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Bulletin of the American Physical Society

Formation of ultracold molecules induced by a high-power single frequency fiber laser

Henry Fernandes Passagem, Ricardo Colín‐Rodríguez, Paulo Ventura da Silva, Nadia Bouloufa-Maafa, Olivier Dulieu, Luís Gustavo Marcassa

Published Jun 6, 2017• 0 citations
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Abstract

The influence of a high-power single-frequency fiber laser on the formation of ultracold 85Rb2 molecules is investigated as a function of its frequency (in the 1062–1070 nm range) in a magneto-optical trap. We find evidence for the formation of ground-state 85Rb2 molecules in low vibrational levels () with a maximal rate of 104 s−1, induced by short-range photoassociation by the fiber laser followed by spontaneous emission. When this laser is used to set up a dipole trap, we measure an atomic loss rate at a wavelength far from the PA resonances, only four times smaller than that observed at a PA resonance wavelength. This work may have important consequences for atom trapping using lasers around the conventional 1064 nm wavelength.

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Formation of ultracold molecules induced by a high-power single-frequency fiber laser

Henry Fernandes Passagem, Ricardo Colín‐Rodríguez, Paulo Cesar Ventura +3 more

Abstract The influence of a high-power single-frequency fiber laser on the formation of ultracold 85 Rb 2 molecules is investigated as a function of its frequency (in the 1062–1070 nm range) in a magneto-optical trap. We find evidence for the formation of ground-state 85 Rb 2 molecules in low vibrational levels ( v ≤ 20 ) with a maximal rate of 10 4 s −1 , induced by short-range photoassociation by the fiber laser followed by spontaneous emission. When this laser is used to set up a dipole trap, we measure an atomic loss rate at a wavelength far from the PA resonances, only four times smaller than that observed at a PA resonance wavelength. This work may have important consequences for atom trapping using lasers around the conventional 1064 nm wavelength.

Journal of Physics B Atomic Molecular and Optical Physics•Jan 19, 2017•7 citations

Trap loss in a rubidium crossed dipole trap by short-range photoassociation

Carlos Renato Menegatti, Bruno Marangoni, Nadia Bouloufa-Maafa +2 more

Significant two-body losses are observed in an ultracold gas of ${}^{85}$Rb or ${}^{87}$Rb atoms in a crossed dipole trap implemented with a broadband laser with a wavelength around 1071 nm. Using available spectroscopic data on the excited states of Rb${}_{2}$, as well as accurate computed transition dipole moment functions, we interpret these losses as due to photoassociation of deeply bound levels of the 0${}_{u}^{+}$ coupled states by the trapping laser, followed by spontaneous emission down to bound levels of the Rb${}_{2}$ ground state thus forming ultracold molecules. The observed ratio of 3.3 between the loss rates of ${}^{87}$Rb and ${}^{85}$Rb is well reproduced by the theoretical model.

Physical Review A•May 8, 2013•24 citations

Utlracold Rb2 Molecules: Formation, Detection and Trapping in an Optical Dipole Trap

Hyewon Pechkis

This thesis comprises two topics in the field of the ultracold atomic and molecular physics, both involving formation of ultracold 85Rb 2 by photoassociation (PA). Typically, these ground-state molecules are formed mainly in the very highest vibrational levels, rather than the low-v levels that will be required for most future investigations of ultracold molecular physics and chemistry. The first topic of my research is a method for circumventing this problem: resonant enhancement (RE) of photoassociative ground-state molecule production. The key idea of RE is to photoassociate pairs of colliding atoms into an excited state that has a bimodal vibrational probability distribution, with one peak at long range to enhance the photoassociation rate and another at shorter range to enhance radiative decay into deeply bound levels of the ground state. This can be arranged thanks to the strong spin-orbit perturbative interaction between the two 0+u states converging to two different asymptotes, (5s + 5p1/2) and (5s + 5 p3/2). This method enhances ground-state molecule formation in the region well below the dissociation limit. The experimental work described here was done at the University of Connecticut in collaboration with C. P. Koch at the Institut für Theoretische Physik, Freie Universität Berlin, Germany, who performed the theoretical analysis [1].^ The second part of my thesis is the investigation of ultracold molecules in an optical dipole trap. We have constructed a quasi-electrostratic optical trap (QUEST) for 85Rb using a focused CO2 laser [2]. This provides a very high density of ultracold atoms, up to 10 12 cm-3, providing much higher photoassociation rates. It also keeps the molecules trapped once they have formed. The QUEST provides an ample trapping lifetime for both trapped atoms and molecules, yielding about 4-5×106 atoms and about 9×105 high-v molecules. The long lifetime of the trapped molecules and atoms, combined with their high density, allows us to study interactions such as atom-molecule or molecule-molecule collisions in the ultracold regime. A preliminary experiment on Rb2 molecular decay is described. ^

