Two-colour photoassociation spectroscopy of ultracold sodium

Abstract

We demonstrate a number of two-colour spectroscopy techniques where the first step is the photoassociation of laser-cooled and trapped sodium atoms to form bound states of Na 2 . High-resolution (∼ 0.001 cm −1 ) spectra of Na 2 are obtained. Spectra of the 0 − g (3S + 3P 3/2 ) 'purely long-range' state demonstrates the use of two-colour spectroscopy to open up an ionization channel for detecting the occurrence of photoassociation. The utility of photoassociation as a technique for producing cold molecular samples in a well defined rovibrational state is demonstrated with spectra showing bound → bound and bound → free (Condon internal diffraction) transitions after the photoassociation. Starting from states in the 0 − g and 1 g (3S + 3P 3/2 ) potentials, these transitions include upward transitions to autoionizing potentials dissociating near 3P + 3P and downward transitions back to the 3S + 3S ground-state potentials. Spectroscopic constants for six levels of a doubly excited 1 u state of Na 2 are given.

Photoassociation of a Bose-Einstein Condensate near a Feshbach Resonance

“…The predicted universal rate limit remains elusive. Previous experiments have also measured an intensity-dependent spectral redshift of the PA resonance [8,9,14], which has been ascribed to light-induced coupling to the continuum [15][16][17]. In this Letter, measurements of the PA rate coefficient K p and the spectral shift are presented in the vicinity of a magnetic FR of 7 Li for both a thermal gas and a BEC.…”

“…The spectral shift is a consequence of light-induced mixing of nearby molecular states into f R , and has been shown to scale linearly with f R C [16]. In previous single-photon experiments the shift was dominated by coupling to the continuum, resulting in a redshift [17]. In the case of PA near a FR, however, the shift is strongly affected by the underlying closed-channel molecular state responsible for the FR.…”

Photoassociation of Ultracold Atoms: A New Spectroscopic Technique

“…Ladder-type two-color photoassociative OODR experiments have been carried out for K 2 (37,63,88) and for Na 2 (49,83,84,86,105). Figure 18 shows representative direct ionization signals for three (4s ϩ 6s, 4s ϩ 5d, 4s ϩ 6d) of the five asymptotes studied (4s ϩ 4d and 4s ϩ 7s are not shown).…”

Light forces in ultracold photoassociation

“…The PA transition to the 1 g level is weakly allowed by singlet-triplet mixing, but it still presents a relatively strong one-color ionization signal. This level has been the subject of many previous photoassociation studies [12,13,14,15,16]. The use of a weak transition allows the resolution of rotational levels at high intensities, which otherwise might be unresolved due to power broadening and state mixing.…”