n this presentation, we discuss results from two separate bodies of work. In the first, we investigate all-optical excitation methods to produce metastable-state krypton. The high energies required to excite rare gases out of their ground state present a unique challenge in the context of laser experiments. Laser physics work with rare gases often relies on excitation within an RF discharge. All-optical excitation is a promising replacement for RF discharges, avoids problems caused by ion production and may eventually allow for higher efficiencies. We examine three separate methods of all-optical metastable-state production: using an ArF excimer laser, using the third harmonic of the Jefferson Lab free-electron laser (FEL), and using a commercially available UV lamp. In the second body of work, we perform photoassociation spectroscopy in an ultracold, heteronuclear Rb + Ar* system. Photoassociation is a method that may be used to both 1) produce ultracold molecules, and 2) perform high-resolution spectroscopy on excited molecular states. Most work within the field has been performed within all alkali-metal systems. We examine a unique noble gas–alkali system within a dual species magneto-optical trap. We have performed a comprehensive search for evidence of excitation to molecular levels of RbAr. We illuminate atom pairs with a photoassociation laser in a spectral region detuned a few GHz below an atomic asymptote of argon, analogous to previous work in the homo-nuclear argon or krypton systems. We discuss our methodology and findings. We conclude with a discussion of how our results may be applied to future spectroscopic searches
n this presentation, we discuss results from two separate bodies of work. In the first, we investigate all-optical excitation methods to produce metastable-state krypton. The high energies required to excite rare gases out of their ground state present a unique challenge in the context of laser experiments. Laser physics work with rare gases often relies on excitation within an RF discharge. All-optical excitation is a promising replacement for RF discharges, avoids problems caused by ion production and may eventually allow for higher efficiencies. We examine three separate methods of all-optical metastable-state production: using an ArF excimer laser, using the third harmonic of the Jefferson Lab free-electron laser (FEL), and using a commercially available UV lamp. In the second body of work, we perform photoassociation spectroscopy in an ultracold, heteronuclear Rb + Ar* system. Photoassociation is a method that may be used to both 1) produce ultracold molecules, and 2) perform high-resolution spectroscopy on excited molecular states. Most work within the field has been performed within all alkali-metal systems. We examine a unique noble gas–alkali system within a dual species magneto-optical trap. We have performed a comprehensive search for evidence of excitation to molecular levels of RbAr. We illuminate atom pairs with a photoassociation laser in a spectral region detuned a few GHz below an atomic asymptote of argon, analogous to previous work in the homo-nuclear argon or krypton systems. We discuss our methodology and findings. We conclude with a discussion of how our results may be applied to future spectroscopic searches
This dissertation presents the findings of two experimental investigations in ultracold atomic and molecular physics: The study of the dual species trap loss in a rubidium - metastable argon magneto-optical trap and the photoassociative spectroscopy of ultracold metastable argon. The interspecies trap loss rate coefficients have been measured for ultracold collisions between 85Rb and 40Ar* in a dual-species magneto-optical trap (MOT) and the two rates have been found to be approximately equal over the range of intensities studied with values of β'Rb–Ar* = 3.0 ± 1.3 × 10-11 cm3/s and β'Ar*–Rb = 1.9 ± 0.9 × 10-11 cm3/s where β' Rb–Ar* is the trap loss coefficient for Rb in the presence of Ar* and β'Ar*–Rb is the reciprocal term. In addition, the trap loss rate coefficient for cold collisions in a metastable argon MOT alone have been measured with an average value of β Ar* = 5.2 ± 1.6 × 10-10 cm3/s. Using a quadrupole mass spectrometer, the production of Ar +, Ar+2, Rb+, and RbAr+ ions in the dual MOT have been observed, clearly identifying heteronuclear Penning and associative ionization as trap loss mechanisms. In the second experiment, the first ever investigation of the photoassociative (PA) spectroscopy of Ar* has been made. The exploratory study focuses on PA spectroscopy near the 4s[3/2]2 + 4p[5/2]3 asymptote of the Ar2* diatomic molecule over a 10 GHz range red detuned of the atomic resonance. With a range of probe laser intensities from ∼ 102–105ISat, 12 resonances have been observed. The spectra have been analyzed using the near-dissociation LeRoy-Bernstein method. Through this analysis, the spectra seem to best correlate with excitations to the 5g state.
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.
Heteronuclear polar molecules have recently attracted enormous attention owing to their ground state having a large electric dipole moment. The long range anisotropic dipole-dipole interaction in such systems is the basis for a variety of applications including quantum computing, precision measurements, ultracold chemistry and quantum simulations. Heteronuclear bi-alkali molecules, only a small subset of polar molecules, have received special attention mainly because the constituent alkali atoms are easy to laser cool and can be relatively easily associated to form molecules at ultracold temperatures. Our choice, the LiRb molecule, is motivated by the relatively high dipole moment (4.1 Debye) of the LiRb molecule in its rovibronic ground state. In this thesis, we study the LiRb molecule using laser spectroscopy and report, for the first time, the production of ultracold LiRb molecules by photoassociation (PA). The LiRb molecule is the least studied among all bi-alkali molecules and the first spectroscopic measurements on hot vapor phase LiRb molecules were reported only in 2011. We describe these measurements and their significance in chapter 2, after a brief introduction to the field of ultracold polar molecules in chapter 1. In chapter 3, we discuss our apparatus for simultaneous cooling and trapping of Li and Rb atoms in a dual-species magneto-optical trap (MOT) and report the measurement of interspecies collision-induced losses. In chapter 4, we describe the production of ultracold LiRb molecules in excited electronic states by photoassociation (PA). We report the measurements of the C6 coefficients for the Li (2s 2S1/2) + Rb (5p 2P1/2) and the Li (2s 2S1/2) + Rb (5p 2P3/2) asymptotes. We find a molecule formation rate (PLiRb) as high as 3.5x107 s-1 and a PA rate coefficient (KPA) as high as 1.3x10-10 cm3/s, the highest among heteronuclear bi-alkali molecules. In chapter 5, we discuss results on two-photon PA and we conclude, in chapter 6, with a road roadmap of future experiments for the production and detection of ultracold LiRb molecules in their rovibronic ground state.
This thesis describes the spectroscopy work on ultracold 39K 85Rb molecules as part of our effort towards producing ground-state ultracold polar molecules. ^ The starting points of our experiment are laser cooled and trapped K and Rb atoms in dual-species MOTs and the molecule formation method is photoassociation (PA). A fraction of the PA-produced excited-state molecules can spontaneously emit to the two lowest electronic states, the X 1Σ + state and the a 3Σ + state, to form high vibrational level molecules. In order to develop a population transfer scheme to make deeply bound molecules, we have studied the spectroscopy of KRb in several steps. Besides the PA step, we have also carried out a state-selective detection experiment to study the population distribution of the high vibrational level molecules formed via spontaneous emission. The detection method is pulsed-laser based ion time-of-flight mass spectroscopy. Due to the linewidth limitations of the pulsed laser, this detection method can only resolve vibrational structures. A cw laser induced ion depletion spectroscopy technique has been developed in order to obtain rotational resolution. Using this ion depletion method, we have studied a possible stimulated Raman transfer scheme via the 3 1Σ+ state. To this end, we have obtained all the spectroscopic information required to produce deeply bound KRb molecules in a single vibrational and rotational level. ^ Several other spectroscopic studies using the high vibrational level ultracold molecules are also discussed. ^
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.
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.