Cancellation of laser phase fluctuations in Stokes and anti-Stokes generation

Abstract

In the coherent anti-Stokes Raman scattering process, the spectrum of the generated optical phonon depends on the degree of temporal correlation between the pump laser field and the Stokes field. When the two fields are strongly correlated, such as when the Stokes field is generated with stimulated Raman scattering (SRS), the spectral shape of the optical phonon is found experimentally and theoretically to be the same as the gain-narrowed Raman line shape because the laser phase fluctuations cancel out totally, leaving only the collisional noise in the SRS process. When the two fields are uncorrelated, the shape of the optical-phonon spectrum is found to be the same as the Raman line shape without gain narrowing. When two fields are partially correlated, then the two spectral components appear together. We provide a method to measure the degree of correlation between two optical fields that have different central frequencies. The theory developed to interpret the experimental results is an extension of the quantum theory of SRS to include anti-Stokes scattering. We show that only in the high-gain limit can the quantum fluctuations be thought of as arising from a classical noise process.

Quantum-statistical theory of Raman scattering processes

“…on insertion of Eqs. ( 149), (143), and ( 145) into (43). With regard to the relation (46), the minimal variance for the field, (∆ XL− ) 2 , is constant up to the second order in time:…”

“…It is quite remarkable that there exists a strict operator solution [134,135] of the master equation describing the evolution of the generalized Knight model, which describes the system of an atom undergoing Raman transitions between two degenerate levels on interaction with a quantized field in a lossy cavity driven by an external field including the effects of atomic dephasing collisions. An extension of the propagation theory of Ra-man effect [140,141] to include anti-Stokes scattering has been developed by Kilin [142] and independently by Li et al [143]. As mentioned, we shall analyze another model of the Stokes-anti-Stokes coupling within the framework of the temporal theory of Raman effect proposed by Walls [122] and extensively studied by Peřina and coworkers (see Refs.…”

“…The standing-wave theory of Raman scattering properly describes the macroscopic fluctuations in the low-gain and high-gain regime (see Refs. [22,23,143] and references therein). In the latter limit the quantum fluctuations of the generated fields can be thought of as arising from a classical noise process, contrary to the low-gain limit, where certain nonclassical effects occur.…”