We present measurements and calculations of the trap loss rate for laser cooled Rb atoms confined in either a magneto-optic or a magnetic quadrupole trap when exposed to a room temperature background gas of Ar. We study the loss rate as a function of trap depth and find that copious glancing elastic collisions, which occur in the so-called quantum-diffractive regime and impart very little energy to the trapped atoms, result in significant differences in the loss rate for the MOT compared to a pure magnetic trap due solely to the difference in potential depth. This finding highlights the importance of knowing the trap depth when attempting to infer the total collision cross section from measurements of trap loss rates. Moreover, this variation of trap loss rate with trap depth can be used to extract information about the differential cross section.Comment: 9 pages, 9 figure

We present a method for determining the depth of an atomic or molecular trap of any type. This method relies on a measurement of the trap loss rate induced by collisions with background gas particles. Given a fixed gas composition, the loss rate uniquely determines the trap depth. Because of the "soft" long-range nature of the van der Waals interaction, these collisions transfer kinetic energy to trapped particles across a broad range of energy scales, from room temperature to the microkelvin energy scale. The resulting loss rate therefore exhibits a significant variation over an enormous range of trap depths, making this technique a powerful diagnostic with a large dynamic range. We present trap depth measurements of a Rb magneto-optical trap using this method and a different technique that relies on measurements of loss rates during optical excitation of colliding atoms to a repulsive molecular state. The main advantage of the method presented here is its large dynamic range and applicability to traps of any type requiring only knowledge of the background gas density and the interaction potential between the trapped and background gas particles.The particle loss rate from a trap is one of the primary observables for probing the collisional physics of trapped gases. Measurements of trap loss are routinely made in a variety of experiments to deduce elastic and inelastic collision cross sections for intratrap collisions and for collisions between trapped species and externally introduced particles. Trap depth often plays an important role in the interpretation of these measurements. A well-studied example of this is the large intensity-dependent variation displayed by the two-body intratrap loss-rate coefficient for atoms trapped in a magnetooptical trap (MOT). This variation results from an interplay of trap depth and the energy imparted to trapped atoms due to hyperfine or fine structure changing collisions, as well as radiative escape [1][2][3][4][5][6][7][8][9][10][11][12]. More recently, inelastic and elastic collision rates in dipole traps have been of interest, particularly for metastable species [13,14]. The fraction of elastic collisions resulting in an evaporated atom depends on trap depth, which is a key parameter for evaporative cooling [13,15,16]. The lifetime dependence of a state-insenstive dipole trap on trap depth for cesium atoms has also recently been investigated [17]. Of course the most fundamental role of trap depth is that it be large enough to provide sufficient confinement, which has been an issue for experiments with buffer-gas-cooled atoms or molecules [18,19].In recent years there has been interest in making precision determinations of collision cross-sections from measurements of particle loss rates due to externally introduced particles. These measurements involve collisions of trapped neutral particles with neutral atoms and molecules [20][21][22][23][24], electron beams [25][26][27], and trapped ions [28][29][30]. Photoionization cross sections have also been investigated though mea...

This paper describes a semi-quantitative method, suitable for a student laboratory exercise that shows that the acoustic properties of the soundbox of a musical instrument depend on the sound speed of the atmosphere surrounding and filling the instrument. A gas tent was constructed and used to enclose instruments in helium, carbon dioxide and mixtures thereof, allowing the sound speed to be varied from 250 to 1000 m/s. Soundboard admittance data were taken using a guitar and a violin as examples. The data, expressed as contour plots, show clearly the qualitative relationship between air and wood modes, and the guitar data are compared with a simple mechanical model. Experimental details of the construction and operation of gas tent are given, with attention paid to safety issues.