Characteristic oscillations in the coherent transients of ultracold rubidium molecules using red and blue detuned pulses for photoassociation

Abstract

We investigate the interaction of femtosecond laser pulses with an ensemble of ultracold rubidium atoms by applying shaped excitation pulses with two different types of spectral filtering. Although the pulses, which are frequency filtered with a high pass, have no spectral overlap with molecular states, we observe coherent molecular transients. Similar transients obtained with nearly transform-limited pulses, where only the atomic resonance is removed, reveal two differing oscillatory components. The resulting transients are compared among themselves and supported with quantum dynamical simulations which indicate a photoassociation process. The effect is due to the strong field interaction of the pulse with the colliding atom pair.

Formation of ultracold Rb2 molecules in the v′′ = 0 level of the a3Σ+u state via blue-detuned photoassociation to the 13Πg state

“…Blue-detuned PA, where vibrational levels are energetically above their corresponding atomic asymptote, was first proposed to probe quasibound states 3 and form ultracold Rb 2 4 and KRb molecules 5 . Blue-detuned PA was first observed in Cs 2 6 and Rb 2 7 . There are two cases where blue-detuned photoassociation could occur: (1) in a local minimum of a potential energy curve repulsive at long range (as in the case here with the 1 3 Π g state of Rb 2 ) or (2) in a well that contains a potential barrier and vibrational levels above the atomic asymptote (for instance the 2 1 Σ + g state in Rb 2 8 ).…”

“…5 Blue-detuned photoassociation was first observed 6 in our laboratory; however, molecular assignments have remained elusive due to relatively small signals. Blue-detuned photoassociation has also been observed using an intense femtosecond laser, 7 which simultaneously drove resonant and non-resonant transitions to a variety of states, making molecular assignments difficult to perform.…”

Correlation dynamics after short-pulse photoassociation

“…It represents a non-stationary state of the two-atom scattering whose evolution in time can be monitored by a suitably chosen probe pulse. Such a pump-probe spectroscopy of pair correlations can be implemented by slight modification of existing experimental setups [24][25][26][27][28]. It can be applied to Bose-Einstein condensates as well as thermal ultracold gases.…”

“…In the ultracold regime, first experiments aimed at femtosecond photoassociation of rubidium dimers have led to dissociation of molecules created by the trap lasers rather than association [22,23]. Recently, evidence of coherent formation of molecules in the electronically excited state was provided in a pump-probe experiment with chirped femtosecond laser pulses [24][25][26][27][28]. The proven experimental ability of * Electronic address: ckoch@physik.fu-berlin.de pulsed photoassociation paves the way for developing a pump-probe spectroscopy to study ultracold two-atom correlation dynamics [7].…”

Formation of85Rb2ultracold molecules via photoassociation by two-color laser fields modulating the Gaussian amplitude

“…Moreover, the optimization of chirped laser pulses can keep the adiabaticity condition within the PA window [15]. Frequency cutoff pulses can suppress losses by atomic transitions [16][17][18]. The slowly-turned-on and rapidlyturned-off (STRT) laser pulses can maintain the population of off-resonantly vibrational levels [19,20].…”