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Optics Letters

Observation of a laser-induced dipole–quadrupole collision

William R. Green, M. D. Wright, Jacques Lukasik, J. F. Young, Stephen E. Harris

Published Sep 1, 1979• 32 citations
Publisher

Abstract

Experimental observation of a laser-induced dipole-quadrupole collision between Sr and Ca is reported. The laser-induced collision cross section peaks at an applied photon energy equal to the energy defect of the initial and final states of the infinitely separated atoms. A cross section of 3 x 10(-14) cm(2) was induced at a laser-power density of 7 x 10(9) W/cm(2); the linewidth was 20 cm(-1).

DOI
10.1364/ol.4.000265

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Experimental observation of a laser-induced dipole-quadrupole collision between Sr and Ca is reported. The laser-induced collision cross section peaks at an applied photon energy equal to the energy defect of the initial and final states of the infinitely separated atoms. A cross section of 3 x 10(-14) cm(2) was induced at a laser-power density of 7 x 10(9) W/cm(2); the linewidth was 20 cm(-1).
A three-state model for calculating the cross section of laser-induced dipole-quadrupole collisional energy transfer in Sr-Ca system is presented. The motion equations for the probability amplitudes of the three intermediate states are obtained. The expression of the cross section is derived. Various factors including field intensity, relative speed, system temperature which influence the collisional cross section are discussed to illustrate the features of the dipole-quadrupole laser-induced collisional energy transfer (LICET)process. Calculating results show that the peak of the LICET profiles moves to the red, the tuning range of the profiles obviously becomes narrower with the laser field intensity increasing and a cross section of 1.25 × 10(-13)cm(2) at a laser intensity of 8.29 × 10(9)W/cm(2) is obtained. Our results indicate that dipole-quadrupole LICET process can be the effective way to transfer energy selectively from a storage state of arbitrary parity to a target state of arbitrary parity.
Experimental studies of two laser-induced charge-transfer reactions in Ca and Sr are presented. In both reactions, a Ca ion collides with an Sr neutral in the presence of a laser field to produce a Ca neutral and an excited Sr ion. The two reactions differ in the final level of the Sr+{\mathrm{Sr}}^{+}Sr+ species. The collision cross sections associated with these reactions are studied as functions of applied laser frequency and power density. The largest cross section induced is equal to ${10}^{\ensuremath{-}16}$ cm2{\mathrm{cm}}^{2}cm2, obtained at a power density of 2\ifmmode\times\else\texttimes\fi{}109{10}^{9}109 W/cm2{\mathrm{cm}}^{2}cm2. Differences in experimental results associated with the two reactions are explained qualitatively by an examination of the potential curves of the CaSr+{\mathrm{Sr}}^{+}Sr+ quasimolecule.
A laser induced quadrupoledipole collisional energy transfer system of CaSr is proposed and the four-state quadrupoledipole laser induced collisional energy transfer model is presented.The excitation spectrum calculated for the CaSr system is characterized by a doublet structure and a width which is about twice wider than the dipoledipole laser induced collisional energy transfer results.Calculating results show that the full width at half peak of the prole becomes larger and the quasi-static wing tends to be a broad at as the eld intensity increases, which are dierent from the reported results of dipoledipole laser induced collisional energy transfer processes, dipolequadrupole and quadrupolequadrupole.A cross-section of 2.48 × 10 -14 cm 2 at a laser eld intensity of 5.21 × 10 7 V/m is obtained which indicates that the quadrupoledipole process can be an eective way to transfer energy selectively.
Observations are made of dipole-quadrupole laser-induced inelastic collisions occurring during the collision of two Ba atoms. Results for both stimulated-absorption and spontaneous-emission experiments using the same collisional configuration are reported for the first time. In both experiments the interaction maximizes at the $R=\ensuremath{\infty}$ wavelength and has a full-width-at-half-maximum linewidth of \ensuremath{\sim}8 ${\mathrm{cm}}^{\ensuremath{-}1}$. These results bear on the study of the interatomic potentials for colliding atoms and permit the collisional energy transfer to states hitherto inaccessible to dipole-dipole collisions.
We report the observation of a laser-induced charge-transfer collision. In the presence of an intense laser beam, ground-state calcium ions collide with ground-state strontium atoms, selectively producing excited strontium ions and calcium neutrals. The laser-induced collision cross section has a linewidth of about 50 ${\mathrm{cm}}^{\ensuremath{-}1}$ and peaks \ensuremath{\sim} 70 ${\mathrm{cm}}^{\ensuremath{-}1}$ from that wavelength which satisfies the energy defect of the separated atoms.
We describe two new experiments which demonstrate laser-induced inelastic collisions. Energy was stored in the Sr 5p1Po5p^{1}P^{o}5p1Po state and selectively transferred both to the Ca $4{p}^{2}^{1}S$ and 5d1D5d^{1}D5d1D states. The collision cross sections maximized at the interatomic wavelengths of 4977 and 4711 \AA{}, respectively, and had a half-power width of about 14 ${\mathrm{cm}}^{\ensuremath{-}1}$.