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Anisotropy of optical suppression in photoassociative ionization collisions\nwithin a slow, collimated sodium atom beam

C.-C. Tsao, Y. Wang, R. Napolitano, J. Weiner

Published Jul 12, 2013• 0 citations
OpenAlex

Abstract

\n We report the observation of polarization anisotropy in the optical\nsuppression of photoassociative ionization (PAI) collisions. Binary\ncollisions occur within a tightly collimated and optically cooled velocity\ngroup of a single sodium beam. A laser beam, blue-detuned with respect to\nthe atomic resonance transition, crosses the atomic beam and suppresses the\nPAI rate. We measure this suppression as a function of intensity and\nelectric field vector aligned parallel or perpendicular to the atomic beam\naxis. Quantum close-coupling and multichannel curve-crossing calculations of\nmodel systems yield insight into the nature of the anisotropy and are in\nreasonable agreement with the measurements.\n\n \n

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\n We report the observation of polarization anisotropy in the optical\nsuppression of photoassociative ionization (PAI) collisions. Binary\ncollisions occur within a tightly collimated and optically cooled velocity\ngroup of a single sodium beam. A laser beam, blue-detuned with respect to\nthe atomic resonance transition, crosses the atomic beam and suppresses the\nPAI rate. We measure this suppression as a function of intensity and\nelectric field vector aligned parallel or perpendicular to the atomic beam\naxis. Quantum close-coupling and multichannel curve-crossing calculations of\nmodel systems yield insight into the nature of the anisotropy and are in\nreasonable agreement with the measurements.\n\n \n
Summary form only given. Collisions with cooled and trapped atoms have been the subject of intense investigation during the past years. Unprecedented details of the intermediate steps in the collision have been revealed. A remarkable feature in the ultracold system is the ability to control entrance-channel scattering flux and thereby control the exit channel of the collisional encounter. Here we present the continuation of our recent work where photoassociative ionizations (PAI) of sodium atoms were suppressed by application of an optical field. The new experiments show that suppression of almost 100% is possible when high intensity is used and a remarkable dependence with the polarization of the suppressor laser field is observed and calculated. This result shows a deviation from the simple picture based on the Landau-Zener avoided crossing model when high intensity is used.
Three-dimensional quantum scattering calculations predict that the degree of optical shielding of cold collisions saturates with increasing intensity very differently from two-state models and is sensitive to the polarization of the shielding light. We report measurements showing how suppression of Na photoassociative ionization (PAI) rates is sensitive to the intensity and polarization of the shielding laser. At higher intensities, circular polarization suppresses PAI rates an order of magnitude more effectively than linear polarization, in qualitative agreement with our model calculations.
We report measurements of cold photoassociative ionization (PAI) spectra obtained from collisions within a slow, bright Na atomic beam. A high-brightness atom flux, obtained by optical cooling and focusing of the atom beam, permits a high degree of alignment and orientation of binary collisions with respect to the laboratory atom-beam axis. The results reveal features of PAI spectra not accessible in conventional magneto-optical trap studies. We take advantage of this high degree of alignment to selectively excite autoionizing doubly excited states of specific symmetry.
We report here measurements of two-body photoassociative ionization collisions between sodium atoms within an ultranarrow velocity class selected from a well-collimated, thermal atomic beam. Doppler-shifted excitation of the Na(3s2{\mathrm{}}^{2}2S1/2{\mathit{S}}_{1/2}S1/2​;F=1)\ensuremath{\rightarrow}Na(5p2{\mathrm{}}^{2}2P3/2{\mathit{P}}_{3/2}P3/2​) transition at 285 nm by a single-mode laser defines the narrow velocity class that subsequently populates the F=2 hyperfine level of the Na ground state by optical pumping. Probe laser beam excitation tuned near the Na(3s2{\mathrm{}}^{2}2S1/2{\mathit{S}}_{1/2}S1/2​;F=2)\ensuremath{\rightarrow}Na(3p2{\mathrm{}}^{2}2P3/2{\mathit{P}}_{3/2}P3/2​;F=3) transition produced photoassociative ionization with an average collision energy EK{\mathit{E}}_{\mathit{K}}EK​ corresponding to a temperature of 5.3 mK (EK{\mathit{E}}_{\mathit{K}}EK​=3/2kT). We determine the rate constant for the process as a function of probe beam intensity and polarization.