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AIAA AVIATION Forum

Coherent Control of Xe-136 within the Atomic Collision Window

Amirhossein Abbasszadehrad, Arthur Dogariu, Richard B. Miles

Published Jul 16, 2025• 1 citation
Publisher

Abstract

Two-photon absorption of a circularly polarized UV beam of a femtosecond laser at 256 nm is used to pump ground state electrons of Xe-136 to the m = +2 or m = -2 sublevels of the 6p [5/2]2 excited state depending on the handedness of the circular polarization. A copropagating circularly polarized IR beam of a CW laser at 788.134 nm is used to further excite these electrons to the 8s [3/2]2 state through a single photon absorption process. The absorption of the IR beam is measured by a fast detector. In theory, the same and the opposite handedness of the circular polarization of the two beams respectively result in a forbidden and an allowed final transition, hence zero and finite absorption of IR photons, respectively. In practice, finite absorption is observed in both cases. However, the absorption signal in the forbidden case is less intense and delayed by about 70 ps relative to the absorption in the allowed case. This time delay is a measure of the depolarization rate at which exited electrons in m = +/-2 sublevels move to other sublevels, namely, m = +/-1 and m = 0 making the final transition possible, resulting in the delayed absorption of IR photons.

DOI
10.2514/6.2025-3745

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The Journal of Chemical Physics•Mar 3, 2017•1 citation
Two-photon absorption of a circularly polarized UV beam of a femtosecond laser at 256 nm is used to pump ground state electrons of Xe-136 to the m = +2 or m = -2 sublevels of the 6p [5/2]2 excited state depending on the handedness of the circular polarization. A copropagating circularly polarized IR beam of a CW laser at 788.134 nm is used to further excite these electrons to the 8s [3/2]2 state through a single photon absorption process. The absorption of the IR beam is measured by a fast detector. In theory, the same and the opposite handedness of the circular polarization of the two beams respectively result in a forbidden and an allowed final transition, hence zero and finite absorption of IR photons, respectively. In practice, finite absorption is observed in both cases. However, the absorption signal in the forbidden case is less intense and delayed by about 70 ps relative to the absorption in the allowed case. This time delay is a measure of the depolarization rate at which exited electrons in m = +/-2 sublevels move to other sublevels, namely, m = +/-1 and m = 0 making the final transition possible, resulting in the delayed absorption of IR photons.
The two-photon absorption of a linearly or circularly polarized UV beam of a femtosecond laser at 256 nm is used to pump ground-state electrons of Xe-129 and Xe-136 to sublevels of the 6p [5/2] 2 excited state depending on the polarization. A copropagating linearly or circularly polarized IR beam of a picosecond laser at near 788.132 nm is used to further excite these electrons to the 8s [3/2]° 2 state through a single photon absorption process. The absorption of the IR beam is measured by a fast detector. The type and handedness of polarization of the two beams result in different absorption of IR in the final transition. The effect of applying an external magnetic field on the absorption of the IR beam is studied.
Competitive inhibition of a resonance enhanced multiphoton ionization process by a resonant four-wave mixing has been observed in Xe atoms. When an intense IR (1064 nm) laser was applied to a sample of Xe which was also being irradiated by a UV laser tuned to the two-photon absorption line of Xe, the two-photon-resonant three-photon ionization signals decreased with increasing IR laser power. This phenomenon is dependent on the resonant states of Xe and the polarization of the two laser beams. Three 6sss excited states [5/2]2{}_{2}2​, [3/2]2{}_{2}2​, and [1/2]0{}_{0}0​ were examined. At the [1/2]0{}_{0}0​ resonant state, the ion signals were not decreased but slightly increased with the increase of the IR laser power. No suppression of the ion signal was observed at the [5/2]2{}_{2}2​ resonant state, when the polarization directions of the lasers were perpendicular to each other. The result of the polarization dependence reflects the selection rules of four-wave mixing. A simple rate equation analysis including the contribution of two-photon ionization from the [1/2]0{}_{0}0​ state by the IR laser well represents the IR laser-power dependence of the ion signal.
Utilizing two-photon excitation in hot Rb vapor we demonstrate the generation of collimated optical fields at 420 and 1324 nm. Input laser beams at 780 and 776 nm enter a heated Rb vapor cell collinear and circularly polarized, driving Rb atoms to the 5D5/2 state. Under phase-matching conditions coherence among the 5S1/2 → 5P3/2 → 5D5/2 → 6P3/2 transitions produces a blue (420 nm) beam by four-wave mixing. We also observe a forward and backward propagating IR (1324 nm) beam, due to cascading decays through the 6S1/2 → 5P1/2 states. Power saturation of the generated beams is investigated by scaling the input powers to greater than 200 mW, resulting in a coherent blue beam of 9.1 mWpower, almost an order of magnitude larger than previously achieved. We measure the dependences of both beams in relation to the Rb density, the frequency detuning between Rb ground-state hyperfine levels, and the input laser intensities. (C) 2014 Optical Society of America
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.
Abstract We theoretically and experimentally demonstrate the control of the intermediate state absorption in an ( n + m ) resonance-mediated multi-photon absorption process by the polarization-modulated femtosecond laser pulse. An analytical solution of the intermediate state absorption in a resonance-mediated multi-photon absorption process is obtained based on the time-dependent perturbation theory. Our theoretical results show that the control efficiency of the intermediate state absorption by the polarization modulation is independent of the laser intensity when the transition from the intermediate state to the final state is coupled by the single-photon absorption, but will be affected by the laser intensity when this transition is coupled by the non-resonant multi-photon absorption. These theoretical results are experimentally confirmed via a two-photon fluorescence control in (2 + 1) resonance-mediated three-photon absorption of Coumarin 480 dye and a single-photon fluorescence control in (1 + 2) resonance-mediated three-photon absorption of IR 125 dye.
Stimulated emission (SE) induced by pulsed two-photon excitation of the 6p′[1/2]0, 6p′[3/2]2, 7p[1/2]0, 7p[3/2]2, and 7p[5/2]2 states of the Xe atom has been studied. Spectra of SE were recorded in the 800–3500 nm region, which covers the 6p′, 7p → 7s (2500–3500 nm), 6p′, 7p → 5d (1000–2000 nm), 7s → 6p (1200–1900 nm) transitions, as well as the near-IR 6p → 6s (800–1000 nm) transitions. It is shown that excitation of the 7p states results in radiative cascade via the 7s states, 7p → 7s → 6p, although at least one case of cascading via the 5d states is also observed. Spectra of SE induced by excitation of the 6p′ states are dominated by the 6p′ → 6s′ transitions in the near IR and the 6p′ → 5d[1/2]1 → 6p[1/2]1 → 6s[3/2]1 cascade; the 6p′ → 7s → 6p cascade is also observed, although the secondary 7s → 6p emission is rather weak in comparison with excitation of the 7p states.