•Jan 1, 2010•0 citations

Photoassociation of ultracold LiRb * molecules: Observation of high efficiency and unitarity-limited rate saturation

Sourav Dutta, John Lorenz, Adeel Altaf +2 more

We report the production of ultracold heteronuclear $^{7}\mathrm{Li}^{85}\mathrm{Rb}$ molecules in excited electronic states by photoassociation (PA) of ultracold $^{7}\mathrm{Li}$ and $^{85}\mathrm{Rb}$ atoms. PA is performed in a dual-species $^{7}\mathrm{Li}$-$^{85}\mathrm{Rb}$ magneto-optical trap (MOT) and the PA resonances are detected using trap loss spectroscopy. We identify several strong PA resonances below the Li (2$s$ ${}^{2}$${S}_{1/2}$) + Rb (5$p$ ${}^{2}{P}_{3/2}$) asymptote and experimentally determine the long range ${C}_{6}$ dispersion coefficients. We find a molecule formation rate (${P}_{\mathrm{LiRb}}$) of 3.5 \ifmmode\times\else\texttimes\fi{} 10${}^{7}$ s${}^{\ensuremath{-}1}$ and a PA rate coefficient (${K}_{\mathrm{PA}}$) of 1.3 \ifmmode\times\else\texttimes\fi{} 10${}^{\ensuremath{-}10}$ cm${}^{3}$/s, the highest among heteronuclear bi-alkali-metal molecules. At large PA laser intensity we observe the saturation of the PA rate coefficient (${K}_{\mathrm{PA}}$) close to the theoretical value at the unitarity limit.

arXiv:1311.6297•Physical Review A•Feb 19, 2014•39 citations

Continuous Loading of Ultracold Ground-State Rb285 Molecules in a Dipole Trap Using a Single Light Beam

Henry Fernandes Passagem, Ricardo Colín‐Rodríguez, Jonathan Tallant +4 more

We have developed an approach to continuously load ultracold ^{85}Rb_{2} vibrational ground-state molecules into a crossed optical dipole trap from a magneto-optical trap. The technique relies on a single high-power light beam with a broad spectrum superimposed onto a narrow peak at an energy of about 9400 cm^{-1}. This single laser source performs all the required steps: the short-range photoassociation creating ground-state molecules after radiative emission, the cooling of the molecular vibrational population down to the lowest vibrational level v_{X}=0, and the optical trapping of these molecules. Furthermore, we probe by depletion spectroscopy and determine that 75% of the v_{X}=0 ground-state molecules are in the three lowest rotational levels J_{X}=0, 1, 2. The lifetime of the ultracold molecules in the optical dipole trap is limited to about 70 ms by off-resonant light scattering. The proposed technique opens perspectives for the formation of new molecular species in the ultracold domain, which are not yet accessible by well-established approaches.

