The Temperature of Atoms in a Magneto-optical Trap

Abstract

A cloud of ultracold atoms confined in a magneto-optical trap (MOT) has a temperature greater than that of a low-density vapour in the same light field. It has been observed (Drewsen M. et al., AppL Phys. B, 59 (1994) 283) that this temperature excess is proportional to the cube root of the total number of trapped atoms (N1/3). We present an explanation for this effect in terms of the scattering which arises when photons spontaneously emitted by atoms have an appreciable probability of being reabsorbed within the cloud. This hypothesis has been tested by time-of-flight measurements of the temperature of clouds of atoms released from a MOT into l-dimensional and 3-dimensional optical molasses in the g + -r -and lin I lin configuration.

Extra-heating mechanism in Doppler cooling experiments

“…They essentially rely on reabsorption of scattered photons in the cold MOT [13]. This situation is encountered as soon as light multiple scattering sets in, i.e.…”

Absorption spectroscopy of trapped rubidium atoms

“…We note that the fit is indistinguishable from the Lorentzian described by (11) and suggests that the technique is suitable for a precision measurement of the natural line width. We also note that the precision measurement would involve fits to the closed form solutions of the Voigt profile described by (14). 8.078 0.028 Figure 5 shows the effect of varying the probe beam power on the line width of the absorption line shape.…”

“…Atom traps have also been used to improve the accuracy of atomic clocks [11] and study cold collisions [12]. For many of these applications, it is necessary to understand the scaling laws that govern the density distribution and temperature of cold atoms [13,14]. This involves the use of reliable diagnostic techniques such as the determination of the number of atoms by fluorescence detection using a photomultiplier tube (PMT) [15], cloud size and temperature using charge-coupled devices (CCD) [16,17], and density using absorption spectroscopy [18].…”

“…Equation (14) can be expressed in closed form by performing a Taylor expansion of the integrand if the optical depth of the sample is small. This allows the absorption spectrum to be fit to a Voigt profile, if the Doppler contribution is known.…”

Measurement of temperature of laser cooled atoms by one-dimensional expansion in a magneto-optical trap

“…Of many attributes of the cold atomic clouds formed in a magnetooptical trap ͑MOT͒, temperature is perhaps the most important one and there exist a number of techniques developed for its measurement. These include release and recapture 1 ͑R&R͒ and time of flight [2][3][4][5] ͑TOF͒ techniques, and also other more elaborate methods based on forced oscillation of the cloud, 6 fluorescence spectrum analysis, 7 recoil induced resonances, 8 and four wave mixing. 9 A direct method, 10,11 which is an extension of the TOF technique, is used to allow the cold cloud to expand ballistically after abruptly switching off the trapping fields and follow its spatiotemporal evolution by absorption or fluorescence imaging technique with the help of a probe laser beam.…”