代光学(ModernOptics)不断抽运使处于B12=B21=B ,w12=w21=w能否造成n2>n1?基态E1的原子激发到激发态E2,(Populationinversion)(Two-levelenergysystem)第八章现代光学(ModernOptics)图中A21为E2向E1的自发辐射系数,即自发辐射速率,有达到稳定时, 。故n2/n1=w/(A21+w)n2总是小于n1,所以,二能级系统物质不能实现粒子数反转。(Populationinversion)(Three-levelenergysystem)第八章现代光学(ModernOptics)(Populationinversion)(Three-levelenergysystem)第八章现代光学(ModernOptics)能级E3和E2上的粒子数变化率方程为:(Populationinversion)(Three-levelenergysystem)第八章现代光学(ModernOptics)达到稳定时,上二式等于0,有n3=(wn1+w23n2)/(A31+A32)在A32>>A31,w>>w12时,有n2/n1=w/A21外界抽运速度足够大时,有可能使w>A21,转。从而使n2>n1,(Populationinversion)(Three-levelenergysystem)第八章现代光学(ModernOptics)在三能级系统实现粒子数反转时,上能级是亚稳态能级E2,下能级是基态能级E1。由于基态能级上总是聚集着大量的粒子,因此,要实现粒子数反转,外界抽运要相当强。这是三能级系统的缺点。譬绊腑食袒用座孵哈号孤软肋泥趣畜嗜壮蚊尚瘪掇蚁跺锄拖典哟貌涝三沁粒子数反转粒子数反转