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Conference on Precision Electromagnetic Measurements

Population relaxation of Cs atoms in MOT [frequency standard applications]

Atsushi Hasegawa, Kentaro Fukuda, T. Suzuki, Takayoshi Kobayashi, M. Tachikawa, Mizuhiko Hosokawa

Published Jun 25, 2003• 0 citations
Publisher

Abstract

The dynamical behavior of magneto-optically trapped (MOT) Cs atoms is studied by a laser-spectroscopic method. Atoms in the region irradiated by a pulsed laser beam are ejected from the MOT. Recovery of the local population appears in the absorption signals of a probe laser while total population is observed as a fluorescence signal. Anomalously large absorption is observed just after the pulse irradiation.

DOI
10.1109/cpem.2002.1034921

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The dynamical behavior of magneto-optically trapped (MOT) Cs atoms is studied by a laser-spectroscopic method. Atoms in the region irradiated by a pulsed laser beam are ejected from the MOT. Recovery of the local population appears in the absorption signals of a probe laser while total population is observed as a fluorescence signal. Anomalously large absorption is observed just after the pulse irradiation.
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Investigations of optical processes for laser cooled and trapped atoms are described. Fluorescence from Cs atoms in a magneto-optical trap is detected under conditions of very low atomic density. Discrete steps are observed in the fluorescent signal versus time and are associated with the arrival and departure of individual trapped atoms. Histograms of the frequency of occurrence of a given level of fluorescence exhibit a series of uniformly spaced peaks that are attributed to the presence of N = 0, 1, 2 atoms in the trap. In addition, numerical absorption and emission spectra for three-level [...], [...], and V systems under intense radiations are calculated. Absorption spectra for a [...] system is used to explain the probe-wave amplification and absorption spectra recorded for Cs atoms cooled and confined in a magneto-optical trap, in which novel spectral features of narrow frequency widths with single-pass gain exceeding 20% are observed. The consequence of the optical gain is demonstrated to lead to negative radiation pressure, which is investigated together with other mechanical forces in the trap. Various alternative trapping schemes in three-level and two-level atoms are proposed as possible means to compress an atomic sample and demonstrated for a two-level magneto-optical trap.
A Cs-133 Magneto-Optical Trap (MOT) has been developed at the Time and Frequency Division of the Centro Nacional de Metrolog´ CENAM, in Mexico. This MOT is part of a primary frequency standard based on ultra-cold Cs atoms, called CsF-1 clock, under development at CENAM. In this Cs MOT, we use the standard configuration (ae + i ae i ) 4-horizontal 2-vertical laser beams 1.9 cm in diameter, with 5 mW each. We use a 852 nm, 5 mW, DBR laser as a master laser which is stabilized by saturation spectroscopy. Emission linewidth of the master laser is 1 MHz. In order to amplify the light of the master laser, a 50 mW, 852 nm AlGaAs laser is used as slave laser. This slave laser is stabilized by light injection technique. A 12 MHz red shift of the light is performed by two double passes through two Acusto-Optic Modulators (AOMs). The optical part of the CENAMs MOT is very robust against mechanical vibration, acoustic noise and temperature changes in our laboratory, because none of our diode lasers use an extended cavity to reduce the linewidth. In this paper, we report results of our MOT characterization as a function of several operation parameters such as the intensity of laser beams, the laser beam diameter, the red shift of light, and the gradient of the magnetic field. We also report accurate absolute measurement of the number of Cs atoms trapped in our Cs MOT. We found up to6 £ 10 7 Cs atoms trapped in our MOT measured with an uncertainty no greater than 6.4%.
Subnatural linewidth in an optical transition in Cs was obtained by the suppression and recovery of the trapping of atoms. Cold Cs atoms in a magneto-optical trap (MOT) were irradiated using a weak probe laser to suppress MOT loading. When a counterpropagating coupling laser was directed to be resonant with the upper transition, the probe laser was induced to transmit and the MOT loading was recovered. This work investigates quantitatively this behavior by applying simulated electromagnetically induced transparency, taking into account the linewidth of the lasers as a decoherence source.
A two-color magneto-optical trap (MOT) for trapping cesium (Cs) atoms is experimentally realized. This two-color MOT employs the radiation forces due to photon scattering from the Cs 6P(3/2) F' = 5 - 8S(1/2) F" = 4 excited-state transition, which replaced one pair of the three pairs of cooling/trapping laser beams operating on a single-photon red detuning to the Cs 6S(1/2) F = 4 - 6P(3/2) F' = 5 cycling transition in a standard six-beam Cs MOT, and can cool and trap atoms on both the red-detuning and blue-detuning sides of the two-photon resonance. Employing the two-color MOT, the background-free fluorescence detection of trapped atoms has been demonstrated. This technique will be useful for observation of weak fluorescence signal radiated from single atoms in MOT.