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Journal of Physics B Atomic Molecular and Optical Physics

Stochastic effects of the solvent on the absorptive and dispersive processes in a two-level system up to first order in the external field

Pedro J. Colmenares, Rafael Almeida, José Luis Paz

Published Oct 14, 1995• 25 citations
Publisher

Abstract

We have considered the stochastic effect of a thermal reservoir on a two-level system interacting with a classical electromagnetic field. The collective effect of the bath is modelled in this work as a random Bohr frequency whose manifestation is the broadening of the upper level according to a prescribed random function. This assumption transforms the optical Bloch equations to a system of multiplicative stochastic differential equations whose solution is found. After obtaining analytical expressions for the linear absorption coefficient and linear refraction index, numerical results are presented. This is done in the form of tridimensional plots of the optical properties as a function of the pump-frequency detuning factor and the strength or relaxation time of the noise source.

DOI
10.1088/0953-4075/28/19/021

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We have considered the stochastic effect of a thermal reservoir on a two-level system interacting with a classical electromagnetic field. The collective effect of the bath is modelled in this work as a random Bohr frequency whose manifestation is the broadening of the upper level according to a prescribed random function. This assumption transforms the optical Bloch equations to a system of multiplicative stochastic differential equations whose solution is found. After obtaining analytical expressions for the linear absorption coefficient and linear refraction index, numerical results are presented. This is done in the form of tridimensional plots of the optical properties as a function of the pump-frequency detuning factor and the strength or relaxation time of the noise source.
In this work, the thermal reservoir effects over the absorptive and dispersive nonlinear optical properties of a two-level molecular system in presence of classical electromagnetic fields, were modeled. The collective effects proper of the thermal reservoir are modeled as a time dependent frequency, whose manifestation is the broadening of the upper level according to a prescribed random function. Using the stochastic optical Bloch equations, analytical expression for the nonlinear induced susceptibilities and absorptive and dispersive optical properties, were obtained. Numerical calculations were carried out to construct surfaces corresponding to these optical properties as a function of the pump-probe frequency detuning, relationships between the longitudinal and transversal relaxation times, and molecular concentration of solute. Finally, we see an attenuation of these optical responses by the solvent effects and the high pump-intensity.
The optical properties of a two-level molecular system immersed in a thermal reservoir and irradiated by an electromagnetic field were studied using the optical stochastic Bloch equations. The effect of the solvent is modeled as a stochastical shift of the system's Bohr frequency and the electromagnetic field includes both pump and probe fields. The resulting analytical expressions were studied by means of two and three dimensional graphics of the optical properties as a function of the pump-frequency detuning factor and the strength of the noise source.
The stochastic effects of a thermal bath on a two-level molecular system interacting with a classical electromagnetic field are considered. The collective effects are modeled as a random Bohr frequency, whose manifestation is the broadening of the upper level according to a prescribed random function. A methodology based in cumulant expansions to obtain the average in the Fourier components associated with the coherence and populations, calculated by Optical Stochastic Bloch Equations (OSBE), is employed. The Four-wave mixing signal intensity as a function of the detuning of the pump beam, parametrized by the ratio of the relaxation times and other variables, is analyzed.
We calculate the non-linear absorptive and dispersive properties in four wave mixing (FWM) signal for a homogeneously broadened molecular two level system with dipole permanent moments interacting with two classical electromagnetic field,, using (omega) 1 equals (omega) 2, considering two sources of noise, the collective effect of the thermal bath, that is modeled as a random Bohr frequency and the effect of the electromagnetic field random amplitude. This assumptions transforms the optical Bloch equations to a system of multiplicative stochastic differential equations whose solution is found though an systematic treatment of cumulant expansion which lead directly to reduce OBE.
Absorptive and dispersive nonlinear optical properties have been studied considering a two-level molecular system with permanent dipole moments immersed in a thermal reservoir interacting with a classical electromagnetic field. Our model is based in a stochastic description, where the system–solvent interaction induces random shifts in the Bohr frequency (ω0) that transforms ω0 into a stochastic variable ξ(t). Our results show that it is necessary to neglect the rotating-wave approximation in order to measure the effect of the permanent dipole moments. The two-photon transitions over those with one-photon are favored when the permanent dipole moments are considered.