第四章 非线性激光光谱.pdf

第四章 非线性激光光谱(Nonlinear Laser Spectroscopy) §4.1 线性吸收和非线性吸收(Linear Absorption and Nonlinear Absorption) §4 .2 非均匀谱线的 饱和 Saturation of Inhomogenerous Line Profiles §4. 3. 偏振光谱 Polarization Spectroscopy §4 .4.多光子吸收光谱 Multiphoton Spectroscopy 第四章 非线性激光光谱(Nonlinear Laser Spectroscopy) single-mode lasers→ high resolution spectroscopy →overcome the limitation by Doppler broadening →several techniques based on selective saturation of atomic or molecular transitions by sufficiently intense lasers. The population density of molecule in the absorbing level is decreased by optical pumping →nonlinear dependence of the absorbed radiation power on the incident power, →nonlinear spectroscopy, also includes methods based on the simultaneous ansorption of two or more photons during an atomic or molecular transition. §4.1 线性吸收和非线性吸收(Linear Absorption and Nonlinear Absorption) dN /dt=B ρ(N -N )-R N +C 1 12 v 2 1 1 1 1 dN /dt=B ρ(N -N )-R N +C 2 12 v 1 2 2 2 2 Under stationary conditions(dN/dt=0), The unsaturation population difference(ρ=0): △N0= △N(ρ=0)=N 0-N 0=(C R -C R )/(R R ) 2 1 2 1 1 2 1 2 The saturation population difference(ρ≠0) 0 0 △N= △N /[1+B ρ(1/R +1/R )]= △N / (1+S) 12 v 1 2 S:saturation parameter S= B ρ /R*=B I /(R*.c),R*=R R /(R +R ) 12 v 12 v 1 2 1 2 Level diagram of an open two-level system with open relaxation channels into other levels and population paths from outside the system The power decrease of the incident