1. In classical mechanics a purely harmonic oscillator responds purely linearly to an external force. Only those quantum mechanical systems with exactly equally spaced energy levels, infinite in number, have this property. We will discuss only models of molecules characterized by a finite number of energy levels. Our entire discussion thus necessarily deals with nonlinear molecular oscillators
2. Optical Resonance and Two-Level Atoms;Allen,1975
3. Self-Induced Transparency
4. Elements of Soliton Theory;Lamb,1980
5. Analytical Descriptions of Ultrashort Optical Pulse Propagation in a Resonant Medium