Photoassociation Spectroscopy Research Articles

Determination of the calcium ground state scattering length by photoassociation spectroscopy at large detunings

Photoassociation spectroscopy was used to determine the s-wave scattering length of 40Ca atoms in their electronic ground state. Vibrational levels were observed in an extended range of up to 182 GHz below the dissociation limit 4s2 1S0–4s4p 1P1. Thus, the frequency interval was nearly tripled, in which photoassociation was observed compared to previous measurements. The spectra were analyzed by means of quantum mechanical simulations. With the new data it was possible to resolve the discrepancy concerning the ground state scattering length presented in earlier publications [Phys. Rev. A 67, 043408 (2003); Eur. Phys. J. D 26, 155 (2003)]. An improved dipole-dipole coupling constant C3 Σ = 0.52306(20) ×103 cm-1 nm3 is obtained.

Determination of thes-Wave Scattering Length and theC6van der Waals Coefficient ofYb174via Photoassociation Spectroscopy

We report photoassociation spectroscopy of 174Yb for the 1S(0)-1P1 transition at 1 microK, where only the s-wave scattering state contributes to the spectra. The wave function of the s-wave scattering state is obtained from the photoassociation efficiency, and we determine that the C6 potential coefficient is 2300+/-250 a.u. and the s-wave scattering length is 5.53+/-0.11 nm. Based on these parameters, we discuss the scattering properties of s- and d-wave states.

Optical clock and ultracold collisions with trapped strontium atoms

With microkelvin neutral strontium atoms confined in an optical lattice, we have achieved a fractional resolution of better than 5 x 10−15 on the1 S o −3 P o doubly forbidden 87Sr clock transition at 698 nm. Measurements of the clock line shifts as a function of experimental parameters indicate that the fractional uncertainties due to systematic shifts could be reduced below 10−15. The ultrahigh spectral resolution permitted resolving the nuclear spin states of the clock transition at small magnetic fields, leading to measurements of the 3 P o magnetic moment and metastable lifetime. In addition, photoassociation spectroscopy was performed on the narrow 1 S o −3 P 1 transition of 88Sr, revealing the least-bound state, and showing promise for efficient optical tuning of the ground state scattering length and production of cold molecules.

Publisher's Note: Ultracold photoassociation spectroscopy: Long-range molecules and atomic scattering [Rev. Mod. Phys.78, 483 (2006)

Publisher's Note: Ultracold photoassociation spectroscopy: Long-range molecules and atomic scattering [Rev. Mod. Phys.78, 483 (2006)

Spin-dipole-induced lifetime of the least-boundΣg+5state ofHe(2S13)+He(2S13)

The properties of the least-bound vibrational level (v=14) of the quintet sigma state formed during the ultracold collision of two spin-polarized metastable helium atoms are crucial to studies of photoassociation spectroscopy of metastable helium. We report a calculation of the autoionization lifetime of this state induced by spin-dipole coupling of the quintet sigma state to the singlet sigma state from which Penning and associative ionization processes are highly probable. We find a lifetime of about 150 microseconds, significantly larger than the recent experimental estimates of (4-5) microseconds.

Ultracold photoassociation spectroscopy: Long-range molecules and atomic scattering

Photoassociation is the process in which two colliding atoms absorb a photon to form an excited molecule. The development of laser-cooling techniques for producing gases at ultracold !!1 mK temperatures allows photoassociation spectroscopy to be performed with very high spectral resolution. Of particular interest is the investigation of molecular states whose properties can be related, with high precision, to the properties of their constituent atoms with the “complications” of chemical binding accounted for by a few parameters. These include bound long-range or purely long-range vibrational states in which two atoms spend most or all of their time at large internuclear separations. Low-energy atomic scattering states also share this characteristic. Photoassociation techniques have made important contributions to the study of all of these. This review describes what is special about photoassociation spectroscopy at ultracold temperatures, how it is performed, and a sampling of results including the determination of scattering lengths, their control via optical Feshbach resonances, precision determinations of atomic lifetimes from molecular spectra, limits on photoassociation rates in a Bose-Einstein condensate, and briefly, production of cold molecules. Discussions are illustrated with examples on alkali-metal atoms as well as other species. Progress in the field is already past the point where this review can be exhaustive, but an introduction is provided on the capabilities of photoassociation spectroscopy and the techniques presently in use.

Narrow Line Photoassociation in an Optical Lattice

With ultracold 88Sr in a 1D magic wavelength optical lattice, we performed narrow-line photoassociation spectroscopy near the 1S0 - 3P1 intercombination transition. Nine least-bound vibrational molecular levels associated with the long-range 0u and 1u potential energy surfaces were measured and identified. A simple theoretical model accurately describes the level positions and treats the effects of the lattice confinement on the line shapes. The measured resonance strengths show that optical tuning of the ground state scattering length should be possible without significant atom loss.

