Buffer gas cooled atoms and molecules: Production, collisional studies, and applications

We propose a method to study the rotational relaxation of polar molecules [here taking fluoromethane $({\mathrm{CH}}_{3}\mathrm{F})$ as an example] in collisions with 3.5 K buffer-gas helium (He) atoms by using an electrostatic guiding technique. The dependence of the guiding signal of ${\mathrm{CH}}_{3}\mathrm{F}$ on the injected He flux and the dependence of the guiding efficiency of ${\mathrm{CH}}_{3}\mathrm{F}$ on its rotational temperature are investigated both theoretically and experimentally. By comparing the experimental and simulated results, we find that the translational and rotational temperatures of the buffer-gas cooled ${\mathrm{CH}}_{3}\mathrm{F}$ molecules can reach to about 5.48 and 0.60 K, respectively, and the ratio between the translational and average rotational collisional cross sections of ${\mathrm{CH}}_{3}\mathrm{F}\ensuremath{-}\mathrm{He}$ is $\ensuremath{\gamma}={\ensuremath{\sigma}}_{t}/{\ensuremath{\sigma}}_{r}=36.49\ifmmode\pm\else\textpm\fi{}6.15$. In addition, the slowing, cooling, and boosting effects of the molecular beam with different injected He fluxes are also observed and their forming conditions are investigated in some detail. Our study shows that our proposed method can not only be used to measure the translational and rotational temperatures of the buffer-gas cooled molecules, but also to measure the ratio of the translational collisional cross section to the average rotational collisional cross section, and even to measure the average rotational collisional cross section when the translational collisional cross section is measured by fitting the lifetime of molecule signal to get a numerical solution from the diffusion equation of buffer-gas He atoms in the cell.We propose a method to study the rotational relaxation of polar molecules [here taking fluoromethane $({\mathrm{CH}}_{3}\mathrm{F})$ as an example] in collisions with 3.5 K buffer-gas helium (He) atoms by using an electrostatic guiding technique. The dependence of the guiding signal of ${\mathrm{CH}}_{3}\mathrm{F}$ on the injected He flux and the dependence of the guiding efficiency of ${\mathrm{CH}}_{3}\mathrm{F}$ on its rotational temperature are investigated both theoretically and experimentally. By comparing the experimental and simulated results, we find that the translational and rotational temperatures of the buffer-gas cooled ${\mathrm{CH}}_{3}\mathrm{F}$ molecules can reach to about 5.48 and 0.60 K, respectively, and the ratio between the translational and average rotational collisional cross sections of ${\mathrm{CH}}_{3}\mathrm{F}\ensuremath{-}\mathrm{He}$ is $\ensuremath{\gamma}={\ensuremath{\sigma}}_{t}/{\ensuremath{\sigma}}_{r}=36.49\ifmmode\pm\else\textpm\fi{}6.15$. In addition, the slowing, cooling, and boosting effects of the molecular beam with different injected He fluxes are also observed and their forming conditions are investigated in some detail. Our study shows that our proposed method can not only be used to measure the translational and rotational temperatures of the buffer-gas cooled molecules, but also to measure the ratio of the translational collisional cross section to the average rotational collisional cross section, and even to measure the average rotational collisional cross section when the translational collisional cross section is measured by fitting the lifetime of molecule signal to get a numerical solution from the diffusion equation of buffer-gas He atoms in the cell.

