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Acta Optica Sinica

Atomic velocity-changing collisions in polarization intermodulated excitation spectroscopy

Ang Z

Published Jan 1, 1982• 0 citations
OpenAlex

Abstract

Polarization intermodulated excitation (POLINEX) spectroscopy is a new developing Doppler-free spectroscopic technique which combines the advantages of the polarization spectroscopy and the intermodulated fluorescence speotroscopy. In this technique, a tunable laser beam is circular polarized first and then divided into two parts of nearly same intensities. Two rotating polarizers of different modulated frequencies are used to change the directions of these linear polarized beams periodically with time. When they interact with the atoms, the fluorescence signal are detected via a lock-in amplifier. The POLINEX spectroscopy can effectively eliminate the Doppler-broadened pedestal due to the velocity-changing collisions among atoms as the polarization-modulation is used instead of the amplitude modulation. And that pedestal is a problem in the original saturated spectroscopy and the intermodulated fluorescence spectroscopy. Meanwhile, there is no asymmetry of the line-shape in the polarization spectroscopy, because only the fluorescent or opto-galvanic signal are detected in this new method. In this paper a study of velocity-changing collisions in POLINEX spectroscopy using the rate equation approach is presented. A kernel function is introduced to describe the probability of atom moving out or in the state V (velocity) and m (magnetic quantum number) and the related terms additional to the rate equations. We calculate the total absorption rate and pick out the term concerning the mutual absorption (intermodulated signal). The amplitude of signal is proportional to the difference of the absorption rate when the senses of polarization of two counter-propagating laser beams are same or perpendicular to each other. We obtain the results which show the term related with the Doppler-broadened pedestal being cancelled after the operation of Glebsch-Gordon coefficients. These results coincide with the experiments performed before. Using the density matrix approach we can obtain the same results.

Related papers

Atomic velocity-changing collisions in polarization excitation spectroscopyII

Ang Z

Polarization intermodulated excitation (POLINEX) spectroscopy is a new nonlinear high resolution speotroscopy. It combines polarization spectroscopy with intermodulated fluorescence speotroscopy. So the POLINEX spectrosoopy has some advantages of them. In author's former paper, we had used the rate equation approach to analyze how the Doppler background caused by atomic collisions was eliminated and how the Loren-tzian line shape was kept. In this paper, we use the semiolassioal theory of Lamb to analyze the POLINEX speotroscopy further more. This method is more reasonable. Considering laser beam's polarization, energy level's degeneracy and collision cross relaxation, by means of the equation of motion of density matrix, we have calculated the polarizability of the atomic system submitted to laser beams I1 and I2 to the third order x(3). Then, from x(3) we have evaluated nonlinear components of the absorption coefficient a. So we can obtain the strength and shape of the intermodulated signal in POLINEX spectroscopy. The conclusion is in conformity with the experimental results. Moreover, it predicts the pressure shift and pressure broadening which can't be predicted by the rate equation approach.

Acta Optica Sinica•Jan 1, 1982•0 citations

Phase orthogonality in polarization intermodulated excitation (POLINEX) spectroscopy

Guozheng Yan, Z Wang

This paper reports the phase orthogonality both theoreitically and experimentally in POLINEX spectroscopy with a modulated polarization and a fixed polarization of two linearly polarized optical beams. It is possible to make the phase of the Doppler-free signal orthogonal to that of the Doppler-broadened background, if the fixed polarizer is properly adjusted.

Acta Optica Sinica•Jan 1, 1983•0 citations

Comparison of absorption, fluorescence, and polarization spectroscopy of atomic rubidium

Seth Ashman, C. Stifler, Joaquín Romero

An ongoing spectroscopic investigation of atomic rubidium utilizes a two-photon, single-laser excitation process. Transitions accessible with our tunable laser include 5P1/2 (F ′ ) ← 5S1/2 (F) and 5P3/2 (F ′ ) ← 5S1/2 (F). The laser is split into a pump and probe beam to allow for Doppler-free measurements of transitions between hyperfine levels. The pump and probe beams are overlapped in a counter-propagating geometry and the laser frequency scans over a transition. Absorption, fluorescence and polarization spectroscopy techniques are applied to this basic experimental setup. The temperature of the vapor cell and the power of the pump and probe beams have been varied to explore line broadening effects and signal-to-noise of each technique. This humble setup will hopefully grow into a more robust experimental arrangement in which double resonance, two-laser excitations are used to explore hyperfine state changing collisions between rubidium atoms and noble gas atoms. Rb-noble gas collisions can transfer population between hyperfine levels, such as 5P3/2 (F ′ = 3) Collision ←− 5P3/2 (F ′ = 2), and the probe beam couples 7S1/2 (F ′′ = 2) ← 5P3/2 (F ′ = 3). Polarization spectroscopy signal depends on the rate of population transfer due to the collision as well as maintaining the orientation created by the pump laser. Fluorescence spectroscopy relies only on transfer of population due to the collision. Comparison of these techniques yields information regarding the change of the magnetic sublevels, mF , during hyperfine state changing collisions.