Accurate Determination of the Scattering Length of Metastable Helium Atoms Using Dark Resonances between Atoms and Exotic Molecules

We present a new measurement of the s-wave scattering length a of spin-polarized helium atoms in the 2(3)S1 metastable state. Using two-photon photoassociation spectroscopy and dark resonances, we measure the energy E(nu)=14= -91.35+/- 0.06 MHz of the least-bound state nu = 14 in the interaction potential of the two atoms. We deduce a value of a=7.512+/-0.005 nm, which is at least 100 times more precise than the best previous determinations and is in disagreement with some of them. This experiment also demonstrates the possibility to create exotic molecules binding two metastable atoms with a lifetime of the order of 1 micros.

Spectroscopic Determination of thes-Wave Scattering Lengths ofSr86andSr88

We report the use of photoassociative spectroscopy to determine the ground-state s-wave scattering lengths for the main bosonic isotopes of strontium, 86Sr and 88Sr. Photoassociative transitions are driven with a laser red detuned by up to 1400 GHz from the 1S0-1P1 atomic resonance at 461 nm. A minimum in the transition amplitude for 86Sr at -494 +/- 5 GHz allows us to determine the scattering lengths 610a0 < a86 < 2300a0 for 86Sr and a much smaller value of -1a0 < a88 < 13a0 for 88Sr.

Photoassociative Spectroscopy at Long Range in Ultracold Strontium

We report photoassociative spectroscopy of 88Sr(2) in a magneto-optical trap operating on the 1S0-->3P1 intercombination line at 689 nm. Photoassociative transitions are driven with a laser red detuned by 600-2400 MHz from the 1S0-->1P1 atomic resonance at 461 nm. Photoassociation takes place at extremely large internuclear separation, and the photoassociative spectrum is strongly affected by relativistic retardation. A fit of the transition frequencies determines the 1P1 atomic lifetime (tau=5.22+/-0.03 ns) and resolves a discrepancy between experiment and recent theoretical calculations.

Photoassociation spectroscopy of cold alkaline-earth-metal atoms near the intercombination line

The properties of photoassociation (PA) spectra near the intercombination line (the weak transition between $^{1}S_{0}$ and $^{3}P_{1}$ states) of group II atoms are theoretically investigated. As an example we have carried out a calculation for Calcium atoms colliding at ultra low temperatures of 1 mK, 1 $\mu$K, and 1 nK. Unlike in most current photoassociation spectroscopy the Doppler effect can significantly affect the shape of the investigated lines. Spectra are obtained using Ca--Ca and Ca--Ca$^*$ short-range {\it ab initio} potentials and long-range van der Waals and resonance dipole potentials. The similar van der Waals coefficients of ground $^{1}S_{0} + ^{1}S_{0}$ and excited $^{1}S_{0} + ^{3}P_{1}$ states cause the PA to differ greatly from those of strong, allowed transitions with resonant dipole interactions. The density of spectral lines is lower, the Condon points are at relatively short range, and the reflection approximation for the Franck-Condon factors is not applicable, and the spontaneous decay to bound ground-state molecules is efficient. Finally, the possibility of efficient production of cold molecules is discussed.

Prospects for measurement and control of the scattering length of metastable helium using photoassociation techniques

A numerical investigation of two-laser photoassociation (PA) spectroscopy on spin-polarized metastable helium (He*) atoms is presented within the context of experimental observation of the least-bound energy level in the scattering potential and subsequent determination of the s-wave scattering length. Starting out from the model developed by Bohn and Julienne [Phys. Rev. A \textbf{60}, (1999) 414], PA rate coefficients are obtained as a function of the parameters of the two lasers. The rate coefficients are used to simulate one- and two-laser PA spectra. The results demonstrate the feasibility of a spectroscopic determination of the binding energy of the least-bound level. The simulated spectra may be used as a guideline when designing such an experiment, whereas the model may also be employed for fitting experimentally obtained PA spectra. In addition, the prospects for substantial modification of the He* scattering length by means of optical Feshbach resonances are considered. Several experimental issues relating to the numerical investigation presented here are discussed.

Photoassociation experiments with ultracold metastable helium

The present article gives a review of various photoassociation (PA) experiments performed at ENS with a gas of ultracold atoms of metastable helium in the 23S1 state, using a PA laser beam red-detuned from the 23S1-23P transitions. Molecular spectra close to the D2 atomic line (23S $_1\leftrightarrow 2^3$ P2) are presented. All the measured lines are identified as a signature of molecular bound states having a strong (if not pure) quintet spin character at short interatomic distance. Close to the D0 atomic line (23S $_1\leftrightarrow 2^3$ P0), giant helium dimers can be produced [see Phys. Rev. Lett. 91, 073203 (2003)]. A laser set-up improved recently allows us to measure very accurately the binding energy of the ro-vibrational ground state of the 0 u + purely long-range potential and the agreement with the theory published previously is excellent. Finally, preliminary results on 2 photon PA spectroscopy are given.

