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Construction of a Blue Neutral Cesium-133 Magneto-Optical Trap

Madison Whitmore

Published May 1, 2025• 0 citations
OpenAlex

Abstract

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.

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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.
A magneto-optical trap of cesium atoms was generated by applying a circularly polarized cooling laser beam onto a reflective two-dimensional diffraction grating with an aperture and by retroreflecting the incident beam passing through the aperture while reversing the circular polarization. The cooling laser beams comprised the incident, retroreflected, and four diagonally diffracted beams at an angle of 50° with respect to the normal direction of the grating surface. The intensity of the retroreflected beam was carefully adjusted to balance the radiation forces acting on the atoms. A significant number of cold atoms (7.0 × 106) were captured, in spite of the difficulty in a magneto-optical trap of cesium atoms, using nonorthogonal cooling beams owing to the high nuclear spin. The significance of the retroreflected beam in the trapping process was highlighted when the intensity of the retroreflected beam was reduced, resulting in the absence of trapped atoms. Notably, the cold atom cloud was generated near the edge of the region, where all the cooling beams were overlapped. The phenomenon is explained by the numerical calculations of the radiation forces considering all the Zeeman sublevels in the cooling transition and the Gaussian intensity profile of the incident beam.
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.
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 4×1084\times10^84×108 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 μμμK, similar to those achieved in conventional MOTs that use collimated laser beams. In addition, we observe trapping of 2×1072\times10^72×107 Cs atoms in a non-conventional MOT geometry, where the cooling laser beams are diagonal to the principal axis of the quadrupole magnetic field.
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.
Ultracold atoms are a desirable substrate for experiments in quantum optics due to their highly coherent nature. Magneto-Optical Traps (MOTs) are a commonly used apparatus for producing clouds of cold, neutrally charged atoms such as Rubidium. The method relies on the effect of Doppler cooling, where laser light that has been detuned slightly below an atomic resonance results in a net cooling effect on the atoms, and magnetic trapping, where a linear magnetic field gradient results in a position dependent restoring force that traps the desired atoms at a central point. In the UVic AMO lab, we aim to build a MOT that is capable of producing ultracold rubidium clouds with temperatures on the order of 10μK.