Bulletin of the American Physical Society•Jun 11, 2015•0 citations

Velocity-selective optical pumping and Doppler-free spectroscopy

M. Pinard, C.G. Aminoff, Franck Laloë

We describe a spectroscopic method combining saturated absorption and Zeeman optical pumping. A weak expanded monochromatic laser beam creates a velocity-correlated orientation in an atomic level without optical saturation. A polarization-modulated counterpropagating detection beam provides signals related to simple atomic observables. Combination with magnetic resonance techniques is described. We have applied this method to metastable states of Ne, with nuclear or electronic orientation. Effects of velocity-changing, depolarization (Kastler- or Dehmelt-type pumping) or metastability exchange collisions are discussed.

Physical Review A•Jun 1, 1979•78 citations

Theory of collision effects in Doppler-free spectroscopy

P. R. Berman

A theory of the influence of binary collisions on the line shapes associated with Doppler-free spectroscopy is presented. The specific calculation is for two-photon absorption through a real or virtual intermediate state, but the extension of the results to alternative level schemes is included. Collisions are treated quite generally at first, but, ultimately, a simple but reasonable collision model is adopted to properly account for both the "phase-interrupting" and "velocity-changing" aspects of collisions. It is shown that collisional processes can be used to distinguish between the "two-quantum" and "stepwise" contributions to the two-photon excitation rate. Moreover, it is demonstrated that systematic experimental line-shape investigations, in addition to providing tests of current collision theories, can lead to values for collision broadening and shift parameters, excitation transfer rates, magnetic substate relaxation rates, velocity-changing collision rates, and collision kernels. Consequently, Doppler-free spectroscopy can provide a new and important probe of collision effects in atomic and molecular systems.

Physical Review A•Jun 1, 1976•49 citations

Polarization spectroscopy using short-pulse lasers: Theoretical analysis

Sukesh Roy, Robert P. Lucht, Thomas A. Reichardt

The physics of short-pulse polarization spectroscopy (PS) and the diagnostic potential for quantitative measurements of species concentration are investigated by direct numerical integration (DNI) of the time-dependent density matrix equations for a multistate system. The effects of laser power, collision rates, and Doppler broadening on the short-pulse PS signal generation process are investigated by systematically varying these parameters in the numerical calculations. It is found that the use of a short-pulse laser (laser pulse width τL<characteristic collision time τC) significantly decreases the collision-rate dependence of the PS signal compared to the long-pulse laser case (τL>τC), even for a nonsaturating pump beam. For a saturating pump beam, the short-pulse PS signal is found to be nearly independent of collision rate. Increasing the collision rate by a factor of 100 (from 108 to 1010 s−1), the calculated PS signal strength decreases by only a factor of 2 for a 100-ps pump laser at high intensity. This insensitivity of the PS signal to the collision rate in the medium enhances greatly the potential for quantitative application of the technique for concentration measurements in reacting flows. The underlying physics of the short-pulse PS is explored by studying the effects of collision rate, Doppler broadening, and the pump laser intensity on the temporal profile of the Zeeman state populations and the coherences between the Zeeman states.

