Atomic absorption spectra of the He I plasma in the static magnetic field in the absence of laser radiation are different from spectra in the presence of laser radiation. Especially, it has been theoretically predicted that the spectral shift of the satellite line, which is seen in the latter case, does not exist in the former case. In this paper, the effect of three-dimensional high-frequency electric fields on the σ+, σ−, and π components of the allowed 1 1S0-3 1P1 transition and the forbidden 1 1S0-3 1D2 lines in atomic absorption spectra of the He I plasma in a static magnetic field in the absence of a laser beam is investigated from the coupled equations for the probability amplitudes of atomic states. It is shown that they should give rise to a spectral shift of the allowed lines and satellites about forbidden lines. The calculation reveals that the shift is proportional to the mean-square stochastic electric field, and that the ratio of the intensity of the near satellite to that of the far satellite is different from the ratio obtained by the second-order perturbation theory or the three-level rotating-wave approximation. Discussion is given for the validity of this theory.
We have observed several different satellite transitions among HeI excited states. These satellites were induced by large, near-resonant, spatially inhomogeneous electric fields. A simple theory was proposed to explain the line shape of both the satellite and the allowed line based on the rotating-wave approximation. The plasma was contained in a dielectric waveguide and the laser mode pattern inside the guide was calculated and incorporated into the line-shape function. It was shown that excellent agreement between theory and experiment could be obtained over a wide range of experimental parameters. Agreement was very good in regimes where perturbation theory fails. We also observed that at high field strengths the Stark shift of the allowed component was less than the three-level theory predicted. We attribute this error to the fact that we have ignored all of the remaining levels of the HeI system.
Satellite lines emitted by a three-level atomic model in the presence of longitudinal electrostatic plasma waves and a non-resonant laser radiation field are investigated by calculating the autocorrelation function of the emitted light wave up to fourth order in the perturbation energy of the atomic system. Both the plasma wave and the radiation fields lead to a shift of the second-order Baranger and Mozer (1961) plasma satellites and of the allowed line. The intensities of the plasma satellites are enhanced by the laser radiation field. Under certain frequency conditions satellites pertaining to the radiation field appear in absorption. The same phenomenon occurs for the plasma satellites when the atoms are subjected to a single-mode plasma wave field.
The spectral line shape of the four-wave mixing (FWM) signal, induced by broad bandwidth laser fields, is derived in the case of a nonresonant interaction. The laser fields are assumed to have a Lorentzian spectrum arising from Markovian stochastic fluctuations described by the phase-diffusion, chaotic field, and Gaussian-amplitude models. The usual ``phase conjugating'' geometry for FWM is considered where the nonresonant interaction is determined only by the statistics of, and the correlations between, the pump and probe fields. For each one of the four possible correlation states between the three input fields and for each of the three fluctuating field models, the line shape of the FWM signal is calculated and shown to be particularly sensitive to the field statistics.
We reconsider the problem of a two-level system interacting with a radiation field in order to study some new features suggested by the actual experimental conditions. Pulse shape and duration effects are included in the formalism and the counter-rotating terms are retained. The criterion of validity of the rotating wave approximation (RWA) for pulsed fields is investigated; generalizing results well known in RWA, we establish some new formal results, including non-RWA contributions to all orders and for any pulse shape. The analysis is then carried out for fluctuating fields, by developing a method based on the theory of multiplicative stochastic differential equations. For short pulses, the non-Markovian character of the stochastic field parameters is expected to affect the process and, for broadband fields, the RWA has to be checked ab initio. Thus, a formalism is proposed which allows the study of both features. A wide range of numerical calculations are presented, clarifying the role of both intensity fluctuations and spectrum bandwidth in the case of a chaotic field, as well as their interplay with the pulse features.
The present paper treats the electromagnetically induced transparency (EIT), i.e., the absorption spectrum of a weak probe field, near-resonant to a material transition, in the presence of a strong amplitude-phase fluctuating field which couples the upper level of the transition to another excited level. The coupling field is assumed to be chaotic (i.e., a complex Gaussian process with a Lorentzian spectrum) and so strong that the material relaxation and the detuning can be neglected. In addition, we consider the Fourier transform of the spectrum
Uaa(t), which determines absorption of a probe field with a time-dependent intensity. The quantity
Uaa(t) equals a diagonal element of the average reduced evolution operator of the two-level system (TLS), coupled by the strong field. As a starting point, we use the stationary, partially averaged stochastic Schr\"odinger equation, which has the form of a set of two second-order differential equations. The theory is developed by combining analytical and numerical approaches. For the most important regime, when the rms Rabi frequency
V0 is much greater than the coupling-field bandwidth $\ensuremath{\nu},$ we obtain scaling relations for the EIT line shape and the TLS evolution. In particular, the absorption at the minimum (i.e., at the resonance frequency) scales as ${\ensuremath{\nu}}^{1/3}{V}_{0}^{\ensuremath{-}4/3},$ whereas the evolution function
Uaa(t) performs damped oscillations with the decay rate on the order of ${(V}_{0}^{2}\ensuremath{\nu}{)}^{1/3}.$ These results differ significantly from those following from the uncorrelated-jump model. The results of this paper are shown to be applicable to more general models of amplitude-phase fluctuations than the Gaussian-Markovian chaotic field.