Cold and dense samples of naphthalene (C(10)H(8)) are produced using buffer gas cooling in combination with rapid, high flow molecule injection. The observed naphthalene density is n approximately 10(11) cm(-3) over a volume of a few cm(3) at a temperature of 6 K. We observe naphthalene-naphthalene collisions through two-body loss of naphthalene with a loss cross section of sigma(N-N) = 1.4 x 10(-14) cm(2). Analysis is presented that indicates that this combination of techniques will be applicable to many comparably sized molecules. This technique can also be combined with cryogenic beam methods(1) to produce cold, high flux, continuous molecular beams.
Cold and dense samples of naphthalene (C(10)H(8)) are produced using buffer gas cooling in combination with rapid, high flow molecule injection. The observed naphthalene density is n approximately 10(11) cm(-3) over a volume of a few cm(3) at a temperature of 6 K. We observe naphthalene-naphthalene collisions through two-body loss of naphthalene with a loss cross section of sigma(N-N) = 1.4 x 10(-14) cm(2). Analysis is presented that indicates that this combination of techniques will be applicable to many comparably sized molecules. This technique can also be combined with cryogenic beam methods(1) to produce cold, high flux, continuous molecular beams.
We reported a detailed experimental study of the cold collision of barium monofluoride (BaF) with buffer gas and the high-resolution spectroscopy relevant with direct laser cooling. BaF molecules are efficiently produced with laser ablation and buffer-gas cooled in a cryogenic apparatus. The laser cooling relevant transition $|X\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{\ensuremath{\Sigma}},v=0,N=1\ensuremath{\rangle}$ to $|A\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{\ensuremath{\Pi}},{v}^{\ensuremath{'}}=0,{J}^{\ensuremath{'}}=1/2\ensuremath{\rangle}$ is identified. The collision cross section with buffer gas is measured to be $1.4(7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\phantom{\rule{4.pt}{0ex}}{\text{cm}}^{\ensuremath{-}2}$, which is very suitable for buffer-gas cooling. Both rotational and vibrational temperatures are effectively cooled, and a large amount of molecules are quenched into the desired states. Our study provides an important benchmark for further laser cooling of the BaF molecule.
We introduce a method for classical trajectory calculations to simulate collisions between atoms and large rigid asymmetric-top molecules. We investigate the formation of molecule-helium complexes in buffer-gas cooling experiments at a temperature of 6.5 K for molecules as large as naphthalene. Our calculations show that the mean lifetime of the naphthalene-helium quasi-bound collision complex is not long enough for the formation of stable clusters under the experimental conditions. Our results suggest that it may be possible to improve the efficiency of the production of cold molecules in buffer-gas cooling experiments by increasing the density of helium. In addition, we find that the shape of molecules is important for the collision dynamics when the vibrational motion of molecules is frozen. For some molecules, it is even more crucial than the number of accessible degrees of freedom. This indicates that by selecting molecules with suitable shape for buffer-gas cooling, it may be possible to cool molecules with a very large number of degrees of freedom.
We realize a continuous, intense, cold molecular and atomic beam source based on buffer-gas cooling. Hot vapor (up to 600 K) from an oven is mixed with cold (15 K) neon buffer gas, and then emitted into a high-flux beam. The novel use of cold neon as a buffer gas produces a forward velocity distribution and low-energy tail that is comparable to much colder helium-based sources. We expect this source to be trivially generalizable to a very wide range of atomic and molecular species with significant vapor pressure below 1000 K. The source has properties that make it a good starting point for laser cooling of molecules or atoms, cold collision studies, trapping, or nonlinear optics in buffer-gas-cooled atomic or molecular gases. A continuous guided beam of cold deuterated ammonia with a flux of 3×10\\(^{11}\\) ND\\(_{3}\\) molecules s\\(^{−1}\\) and a continuous free-space beam of cold potassium with a flux of 1×10\\(^{16}\\) K atoms s\\(^{−1}\\) are realized.
We realize a continuous, intense, cold molecular and atomic beam source based on buffer-gas cooling. Hot vapor (up to 600 K) from an oven is mixed with cold (15 K) neon buffer gas, and then emitted into a high-flux beam. The novel use of cold neon as a buffer gas produces a forward velocity distribution and low-energy tail that is comparable to much colder helium-based sources. We expect this source to be trivially generalizable to a very wide range of atomic and molecular species with significant vapor pressure below 1000 K. The source has properties that make it a good starting point for laser cooling of molecules or atoms, cold collision studies, trapping, or nonlinear optics in buffer-gas-cooled atomic or molecular gases. A continuous guided beam of cold deuterated ammonia with a flux of 3 × 10 11 ND 3 molecules s −1 and a continuous free-space beam of cold potassium with a flux of 1 × 10 16 K atoms s −1 are realized.
Cryogenically cooled buffer gas beam sources of the molecule thorium monoxide (ThO) are optimized and characterized. Both helium and neon buffer gas sources are shown to produce ThO beams with high flux, low divergence, low forward velocity, and cold internal temperature for a variety of stagnation densities and nozzle diameters. The beam operates with a buffer gas stagnation density of ∼10(15)-10(16) cm(-3) (Reynolds number ∼1-100), resulting in expansion cooling of the internal temperature of the ThO to as low as 2 K. For the neon (helium) based source, this represents cooling by a factor of about 10 (2) from the initial nozzle temperature of about 20 K (4 K). These sources deliver ∼10(11) ThO molecules in a single quantum state within a 1-3 ms long pulse at 10 Hz repetition rate. Under conditions optimized for a future precision spectroscopy application [A. C. Vutha et al., J. Phys. B: At., Mol. Opt. Phys., 2010, 43, 074007], the neon-based beam has the following characteristics: forward velocity of 170 m s(-1), internal temperature of 3.4 K, and brightness of 3 × 10(11) ground state molecules per steradian per pulse. Compared to typical supersonic sources, the relatively low stagnation density of this source and the fact that the cooling mechanism relies only on collisions with an inert buffer gas make it widely applicable to many atomic and molecular species, including those which are chemically reactive, such as ThO.
Cryogenically cooled buffer gas beam sources of the molecule thorium monoxide (ThO) are optimized and characterized. Both helium and neon buffer gas sources are shown to produce ThO beams with high flux, low divergence, low forward velocity, and cold internal temperature for a variety of stagnation densities and nozzle diameters. The beam operates with a buffer gas stagnation density of \\(\\sim 10^{15}-10^{16}\\) cm\\(^{-3}\\) (Reynolds number \\(\\sim 1-100\\)), resulting in expansion cooling of the internal temperature of the ThO to as low as 2 K. For the neon (helium) based source, this represents cooling by a factor of about 10 (2) from the initial nozzle temperature of about 20 K (4 K). These sources deliver \\(\\sim 10^{11}\\) ThO molecules in a single quantum state within a 1-3 ms long pulse at 10 Hz repetition rate. Under conditions optimized for a future precision spectroscopy application [A C Vutha et al 2010 J. Phys. B: At. Mol. Opt. Phys. 43 074007], the neon-based beam has the following characteristics: forward velocity of 170 m/s, internal temperature of 3.4 K, and brightness of \\(3 \\times 10^{11}\\) ground state molecules per steradian per pulse. Compared to typical supersonic sources, the relatively low stagnation density of this source, and the fact that the cooling mechanism relies only on collisions with an inert buffer gas, make it widely applicable to many atomic and molecular species, including those which are chemically reactive, such as ThO.