The Journal of Chemical Physics•Jan 8, 2002•21 citations
Polarization intermodulated excitation (POLINEX) spectroscopy is a new developing Doppler-free spectroscopic technique which combines the advantages of the polarization spectroscopy and the intermodulated fluorescence speotroscopy. In this technique, a tunable laser beam is circular polarized first and then divided into two parts of nearly same intensities. Two rotating polarizers of different modulated frequencies are used to change the directions of these linear polarized beams periodically with time. When they interact with the atoms, the fluorescence signal are detected via a lock-in amplifier. The POLINEX spectroscopy can effectively eliminate the Doppler-broadened pedestal due to the velocity-changing collisions among atoms as the polarization-modulation is used instead of the amplitude modulation. And that pedestal is a problem in the original saturated spectroscopy and the intermodulated fluorescence spectroscopy. Meanwhile, there is no asymmetry of the line-shape in the polarization spectroscopy, because only the fluorescent or opto-galvanic signal are detected in this new method. In this paper a study of velocity-changing collisions in POLINEX spectroscopy using the rate equation approach is presented. A kernel function is introduced to describe the probability of atom moving out or in the state V (velocity) and m (magnetic quantum number) and the related terms additional to the rate equations. We calculate the total absorption rate and pick out the term concerning the mutual absorption (intermodulated signal). The amplitude of signal is proportional to the difference of the absorption rate when the senses of polarization of two counter-propagating laser beams are same or perpendicular to each other. We obtain the results which show the term related with the Doppler-broadened pedestal being cancelled after the operation of Glebsch-Gordon coefficients. These results coincide with the experiments performed before. Using the density matrix approach we can obtain the same results.
Polarization intermodulated excitation (POLINEX) spectroscopy is a new nonlinear high resolution speotroscopy. It combines polarization spectroscopy with intermodulated fluorescence speotroscopy. So the POLINEX spectrosoopy has some advantages of them. In author's former paper, we had used the rate equation approach to analyze how the Doppler background caused by atomic collisions was eliminated and how the Loren-tzian line shape was kept. In this paper, we use the semiolassioal theory of Lamb to analyze the POLINEX speotroscopy further more. This method is more reasonable. Considering laser beam's polarization, energy level's degeneracy and collision cross relaxation, by means of the equation of motion of density matrix, we have calculated the polarizability of the atomic system submitted to laser beams I1 and I2 to the third order x(3). Then, from x(3) we have evaluated nonlinear components of the absorption coefficient a. So we can obtain the strength and shape of the intermodulated signal in POLINEX spectroscopy. The conclusion is in conformity with the experimental results. Moreover, it predicts the pressure shift and pressure broadening which can't be predicted by the rate equation approach.
An ongoing spectroscopic investigation of atomic rubidium utilizes a two-photon, single-laser excitation process. Transitions accessible with our tunable laser include 5P1/2 (F ′ ) ← 5S1/2 (F) and 5P3/2 (F ′ ) ← 5S1/2 (F). The laser is split into a pump and probe beam to allow for Doppler-free measurements of transitions between hyperfine levels. The pump and probe beams are overlapped in a counter-propagating geometry and the laser frequency scans over a transition. Absorption, fluorescence and polarization spectroscopy techniques are applied to this basic experimental setup. The temperature of the vapor cell and the power of the pump and probe beams have been varied to explore line broadening effects and signal-to-noise of each technique. This humble setup will hopefully grow into a more robust experimental arrangement in which double resonance, two-laser excitations are used to explore hyperfine state changing collisions between rubidium atoms and noble gas atoms. Rb-noble gas collisions can transfer population between hyperfine levels, such as 5P3/2 (F ′ = 3) Collision ←− 5P3/2 (F ′ = 2), and the probe beam couples 7S1/2 (F ′′ = 2) ← 5P3/2 (F ′ = 3). Polarization spectroscopy signal depends on the rate of population transfer due to the collision as well as maintaining the orientation created by the pump laser. Fluorescence spectroscopy relies only on transfer of population due to the collision. Comparison of these techniques yields information regarding the change of the magnetic sublevels, mF , during hyperfine state changing collisions.
We describe a spectroscopic method combining saturated absorption and Zeeman optical pumping. A weak expanded monochromatic laser beam creates a velocity-correlated orientation in an atomic level without optical saturation. A polarization-modulated counterpropagating detection beam provides signals related to simple atomic observables. Combination with magnetic resonance techniques is described. We have applied this method to metastable states of Ne, with nuclear or electronic orientation. Effects of velocity-changing, depolarization (Kastler- or Dehmelt-type pumping) or metastability exchange collisions are discussed.
A theory of the influence of binary collisions on the line shapes associated with Doppler-free spectroscopy is presented. The specific calculation is for two-photon absorption through a real or virtual intermediate state, but the extension of the results to alternative level schemes is included. Collisions are treated quite generally at first, but, ultimately, a simple but reasonable collision model is adopted to properly account for both the "phase-interrupting" and "velocity-changing" aspects of collisions. It is shown that collisional processes can be used to distinguish between the "two-quantum" and "stepwise" contributions to the two-photon excitation rate. Moreover, it is demonstrated that systematic experimental line-shape investigations, in addition to providing tests of current collision theories, can lead to values for collision broadening and shift parameters, excitation transfer rates, magnetic substate relaxation rates, velocity-changing collision rates, and collision kernels. Consequently, Doppler-free spectroscopy can provide a new and important probe of collision effects in atomic and molecular systems.
The physics of short-pulse polarization spectroscopy (PS) and the diagnostic potential for quantitative measurements of species concentration are investigated by direct numerical integration (DNI) of the time-dependent density matrix equations for a multistate system. The effects of laser power, collision rates, and Doppler broadening on the short-pulse PS signal generation process are investigated by systematically varying these parameters in the numerical calculations. It is found that the use of a short-pulse laser (laser pulse width τL<characteristic collision time τC) significantly decreases the collision-rate dependence of the PS signal compared to the long-pulse laser case (τL>τC), even for a nonsaturating pump beam. For a saturating pump beam, the short-pulse PS signal is found to be nearly independent of collision rate. Increasing the collision rate by a factor of 100 (from 108 to 1010 s−1), the calculated PS signal strength decreases by only a factor of 2 for a 100-ps pump laser at high intensity. This insensitivity of the PS signal to the collision rate in the medium enhances greatly the potential for quantitative application of the technique for concentration measurements in reacting flows. The underlying physics of the short-pulse PS is explored by studying the effects of collision rate, Doppler broadening, and the pump laser intensity on the temporal profile of the Zeeman state populations and the coherences between the Zeeman states.