Physical Review Letters•Mar 26, 2019•9 citations

Production and Detection of Ultracold Ground State 85 Rb 133 Cs Molecules in the Lowest Vibrational Level by Short-Range Photoassociation

Yanting Zhao, Jinpeng Yuan, Zhonghao Li +3 more

We investigate the production of ultracold ground state X 1 σ + (v = 0) RbCs molecules in the lowest vibrational level via short-range photoassociation followed by spontaneous emission. The starting point is the laser cooled 85 Rb and 133 Cs atoms in a dual species, forced dark magneto-optical trap. The special intermediate level (5)0 + (v = 10) correlated to the (2) 3 π electric state is achieved by the photoassociation process. The formed ground state X 1 σ + (v = 0) molecule is resonantly excited to the 2 1 π intermediate state by a 651 nm pulse laser and is ionized by a 532 nm pulse laser and then detected by the time-of-flight mass spectrum. Saturation of the photoionization spectroscopy at large ionization laser energy is observed and the ionization efficiency is obtained from the fitting. The production of ultracold ground state 85 Rb 133 Cs molecules is facilitative for the further research about the manipulation of ultracold molecules in the rovibrational ground state.

Chinese Physics Letters•Nov 1, 2015•3 citations
The influence of a high-power single-frequency fiber laser on the formation of ultracold 85Rb2 molecules is investigated as a function of its frequency (in the 1062–1070 nm range) in a magneto-optical trap. We find evidence for the formation of ground-state 85Rb2 molecules in low vibrational levels () with a maximal rate of 104 s−1, induced by short-range photoassociation by the fiber laser followed by spontaneous emission. When this laser is used to set up a dipole trap, we measure an atomic loss rate at a wavelength far from the PA resonances, only four times smaller than that observed at a PA resonance wavelength. This work may have important consequences for atom trapping using lasers around the conventional 1064 nm wavelength.
Abstract The influence of a high-power single-frequency fiber laser on the formation of ultracold 85 Rb 2 molecules is investigated as a function of its frequency (in the 1062–1070 nm range) in a magneto-optical trap. We find evidence for the formation of ground-state 85 Rb 2 molecules in low vibrational levels ( v ≤ 20 ) with a maximal rate of 10 4 s −1 , induced by short-range photoassociation by the fiber laser followed by spontaneous emission. When this laser is used to set up a dipole trap, we measure an atomic loss rate at a wavelength far from the PA resonances, only four times smaller than that observed at a PA resonance wavelength. This work may have important consequences for atom trapping using lasers around the conventional 1064 nm wavelength.
Significant two-body losses are observed in an ultracold gas of 85{}^{85}85Rb or 87{}^{87}87Rb atoms in a crossed dipole trap implemented with a broadband laser with a wavelength around 1071 nm. Using available spectroscopic data on the excited states of Rb2{}_{2}2​, as well as accurate computed transition dipole moment functions, we interpret these losses as due to photoassociation of deeply bound levels of the 0u+{}_{u}^{+}u+​ coupled states by the trapping laser, followed by spontaneous emission down to bound levels of the Rb2{}_{2}2​ ground state thus forming ultracold molecules. The observed ratio of 3.3 between the loss rates of 87{}^{87}87Rb and 85{}^{85}85Rb is well reproduced by the theoretical model.
This thesis comprises two topics in the field of the ultracold atomic and molecular physics, both involving formation of ultracold 85Rb 2 by photoassociation (PA). Typically, these ground-state molecules are formed mainly in the very highest vibrational levels, rather than the low-v levels that will be required for most future investigations of ultracold molecular physics and chemistry. The first topic of my research is a method for circumventing this problem: resonant enhancement (RE) of photoassociative ground-state molecule production. The key idea of RE is to photoassociate pairs of colliding atoms into an excited state that has a bimodal vibrational probability distribution, with one peak at long range to enhance the photoassociation rate and another at shorter range to enhance radiative decay into deeply bound levels of the ground state. This can be arranged thanks to the strong spin-orbit perturbative interaction between the two 0+u states converging to two different asymptotes, (5s + 5p1/2) and (5s + 5 p3/2). This method enhances ground-state molecule formation in the region well below the dissociation limit. The experimental work described here was done at the University of Connecticut in collaboration with C. P. Koch at the Institut für Theoretische Physik, Freie Universität Berlin, Germany, who performed the theoretical analysis [1].