Superradiative transitions in argon and krypton

K. G. Ericsson, L. R. Lidholt

Maha Khaled Omar, W. D. Williams, Charles I. Sukenik

We report photoassociative spectroscopy performed separately on Kr84 and Ar40. The spectra were obtained as a function of laser intensity with the spectroscopy laser tuned around the ns[3/2]2→np[5/2]3 trapping transition, where n=4 for argon and n=5 for krypton. The resulting spectra are the first ever obtained for krypton on this important transition. This transition in argon was previously studied in our group. At that time, discrete features were observed in the spectrum, but their origin was not conclusively identified. We have now identified these features as artifacts from laser sidebands. We discuss the origin of these sidebands, how they imprint their presence on the spectra, and present spectra for argon with the artifacts removed. For both krypton and argon, while we observe photoassociation, we do not observe any resolved vibrational structure. We present a theoretical analysis of the expected vibrational level spacings based on calculated potential curves and show that the absence of resolved structure in the spectra of our experiments (as configured) is not surprising. Finally, we discuss the requirements of future experiments in which resolution of vibrational structure in this system might be obtained.

A.V. Andreev, P. V. Polevoy

Maha Khaled Omar, W. D. Williams, Charles I. Sukenik

We report photoassociative spectroscopy performed separately on Kr84 and Ar40. The spectra were obtained as a function of laser intensity with the spectroscopy laser tuned around the ns[3/2]2→np[5/2]3 trapping transition, where n=4 for argon and n=5 for krypton. The resulting spectra are the first ever obtained for krypton on this important transition. This transition in argon was previously studied in our group. At that time, discrete features were observed in the spectrum, but their origin was not conclusively identified. We have now identified these features as artifacts from laser sidebands. We discuss the origin of these sidebands, how they imprint their presence on the spectra, and present spectra for argon with the artifacts removed. For both krypton and argon, while we observe photoassociation, we do not observe any resolved vibrational structure. We present a theoretical analysis of the expected vibrational level spacings based on calculated potential curves and show that the absence of resolved structure in the spectra of our experiments (as configured) is not surprising. Finally, we discuss the requirements of future experiments in which resolution of vibrational structure in this system might be obtained.

Victor Nikolaevich Popov, Vladimir Sergeevich Yarunin

Maha Khaled Omar

Creating ultracold molecules has attracted considerable interest in the last decade. Once created, such molecules can be used for precision spectroscopy or to study chemical reactions at ultracold tem peratures. Several techniques have been developed to produce ultracold molecules; the most common is photoassociation where two ultracold atoms collide in the presence of light that induces a free-bound transition to an excited molecular state. Photoassociation can also be used to perform spectroscopy in order to map out the ro-vibrational levels of a molecular state. In this dissertaiotn, we report on our Photoasociative Spectroscopy (PAS) studies conducted separately in argon and krypton. For each species, we have studied transitions near two different atomic limits ns[3/2]2 —> np[5/2]2 and ns[3/2]2 —» np[5/2]3where n = 4 for argon and n = 5 for krypton. The former atomic transition is called the “quench transition” since it forms a strong coupled channel to the ground state. As a result for this strong coupling the original atomic sample is degraded and quenched. The latter transition is the one used to cool and confine the atoms and is known as the “trapping transition.” Spectroscopy near the trapping transition in argon was studied previously in our group [1] and specific features were observed in the spectrum. At the time, the features were not definitively identified, but more than one explanation was suggested for further testing. One possible explanation was that these features were a result of resonances happening at “doubly-excited” molecular levels. The population of such states could take place as a result of absorbing two photons of the same frequency which causes photoassociation. In this dissertation we report on a series of experiments that were performed to study and conclusively identify the origin of those features. These experiments led to the conclusion that the features in the spectra were an artifact of otherwise undetectable frequency sidebands on our semiconductor diode laser. Once identified as such, a new laser was constructed to repeat the spectroscopy measurements in argon and take new measurements in krypton that would be free from laser artifacts. In those spectra, no specific vibrational features were observed and resolved in either species. Results were consistent with published results obtained by other groups using other noble gases. Finally, we report on our attempts to perform PAS on a quench transition in order to confirm results obtained for krypton by another group [2]. We were not able to observe any photoassociation signal for both argon and krypton on this transition. We were able to observe similar effects to those reported in Ref. [2] but we attribute these to artifacts from an acousto-optic modulator and not as arising from molecular structure.