新专题3-能级与能级系统.pptxVIP

;a. 原子物理回顾——核外电子排布与能级； b. 能级系统的定义——定性解释； c. 能级系统的判别——定量分析；;;玻尔模型;由量子力学得出的氢原子能级图;四个量子数 ;4.自旋量子数 ms ( 1/2 , -1/2 ) ;四个量子数小结;三. 简并　简并态;原子中核外电子的排布要遵守;原子能级的填充次序;; 对应于L= 0，1, 2, 3,…的各壳层 其原子态分别记做 S,P,D,F,G,H, 等 ;由电子组态组合原子态;Hund定则——原子态对应的能级位置;L-S合成J：J=L+S,L+S-1,L+S-2,…,L-S Er的原子态： L=6, S=3/2, 对应 J=15/2, J=13/2, J=11/2, J=9/2. 即4I15/2, 4I13/2, 4I11/2, 4I9/2 4个原子态. L=3, S=3/2, 对应 J=9/2, J=7/2, J=5/2, J=3/2.即4F9/2, 4F7/2, 4F5/2, 4F3/2 4个原子态 L=4, S=3/2, 对应 J=11/2, J=9/2, J=7/2, J=5/2.即4G11/2, 4G9/2 , 4G7/2 , 4G5/24个原子态 L=5, S=1/2, 对应 J=11/2, J=9/2.即2H11/2, 2H9/2, 2个原子态。 ;4I15/2, 4I13/2, 4I11/2, 4I9/2 4个原子态对应的S最大，L也最大。对于Er3+离子， 其电子组态为6s24f9 ，同科电子数大于闭壳层占有数的一半，因此具有最大J值的能级处在最低位置，故4I15/2为基态，之后依次向上为4I13/2, 4I11/2和4I9/2 。;;红宝石激光器——三能级系统;Quasi-Three-Level Systems A quasi-three-level laser medium is one with a kind of intermediate situation, where the lower laser level is so close to the ground state that an appreciable population in that level occurs in thermal equilibrium at the operating temperature. As a consequence, the unpumped gain medium causes some reabsorption loss at the laser wavelength, and transparency is reached only for some finite pump intensity. For higher pump intensities, there is gain, as required for laser operation. Examples of quasi-three-level media are all ytterbium-doped gain media (e.g. Yb:YAG, or Yb:glass as used in optical fibers), neodymium-doped media operated on the ground state transition (e.g. 946 nm for Nd:YAG), thulium-doped crystals and glasses for 2-μm emission, and erbium-doped media for 1.5 or 1.6-μm emission, such as erbium-doped fiber amplifiers. ;An important fact is that the spectral shape of the optical gain in a quasi-three-level laser medium depends on the excitation level, because this affects the balance between emission and reabsorption. As a consequence, the laser wavelength obtained may depend on the resonator losses: high losses require a higher gain, and thus a higher excitation level, and consequently a shorter wavele