It is shown that the feedback arising from the Rayleigh scattering leads to an absolute instability of the stimulated Raman effect. The conditions for the occurrence of this instability are determined and it is shown that the distributed feedback due to the Rayleigh scattering differs from the feedback in a resonator.
This paper reviews the main experimental and theoretical developments in stimulated Raman scattering of light, which has been actively investigated since 1962. The effect cannot be discussed properly without paying attention to related nonlinear effects which include stimulated Brillouin and Rayleigh scattering, self-focusing of light, and modulation of the refractive index. The physical processes are emphasized and no encyclopedic survey of all the data and the research literature is attempted, but a brief historical account is added in the final section.
Polarization effects in stimulated Raman and stimulated Rayleigh scattering and self focusing are investigated from the viewpoint of the scattering of polarized photons by molecules. Both stimulated vibrational Raman scattering in liquids and stimulated rotational Raman scattering in gases are considered, and it is demonstrated that the polarization changes and relative power thresholds for different laser polarizations should be somewhat different to those predicted in other theories. For example, the ellipticity eta 0 of the stimulated rotational Raman photons in the forward direction from Delta J=+or-2 transitions in gaseous symmetric top molecules is given in terms of the initial ellipticity eta 1 by sin 2 eta 0 = - 5 / 7 sin 2 eta 1 , whereas conventional theories predict that eta 0 and eta 1 are equal in magnitude and opposite in sign. Furthermore it is shown that deviations from this relation could provide a measure of the degree of optical orientation of the molecules.
A study is made of the problem of stimulated Raman scattering (STRS) in a resonant medium pumped by a strong pulse satisfying the adiabaticity condition. It is shown that in the absence of relaxation the maximum STRS gain is reached during the tail (trailing edge) of the pump pulse, which is the reason for the absence of the Stark shift. If the pump pulse is considerably longer than the relaxation time, the lag of the STRS pulse behind the pump pulse is short and then the Stark shift is manifested in the spectrum and a characteristic interference structure is formed. Noise and monochromatic "seeding" variants are considered.
An analysis is made of some features of spontaneous resonance Raman scattering representing a noise signal which is amplified by a strong field in a nonlinear medium. A detailed review is made of the experimental results obtained in investigations of the spectra of stimulated preresonance and resonance Raman scattering in nonlasing and lasing systems. It is shown that, depending on the experimental conditions, these spectra may be due to transitions between vibrational levels of molecules which are in the ground or first excited electronic states. The example of several compounds is used to demonstrate the information which can be derived from such spectra. Possible practical applications of studies of such spectra are indicated. The physical basis of the theory of stimulated resonance Raman scattering is discussed and conclusions are drawn on the nature and mechanism of this Raman effect.
We present a study of pump-probe spectroscopy experiments in an optical lattice. The probe transmission spectrum contains three types of resonances similar to those found in usual nonlinear media: Raman, Brillouin and Rayleigh resonances. We show evidence of the existence of a propagating elementary excitation in the lattice which involves no interaction between the particles and lead to a Brillouin-like scattering. We discuss the central Rayleigh resonance and show that its shape is sensitive to the radiation pressure.