第二讲 经典传播.pptVIP

* 课程内容 绪论 经典传播 带间吸收和发光 自由电子、激子、分子材料 发光中心 发光材料的若干应用 * Classical propagation Propagation of light in a dense optical medium The dipole oscillator model Dispersion * The classical theory of optical propagation: Light : electromagnetic waves Atoms or molecules : classical dipole oscillators. A good general overview of the optical properties: Frequency dependence of the absorption coefficient Dispersion phenomenon （色散现象） Birefringence （双折射） * Propagation of light in a dense optical medium The classical propagation model was developed at the end of the nineteenth century following Maxwells theory of electromagnetic waves and the introduction of the concept of the dipole oscillator. Three types of oscillators in a medium: bound electrons (within a atom) vibrational oscillators free electron oscillators (metal) * Atomic oscillators Lorentz, 1878 Open circles: electrons (m0) Black circle: nucleus (mN) Spring: representing the restoring force (Ks) Reduced mass: Natural resonant frequency: Surposing there are several dipoles within every atom, to account for the fact that a given atom has many transition frequencies. the frequencies occur in the near-infrared, visible and ultraviolet spectral regions (1014-1015 Hz). * The electric dipole moment is defined as: For the oscillations of the atomic dipole, the heavy nucleus remain stationary, x(t) is the time varying displacement of the electron from its equilibrium position. A time varying dipole: The atom interacts with an external electromagnetic wave at frequency ?: If ? = ?0, resonant absorption; re-radiated photon, luminescence; radiationless transition. If ? ? ?0, non-resonant, transparent. The oscillators follow the driving wave, but re-radiate with a phase lag. The phase lag accumulates through the medium and retards the propagation of the wave front, leading to smaller velocity than in free space (v =c / n). ------ the origin of n * Vibrat