In a helium glow discharge, the A. C. Stark shift of the 4 3S 1 → 2 3P0,1,2 transition (λ ≅ 4 713 Å) induced by nonresonant interaction of the 4 3S and 4 3P levels with a multimode CO2 laser field is measured as a function of laser intensity in the range IL < 35 MW/cm 2. Departure from the linear intensity dependence given by second order perturbation theory is observed for IL > 2 MW/cm2. A three-level atom model taking into account the interaction with the laser field in a non perturbative way agrees with the experiment. Strong broadening is also detected for IL > 1 MW/cm2. This broadening grows with IL until a quasi-continuum spreading over 50 Å is observed for IL = 33 MW/cm2. This broadening results from amplitude and phase fluctuations of the laser field modes during interaction. For IL = 33 MW/cm2 the recorded 4 713 Å spectral line shape reflects the statistical distribution of the mode amplitudes.
In a helium glow discharge, the A. C. Stark shift of the 4 3S 1 → 2 3P0,1,2 transition (λ ≅ 4 713 Å) induced by nonresonant interaction of the 4 3S and 4 3P levels with a multimode CO2 laser field is measured as a function of laser intensity in the range IL < 35 MW/cm 2. Departure from the linear intensity dependence given by second order perturbation theory is observed for IL > 2 MW/cm2. A three-level atom model taking into account the interaction with the laser field in a non perturbative way agrees with the experiment. Strong broadening is also detected for IL > 1 MW/cm2. This broadening grows with IL until a quasi-continuum spreading over 50 Å is observed for IL = 33 MW/cm2. This broadening results from amplitude and phase fluctuations of the laser field modes during interaction. For IL = 33 MW/cm2 the recorded 4 713 Å spectral line shape reflects the statistical distribution of the mode amplitudes.
The enhancement of the electron collisional broadening of the 4s 3 S 1 and 4p 3 P 2,1,0 degrees levels in a helium glow discharge (n e =10 13 -10 14 cm -3 ), induced by the non-resonant interaction of the 4s 3 S 1 and 4p 3 P 2,1,0 degrees levels with a CO 2 laser field, is reported. This extra broadening depends on the product of the electron density with the laser field amplitude and manifests itself on the 4713 and 3188 AA linewidths (the transitions 4s 3 S 1 to 2p 3 P 2,1,0 degrees and 4p 3 P 2,1,0 degrees to 2s 3 S 1 respectively). This effect results from the destruction, by electronic collisions, of the coherence induced by the laser field between the 4s 3 S 1 and 4p 3 P 2,1,0 degrees levels, and can be viewed as an electron-atom collisional fluorescence redistribution process at relatively large laser detuning.
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.
A theory of ac Stark splitting at double resonance in a three-level system is presented, the upper and lower transitions being coupled to a near-resonant intense multimode field and a weak monochromatic field, respectively. Linear response to a weak field is considered. The analytical treatment calling into action a diagram technique and the quasistationary-states method is carried out beyond the limits of perturbation theory and the nonresonant approximation. The multimode structure of the radiation spectrum results in a quasi-periodicity of the field-correlation function. It leads to a strong modulation of the absorbtion line shape with a period $\frac{1}{2}\ensuremath{\Delta}{\ensuremath{\nu}}_{0}$ where $\ensuremath{\Delta}{\ensuremath{\nu}}_{0}$ is the intermode interval. The role of different weakening effects such as spontaneous decay of the levels, the finite pulse duration, and instrumental and natural fluctuations of a single mode is studied. The last effect is shown to be the most important, and a possible method of direct measurement of the natural-fluctuations' correlation function is proposed.
The prediction of the energy level shifts and intensity transfer in atomic hydrogen and helium spectra caused by an external electric field was one of the first applications of wave mechanics. Early measurements relied on electrical discharge sources for excited atoms; since discharge processes will not produce excited states with n > 7 in observable densities, very large (10s to 100s kV cm) electric fields were required to resolve spectral modifications. The development of high peak power lasers enabled excitation to high n (Rydberg) states, increasing field sensitivity down to millivolts/cm and allowing comparison of experiment and theory in well-defined conditions. Field modified selection rules can be used to measure the field direction as well as magnitude. Analysis of line shape simulations of Stark modified Rydberg spectra reveals pitfalls in commonly used field measurement techniques. An ambiguity in defining series termination results in a factor of 2 discrepancy in field measurements based on Inglis Teller line merging. Field-induced line broadening (unresolved manifold splitting) in triplet and singlet helium are shown to differ significantly, with triplet broadening nonlinear with field.
The ac Stark shift (or light shift) of the $6{\phantom{\rule{0.16em}{0ex}}}^{2}{S}_{1/2}(F=3\ensuremath{\leftrightarrow}4)$ transition in 133Cs, as observed through coherent population trapping under pulsed excitation, is measured using a 133Cs gas cell and the D1-line vertical-cavity surface-emitting laser. This light shift can be calculated using density-matrix analysis. We derive an expression for this shift as a function of light intensity, showing that it varies linearly with respect to light intensity only with intensities higher than 1.0 mW/cm2. For pulsed excitation of high laser intensity, the variation in light shift is 20 times lower than that when using a continuous wave. The differences between the results of theory and experiment are discussed, taking into account the difference in conditions assumed; the results from theoretical analysis, taking the attenuation of the first-order sideband into account, approximately agree with the experimental results. The light shift is reduced by shortening the observation times.
We have investigated the ac Stark shift of a two-photon transition induced by a model stochastic field by using a Monte Carlo technique. The model field has a stochastic single mode, which can possess both colored amplitude and colored frequency fluctuations. The stochastic field’s modification of the ac Stark shift is quantified by a parameter M, which is the ratio of the Stark shift in the model stochastic field to the Stark shift that would be obtained in a phase-diffusion field of equivalent linewidth (i.e., a field with frequency fluctuations but no amplitude fluctuations). In the regime of weak fields, below saturation of the bound-bound transition, we find that M is greater than unity: the Stark shift is enhanced by the stochastic field. Moreover, in this regime M is an increasing function of the field’s degree of photon bunching. In strong fields, where the bound–bound transition is nearly saturated, the enhancement of the Stark shift is diminished, so much so that in extremely strong fields M is actually less than unity. Our calculations indicate that the ac Stark shift’s modification occurs through two distinct processes, depending on the strength of the field. In weak fields enhancement of a multiphoton transition’s Stark shift is influenced primarily by the intrinsic correlation between ac-Stark-shift fluctuations and Rabi-frequency fluctuations. In strong fields the fluctuating Stark shifts give rise to an asymmetric resonance line shape in a fashion analogous to inhomogeneous broadening. The line shape’s peak position then has a sublinear dependence on the stochastic field’s intensity, and this yields a diminished value of M.