^ The second part of my thesis is the investigation of ultracold molecules in an optical dipole trap. We have constructed a quasi-electrostratic optical trap (QUEST) for 85Rb using a focused CO2 laser [2]. This provides a very high density of ultracold atoms, up to 10 12 cm-3, providing much higher photoassociation rates. It also keeps the molecules trapped once they have formed. The QUEST provides an ample trapping lifetime for both trapped atoms and molecules, yielding about 4-5×106 atoms and about 9×105 high-v molecules. The long lifetime of the trapped molecules and atoms, combined with their high density, allows us to study interactions such as atom-molecule or molecule-molecule collisions in the ultracold regime. A preliminary experiment on Rb2 molecular decay is described. ^
We report the production of ultracold heteronuclear 7Li85Rb^{7}\mathrm{Li}^{85}\mathrm{Rb}7Li85Rb molecules in excited electronic states by photoassociation (PA) of ultracold 7Li^{7}\mathrm{Li}7Li and 85Rb^{85}\mathrm{Rb}85Rb atoms. PA is performed in a dual-species 7Li^{7}\mathrm{Li}7Li-85Rb^{85}\mathrm{Rb}85Rb magneto-optical trap (MOT) and the PA resonances are detected using trap loss spectroscopy. We identify several strong PA resonances below the Li (2sss 2{}^{2}2S1/2{S}_{1/2}S1/2​) + Rb (5ppp 2P3/2{}^{2}{P}_{3/2}2P3/2​) asymptote and experimentally determine the long range C6{C}_{6}C6​ dispersion coefficients. We find a molecule formation rate (PLiRb{P}_{\mathrm{LiRb}}PLiRb​) of 3.5 \ifmmode\times\else\texttimes\fi{} 107{}^{7}7 s${}^{\ensuremath{-}1}$ and a PA rate coefficient (KPA{K}_{\mathrm{PA}}KPA​) of 1.3 \ifmmode\times\else\texttimes\fi{} 10${}^{\ensuremath{-}10}$ cm3{}^{3}3/s, the highest among heteronuclear bi-alkali-metal molecules. At large PA laser intensity we observe the saturation of the PA rate coefficient (KPA{K}_{\mathrm{PA}}KPA​) close to the theoretical value at the unitarity limit.
We have developed an approach to continuously load ultracold ^{85}Rb_{2} vibrational ground-state molecules into a crossed optical dipole trap from a magneto-optical trap. The technique relies on a single high-power light beam with a broad spectrum superimposed onto a narrow peak at an energy of about 9400 cm^{-1}. This single laser source performs all the required steps: the short-range photoassociation creating ground-state molecules after radiative emission, the cooling of the molecular vibrational population down to the lowest vibrational level v_{X}=0, and the optical trapping of these molecules. Furthermore, we probe by depletion spectroscopy and determine that 75% of the v_{X}=0 ground-state molecules are in the three lowest rotational levels J_{X}=0, 1, 2. The lifetime of the ultracold molecules in the optical dipole trap is limited to about 70 ms by off-resonant light scattering. The proposed technique opens perspectives for the formation of new molecular species in the ultracold domain, which are not yet accessible by well-established approaches.
We investigate the production of ultracold ground state X 1 σ + (v = 0) RbCs molecules in the lowest vibrational level via short-range photoassociation followed by spontaneous emission. The starting point is the laser cooled 85 Rb and 133 Cs atoms in a dual species, forced dark magneto-optical trap. The special intermediate level (5)0 + (v = 10) correlated to the (2) 3 π electric state is achieved by the photoassociation process. The formed ground state X 1 σ + (v = 0) molecule is resonantly excited to the 2 1 π intermediate state by a 651 nm pulse laser and is ionized by a 532 nm pulse laser and then detected by the time-of-flight mass spectrum. Saturation of the photoionization spectroscopy at large ionization laser energy is observed and the ionization efficiency is obtained from the fitting. The production of ultracold ground state 85 Rb 133 Cs molecules is facilitative for the further research about the manipulation of ultracold molecules in the rovibrational ground state.