Photoassociative formation of ultracold polar KRb molecules

We investigate the effectiveness of creating polar ground-state KRb molecules by two-color photoassociative spectroscopy. In this process the molecules are formed from ultra-cold samples of K and Rb. Focusing on spin-polarized atoms we show that an effective pathway exists. In addition, we investigate the stability of the polar molecules in the presence of a thermal black-body radiation field.

Photoassociation spectroscopy of ultracold Cs below the 6P(3/2) limit.

High precision photoassociation spectroscopy is performed in ultracold cesium gas, with detunings as large as 51 cm(-1) below the Cs(6S(1/2))+Cs(6P(3/2)) asymptote. Trap-loss fluorescence detection is used for detecting the photoassociation to excited state ultracold molecules. Long vibrational progressions are assigned to electronic states of 0(g) (-), 0(u) (+), and 1(g) symmetry. The spectral data are fitted to a LeRoy-Bernstein equation, in order to obtain the effective coefficients of the leading long-range interaction term (C(3)/R(3)) and the relative vibrational quantum numbers measured down from dissociation. Additionally we present evidence for perturbations between the 0(g) (-) state and the dark 2(u) state.

Photoassociation spectroscopy of laser-cooled ytterbium atoms.

We report the photoassociation spectroscopy of laser-cooled ytterbium atoms in an optical trap. We observed more than 90 photoassociation resonances of vibrational levels in the (1)Sigma(+)(u) state, including 80 consecutive series, up to 490 GHz detuning with respect to the atomic resonance. From the resonance frequencies we derived the atomic radiative lifetime of the (6s6p) 1P1 state to be 5.464+/-0.005 ns, which is about 2 orders of magnitude improvement over previous results. We also observed line broadening of resonances, which is ascribed to the predissociation to the triplet states, and estimated the transition probability to be 0.2. Furthermore, we observed the decrease of the photoassociation signal intensity, from which the scattering length is estimated to be equal to or less than 3 nm.

Photoassociation spectroscopy of ultracold Cs below the 6P1/2 limit.

We have performed high precision photoassociation spectroscopy of ultracold cesium gas. Using trap-loss fluorescence detection and controlling the background cesium pressure we were able to photoassociate atoms into excited states of ultracold molecules with large detunings up to 56 cm(-1) below the Cs(6S(1/2)) + Cs(6P(1/2)) atomic asymptote. Vibrational progressions are assigned to 0(g)(-), 0(u)(+), and 1(g) long-range states. By fitting the spectral data to the LeRoy-Bernstein expression, the effective coefficients of the leading long-range interactions and the vibrational quantum number at dissociation are obtained. In addition we have observed spectral perturbations between states of the same symmetry belonging to different asymptotes (6P(1/2) and 6P(3/2)). The perturbations are manifested through irregular vibrational level spacings and are especially pronounced in the 0(u)(+) symmetry. Many observed rotational levels indicate d- and higher partial wave contributions to the photoassociation cross section in the presence of trapping laser light, while spectral regions with only weak features suggest nodes in the lower state wave functions corresponding to the two ground state atoms asymptote.

Accurate asymptotic ground state potential curves of Cs $\mathsf{_2}$ from two-colour photoassociation

Over 100 high lying level energies of the lowest electronic states $X^1{\rm\Sigma}^ + _g$ and $a^3{\rm\Sigma}^ + _u$ in Cs2 are determined in a $\Lambda$ -like scheme two-colour photoassociation spectroscopy. The results are analyzed with a coupled channel model using an asymptotic approach, based on nodal lines. From this analysis we determine the long range dispersion coefficient C6 to 6846.2 $\pm$ 15.6 a.u. We also obtain the first experimental determination of the amplitude of the asymptotic exchange term.

Photoassociation spectroscopy of ultra-cold long-range molecules

Spectroscopic study of so-called long-range molecules, with average interatomic distances much larger than usual for chemical bonds, is conveniently performed by photoassociation (PA) of ultracold atoms. We present here a review of our results obtained by one and two-photon PA spectroscopy of the Cs 2 molecule, using as intermediate the 0 g − and 1 u potentials correlated to the (6 s+6 p 3/2) asymptote. These results have been interpreted using an asymptotic theoretical approach, which was specifically build for such long-range molecules. To cite this article: N. Vanhaecke et al., C. R. Physique 5 (2004).

Improved LeRoy-Bernstein near-dissociation expansion formula, and prospect for photoassociation spectroscopy.

NDE (Near-dissociation expansion) including LeRoy-Bernstein formulas are improved by taking into account the multipole expansion coefficients and the nonasymptotic part of the potential curve. The theory is tested with the Rydberg-Klein-Rees (RKR) potential curve of the Cs(2)(0(g) (-)6s+6p(3/2)) state. Results indicate that the formula could be used to improve the determination of the asymptotic coefficient (within a 1% accuracy) and to extract relativistic correction from photoassociation spectra of long-range potential curve of diatomic molecules.