The stimulated radiation and absorption theory of light based on low order linear interaction is considered symmetrical in time reversal processes at present. It is provided in the paper that after high order nonlinear interaction between radiation fields and charged particles is considered, time reversal symmetry in the stimulated radiation and absorption processes would be violated. Based on revised theory, the non-equilibrium and nonlinear phenomena just as generation of laser, amplification of non-population inversion, self-induced transparency and self-induced absorption can be explained more rationally. Other nonlinear processes light such as multiple frequency, sum frequency and difference frequency, double stationary state, self-focusing and self-defocusing, double and multi-photon absorption, stimulated Raman and Brillouim scatterings, photon echo and so on are also enumerated and analyzed in the paper. The results show that most processes of nonlinear optics are violated time reversal symmetry obviously.
Abstract A review of the theory of the stimulated resonance Raman scattering (SRRS) is given. The calculation of the gains for the SRRS with the ground level (SRRS I) or an excited one (SRRS II) as initial states shows that there are some restrictions for their appearance. Due to the strong resonance absorption of the pumping wave and the disturbing influence of stimulated fluorescence the SRRS I is not observable in a Franck‐Condon excitation and in an absorption of Lorentzian line shape. The SRRS II has a sufficiently large gain on the condition τel ≪vib (τel, τvib – transversal relaxation time of the electronic or vibronic transition). In case of a strong deviation of the wings of the absorption profile from the Lorentzian shape, however, the SRRS I is favoured rather than the two other processes. Another possibility to avoid the resonance absorption of the pumping wave exists for the transversal excitation of the SRRS. Thereby the limit of application of the SRRS may be extended to other substances which are no saturable absorbers. Apart from the saturable absorption and the transversal excitation the self‐induced transparency is the third possibility to generate SRRS of ultrashort light pulses.
We theoretically investigate a scheme in which stimulated Raman scattering (SRS) can be suppressed by coherently controlling the coupling between molecular states. In conventional SRS, two laser beams at different frequencies interact resonantly with molecular vibration to induce a gain and a loss for the two beams, respectively. In our scheme, a third beam is introduced to couple the vibrational state to another coupling state. As a result, SRS is suppressed in a way analogous to electromagnetically induced transparency. We calculated the SRS signal analytically by the density matrix approach, and investigated the feasibility of this scheme for real molecular imaging. In SRS microscopy, a donut-shaped coupling laser can be used to suppress the SRS signal from the rim part of the focal spot, leading to super-resolution. Based on our numerical studies, the lateral resolution starts to be enhanced when the coupling laser intensity exceeds
0.1TW/cm2 at picosecond pulse duration.