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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Laser cooling and trapping of Cs-133 neutral atoms at CENAM

M. Talavera-Ortega, J. M. López Romero, E. de Carlos López

Published Feb 13, 2006• 0 citations

Abstract

At the moment the National Center of Metrology (CENAM) develops to the necessary technology for the creation of a frequency standard of high accuracy denominated CsF1 atomic fountain. The first stage of development of this clock consists of laser cooling and trapping neutral Cs-133 atoms. The mechanism of laser cooling and trapping of atoms requires of the accomplishment of a magneto-optical trap (MOT) in where is indispensable to maintain a strict control in its parameters of operation. In this experiment, the MOT operates with three set of red detuning |62s1/2, F=4|-> |62s3/2, F'=5| cyclical transition of Cs-133, mutually orthogonal, counterpropagating laser beams, with opposite circular polarization, intersecting at the center of a magnetic field which is generated by a pair of coil in anti-Helmholtz configuration. Additionally, a beam of light that comes from a repumping laser, tuned to the frequency of the |62s1/2, F=3|->|62s3/2, F'=4| transition of Cs-133, is injected to the MOT to maintain an atoms population in the |62s1/2, F=4| state. To cool and trap atoms to so low temperatures, of the order of the microkelvins on the zero absolute, by several seconds, minutes or even by several hours, provided the fundamentals tools to us to study the temporal and spatial behavior of the fluorescence of the atomic cloud and to make exact measurements in the count of such, in order to deduce the parameters of operation of the MOT that allows us to trap 1010 atoms or more. In this work the theoretical concepts as well as the experimental details of the parameters of operation of the MOT for the formation of the cold atom cloud are approached.

DOI: 10.1117/12.674615

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At the moment the National Center of Metrology (CENAM) develops to the necessary technology for the creation of a frequency standard of high accuracy denominated CsF1 atomic fountain. The first stage of development of this clock consists of laser cooling and trapping neutral Cs-133 atoms. The mechanism of laser cooling and trapping of atoms requires of the accomplishment of a magneto-optical trap (MOT) in where is indispensable to maintain a strict control in its parameters of operation. In this experiment, the MOT operates with three set of red detuning |62s1/2, F=4|-> |62s3/2, F'=5| cyclical transition of Cs-133, mutually orthogonal, counterpropagating laser beams, with opposite circular polarization, intersecting at the center of a magnetic field which is generated by a pair of coil in anti-Helmholtz configuration. Additionally, a beam of light that comes from a repumping laser, tuned to the frequency of the |62s1/2, F=3|->|62s3/2, F'=4| transition of Cs-133, is injected to the MOT to maintain an atoms population in the |62s1/2, F=4| state. To cool and trap atoms to so low temperatures, of the order of the microkelvins on the zero absolute, by several seconds, minutes or even by several hours, provided the fundamentals tools to us to study the temporal and spatial behavior of the fluorescence of the atomic cloud and to make exact measurements in the count of such, in order to deduce the parameters of operation of the MOT that allows us to trap 1010 atoms or more. In this work the theoretical concepts as well as the experimental details of the parameters of operation of the MOT for the formation of the cold atom cloud are approached.

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%.

The accelerated development of laser methods for manipulating the internal state and motion of atoms, and the recent primary evaluation in France of a cesium frequency standard using cold atoms in an atomic fountain configuration, allow the frontiers of time metrology, accuracy, and stability to be pushed near parts in the 1016 level, a factor of 100 over the present primary laboratory clocks. These positive results revived the development of more accurate cesium atomic clocks, and the Institute of National Measurement Standards (INMS), of the National Research Council of Canada (NRC) is undertaking a cesium-fountain project aimed at reaching these new levels of accuracy and stability. This paper reviews its present status. To appreciate the considerable impact of cold atoms in time and frequency metrology, we begin by recalling the background principles of traditional cesium frequency standards, their typical performance and main limitations. After introducing the important theoretical results essential to understanding the techniques of laser cooling and magneto-optical trapping, we focus on describing the characterization and control of our magneto-optical trap (MOT) and report the parameters that allow us to fill the trap with a few million atoms in less than a second and cool them to a temperature lower than 5 muK using optical molasses. We will describe the specifics of our cesium-fountain prototype, which operates with a 2-dimensional moving molasses. This special configuration is applicable for multipulse operation of the fountain, which can greatly relax the local oscillator requirements for time keeping. Finally, progress toward our objective of launching cooled atoms, at a rate of one ensemble per second, at speeds of 7 m/s, for a fountain with an interrogation time of about 1 s, will be analysed.PACS Nos.: 06.20, 06.30, and 32.80P

The magneto-optical trap (MOT) serves as the culmination of optical cooling and trapping, where by applying a linear magnetic field to orthogonal, circularly polarized, retroreflecting laser beams, one can produce a dense cloud of very cold atoms, on the order of μK. This work set out to create a magneto-optical trap using only visible light with the 6s 2S1/2 → 7p 2P◦ 3/2 transition of cesium-133, which is far weaker than the transition typically employed for a cesium-133 MOT. This transition alone has yet to be used in isolation to create a MOT, and the purpose of this work is to demonstrate the feasibility of such a MOT. While the creation of a MOT with the setup produced has thus far been unsuccessful, the components are in place for one to be made as a demonstration of optical cooling and trapping that should be visible to the naked eye. Additionally, an experimental setup was created for high precision measurements of the absolute energies of the 7p 2P◦ 1/2 and 7p 2P◦ 3/2 states. The theory behind the MOT and high precision spectroscopy is expounded upon within.

The results of characterization of cold cloud of cesium (Cs) atoms trapped in a magneto-optical trap (MOT) have been presented. The MOT is a part of the Physics package of the Cs Fountain Clock being developed at National Physical Laboratory (NPL), India. The number of atoms, size and temperature of the cloud have been measured and calculated. It is also been investigated how the number of trapped atoms changes with the trapping laser’s beam intensity, detuning and magnetic-field gradient of the trap.

Present status of laser cooling experiments in NRLM is presented. Laser cooling and trapping experiments for cesium atoms are continued in NRLM to develop an atomic fountain frequency standard. As a first step, we performed Cs atomic beam deceleration and trapping experiments. Atomic beam cesium atoms were decelerated by counterpropagating radiation from semiconductor laser diodes. The laser frequency was chirped to keep it in resonance with the decelerated atoms. The decelerated atoms were trapped by six mutually orthogonal laser beams in a magneto-optical trap configuration. The atoms could also be trapped directly from ambient cesium gas in a glass cell without using the deceleration laser beam. The characteristics of the trapped atoms are reported.

Magneto-optical traps (MOTs) are a workhorse technology for neutral-atom quantum sensing, simulation, and computing. Here, we demonstrate a MOT optimized for inertial quantum sensing and precision metrology applications. Our MOT traps

4\times10^8

cesium (Cs) atoms in a robust, modular system that achieves stable operation through two design features: (1) we use divergent cooling laser beams to reduce unwanted reflections and (2) optical elements are mounted in a fiber-coupled, compact, and modular cage rigidly attached to the vacuum chamber. Following polarization-gradient cooling (PGC), the system produces atom samples with temperatures below 10

μ

K, similar to those achieved in conventional MOTs that use collimated laser beams. In addition, we observe trapping of

2\times10^7

Cs atoms in a non-conventional MOT geometry, where the cooling laser beams are diagonal to the principal axis of the quadrupole magnetic field.