We report beam-loss photoassociation (PA) spectra of cold collisions within a slow, bright Na atom beam near the ${D}_{1}$ resonance line. The high collimation and brilliance of the atomic beam permits the detection of atomic fluorescence loss resulting from the photoassociation of cold sodium atoms. The results show that even at high PA laser intensities, where strong coupling of the colliding atoms to the optical field might obscure spectral features, vibrational and rotational progressions are surprisingly well resolved. We attribute the conservation of narrow spectral features to the properties of the saturated line shapes and to the unconventional collision energy distribution in one-dimensional (1D) single-beam collisions compared to 3D collisions in a gas cell.We report beam-loss photoassociation (PA) spectra of cold collisions within a slow, bright Na atom beam near the ${D}_{1}$ resonance line. The high collimation and brilliance of the atomic beam permits the detection of atomic fluorescence loss resulting from the photoassociation of cold sodium atoms. The results show that even at high PA laser intensities, where strong coupling of the colliding atoms to the optical field might obscure spectral features, vibrational and rotational progressions are surprisingly well resolved. We attribute the conservation of narrow spectral features to the properties of the saturated line shapes and to the unconventional collision energy distribution in one-dimensional (1D) single-beam collisions compared to 3D collisions in a gas cell.

Physical Review AApr 9, 20047 citations

Theory of velocity-dependent, collision-broadened, Doppler-free line shapes

M. J. O’Callaghan, J. Cooper

Line-shape expressions for two-step resonant excitation in the presence of low-pressure perturbers are derived. These expressions allow for velocity-dependent broadening rates and are well suited for studying the line-shape contributions due to coherent excitation, incoherent excitation (due to dephasing collisions), interference between coherent and incoherent excitation, and velocity-changing collisions. Using the sodium 3S-3P-4D system perturbed by noble-gas atoms as an example and assuming ${C}_{6}$ interaction potentials, line shapes at a variety of laser detunings (Doppler selected atomic velocities) are numerically calculated to study variation in the line shape due to competing excitation paths and speed-dependent collision rates. In order to deal with both the line core and the line wing a composite collision kernel consisting of a Lorentzian kernel for small \ensuremath{\Delta} ${v}_{z}$ collisions and a Keilson-Storer kernel for large \ensuremath{\Delta} ${v}_{z}$ collisions is used. It is also demonstrated how the inelastic (3 ${P}_{3/2}$ -3 ${P}_{1/2}$ ) velocity-changing collision kernel may be obtained from experimental data at low pressures. Theoretical line shapes and broadening rates are compared with experiment.Line-shape expressions for two-step resonant excitation in the presence of low-pressure perturbers are derived. These expressions allow for velocity-dependent broadening rates and are well suited for studying the line-shape contributions due to coherent excitation, incoherent excitation (due to dephasing collisions), interference between coherent and incoherent excitation, and velocity-changing collisions. Using the sodium 3S-3P-4D system perturbed by noble-gas atoms as an example and assuming ${C}_{6}$ interaction potentials, line shapes at a variety of laser detunings (Doppler selected atomic velocities) are numerically calculated to study variation in the line shape due to competing excitation paths and speed-dependent collision rates. In order to deal with both the line core and the line wing a composite collision kernel consisting of a Lorentzian kernel for small \ensuremath{\Delta}${v}_{z}$ collisions and a Keilson-Storer kernel for large \ensuremath{\Delta}${v}_{z}$ collisions is used. It is also demonstrated how the inelastic (3${P}_{3/2}$-3${P}_{1/2}$) velocity-changing collision kernel may be obtained from experimental data at low pressures. Theoretical line shapes and broadening rates are compared with experiment.

Physical Review AJun 1, 198923 citations

Theory of saturation spectroscopy including collisional effects

P. R. Berman, P. F. Liao, John E. Bjorkholm

A theory of saturation spectroscopy in three-level gas-vapor systems, including collisional effects, is presented. Using a model of collisions in which they are phase interrupting in their effect on level coherences and velocity changing in their effect on level population densities, the authors calculate the absorption profile of a weak probe field on a given transition when an arbitrarily strong pump field acts on a coupled transition. Line shapes are derived for an arbitrary collision kernel describing the velocity-changing collisions, and these line shapes are evaluated for the collision kernel proposed by Keilson and Storer. Various limiting forms for the line shapes are derived and representative line shapes are displayed. Several new features of the line shapes, including collisionally induced increased probe absorption are discussed. The line shapes are seen to reflect the various collisional processes that may occur in atomic or molecular systems.A theory of saturation spectroscopy in three-level gas-vapor systems, including collisional effects, is presented. Using a model of collisions in which they are phase interrupting in their effect on level coherences and velocity changing in their effect on level population densities, the authors calculate the absorption profile of a weak probe field on a given transition when an arbitrarily strong pump field acts on a coupled transition. Line shapes are derived for an arbitrary collision kernel describing the velocity-changing collisions, and these line shapes are evaluated for the collision kernel proposed by Keilson and Storer. Various limiting forms for the line shapes are derived and representative line shapes are displayed. Several new features of the line shapes, including collisionally induced increased probe absorption are discussed. The line shapes are seen to reflect the various collisional processes that may occur in atomic or molecular systems.

Physical Review ADec 1, 197927 citations

We report beam-loss photoassociation (PA) spectra of cold collisions within a slow, bright Na atom beam near the

{D}_{1}

resonance line. The high collimation and brilliance of the atomic beam permits the detection of atomic fluorescence loss resulting from the photoassociation of cold sodium atoms. The results show that even at high PA laser intensities, where strong coupling of the colliding atoms to the optical field might obscure spectral features, vibrational and rotational progressions are surprisingly well resolved. We attribute the conservation of narrow spectral features to the properties of the saturated line shapes and to the unconventional collision energy distribution in one-dimensional (1D) single-beam collisions compared to 3D collisions in a gas cell.

{C}_{6}

interaction potentials, line shapes at a variety of laser detunings (Doppler selected atomic velocities) are numerically calculated to study variation in the line shape due to competing excitation paths and speed-dependent collision rates. In order to deal with both the line core and the line wing a composite collision kernel consisting of a Lorentzian kernel for small \ensuremath{\Delta}

{v}_{z}

collisions and a Keilson-Storer kernel for large \ensuremath{\Delta}

{v}_{z}

collisions is used. It is also demonstrated how the inelastic (3

{P}_{3/2}

-3

{P}_{1/2}

) velocity-changing collision kernel may be obtained from experimental data at low pressures. Theoretical line shapes and broadening rates are compared with experiment.