Physical Review AJun 6, 20169 citations

Buffer-gas cooling of diatomic molecules

Dimitri Michael Egorov

Jan 1, 20046 citations

Buffer gas cooled beams and cold molecular collisions

David Patterson

Jan 1, 20103 citations

Realization of coherent optically dense media via buffer-gas cooling

Tao Hong, Alexey Vyacheslavovich Gorshkov, David Patterson +4 more

We demonstrate that buffer-gas cooling combined with laser ablation can be used to create coherent optical media with high optical depth and low Doppler broadening that offers metastable states with low collisional and motional decoherence. Demonstration of this generic technique opens pathways to coherent optics with a large variety of atoms and molecules. We use helium buffer gas to cool $^{87}\mathrm{Rb}$ atoms to below $7\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and slow atom diffusion to the walls. Electromagnetically induced transparency in this medium allows for 50% transmission in a medium with initial optical depth $D>70$ and for slow pulse propagation with large delay-bandwidth products. In the high- $D$ regime, we observe high-contrast spectrum oscillations due to efficient four-wave mixing.We demonstrate that buffer-gas cooling combined with laser ablation can be used to create coherent optical media with high optical depth and low Doppler broadening that offers metastable states with low collisional and motional decoherence. Demonstration of this generic technique opens pathways to coherent optics with a large variety of atoms and molecules. We use helium buffer gas to cool $^{87}\mathrm{Rb}$ atoms to below $7\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and slow atom diffusion to the walls. Electromagnetically induced transparency in this medium allows for 50% transmission in a medium with initial optical depth $D>70$ and for slow pulse propagation with large delay-bandwidth products. In the high-$D$ regime, we observe high-contrast spectrum oscillations due to efficient four-wave mixing.

arXiv:0805.1416Physical Review AJan 6, 200927 citations

The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules

Nicholas R. Hutzler, Hsin-I Lu, John M. Doyle

Beams of atoms and molecules are stalwart tools for spectroscopy and studies of collisional processes. The supersonic expansion technique can create cold beams of many species of atoms and molecules. However, the resulting beam is typically moving at a speed of 300-600 m/s in the lab frame, and for a large class of species has insufficient flux (i.e. brightness) for important applications. In contrast, buffer gas beams can be a superior method in many cases, producing cold and relatively slow molecules in the lab frame with high brightness and great versatility. There are basic differences between supersonic and buffer gas cooled beams regarding particular technological advantages and constraints. At present, it is clear that not all of the possible variations on the buffer gas method have been studied. In this review, we will present a survey of the current state of the art in buffer gas beams, and explore some of the possible future directions that these new methods might take.Beams of atoms and molecules are stalwart tools for spectroscopy and studies of collisional processes. The supersonic expansion technique can create cold beams of many species of atoms and molecules. However, the resulting beam is typically moving at a speed of 300-600 m/s in the lab frame, and for a large class of species has insufficient flux (i.e. brightness) for important applications. In contrast, buffer gas beams can be a superior method in many cases, producing cold and relatively slow molecules in the lab frame with high brightness and great versatility. There are basic differences between supersonic and buffer gas cooled beams regarding particular technological advantages and constraints. At present, it is clear that not all of the possible variations on the buffer gas method have been studied. In this review, we will present a survey of the current state of the art in buffer gas beams, and explore some of the possible future directions that these new methods might take.

arXiv:1111.2841Chemical ReviewsMay 9, 2012381 citations

We propose a method to study the rotational relaxation of polar molecules [here taking fluoromethane

({\mathrm{CH}}_{3}\mathrm{F})

as an example] in collisions with 3.5 K buffer-gas helium (He) atoms by using an electrostatic guiding technique. The dependence of the guiding signal of

{\mathrm{CH}}_{3}\mathrm{F}

on the injected He flux and the dependence of the guiding efficiency of

{\mathrm{CH}}_{3}\mathrm{F}

on its rotational temperature are investigated both theoretically and experimentally. By comparing the experimental and simulated results, we find that the translational and rotational temperatures of the buffer-gas cooled

{\mathrm{CH}}_{3}\mathrm{F}

molecules can reach to about 5.48 and 0.60 K, respectively, and the ratio between the translational and average rotational collisional cross sections of ${\mathrm{CH}}_{3}\mathrm{F}\ensuremath{-}\mathrm{He}$ is $\ensuremath{\gamma}={\ensuremath{\sigma}}_{t}/{\ensuremath{\sigma}}_{r}=36.49\ifmmode\pm\else\textpm\fi{}6.15$. In addition, the slowing, cooling, and boosting effects of the molecular beam with different injected He fluxes are also observed and their forming conditions are investigated in some detail. Our study shows that our proposed method can not only be used to measure the translational and rotational temperatures of the buffer-gas cooled molecules, but also to measure the ratio of the translational collisional cross section to the average rotational collisional cross section, and even to measure the average rotational collisional cross section when the translational collisional cross section is measured by fitting the lifetime of molecule signal to get a numerical solution from the diffusion equation of buffer-gas He atoms in the cell.

^{87}\mathrm{Rb}

atoms to below

7\phantom{\rule{0.3em}{0ex}}\mathrm{K}

and slow atom diffusion to the walls. Electromagnetically induced transparency in this medium allows for 50% transmission in a medium with initial optical depth

D>70

and for slow pulse propagation with large delay-bandwidth products. In the high-

D

regime, we observe high-contrast spectrum oscillations due to efficient four-wave mixing.