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arXiv:1003.1432 · Chinese Physics Letters

Measurement of Spatial Distribution of Cold Atoms in an Integrating Sphere

Xucheng Wang, Hua-Dong Cheng, Ling Xiao, Ben-Chang Zheng, Yan-Ling Meng, Liang Liu, Yuzhu Wang

Published Feb 1, 2012• 13 citations

Abstract

We present an experiment on the measurement of the spatial distribution of cold atoms in a ceramic cell. The atoms are first cooled by diffusing light produced by multiple scattering of laser light at the inner surface of the cell. An in homogeneous magnetic field is applied after the atoms are cooled by using a pair of anti-Helmholtz coils, and thus the shift of atomic magnetic sub-levels is position-dependent. We move the anti-Helmholtz coils point by point while keeping the probe laser beam resonant with the cold atoms at zero magnetic field. The number of cold atoms at different positions can be extracted by detecting the absorption to the probe beam. The density of the cold atoms in the cell is measured in two dimensions perpendicular and parallel to the tube connecting to the vacuum system, respectively. The results show that at the center of the cell, fewer atoms exist due to the leakage of diffuse light into the hole connecting to the vacuum pump. The method we developed is used to detect cold atoms in a region where imaging is impossible.

DOI: 10.1088/0256-307x/29/2/023701

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We present an experiment on the measurement of the spatial distribution of cold atoms in a ceramic cell. The atoms are first cooled by diffusing light produced by multiple scattering of laser light at the inner surface of the cell. An in homogeneous magnetic field is applied after the atoms are cooled by using a pair of anti-Helmholtz coils, and thus the shift of atomic magnetic sub-levels is position-dependent. We move the anti-Helmholtz coils point by point while keeping the probe laser beam resonant with the cold atoms at zero magnetic field. The number of cold atoms at different positions can be extracted by detecting the absorption to the probe beam. The density of the cold atoms in the cell is measured in two dimensions perpendicular and parallel to the tube connecting to the vacuum system, respectively. The results show that at the center of the cell, fewer atoms exist due to the leakage of diffuse light into the hole connecting to the vacuum pump. The method we developed is used to detect cold atoms in a region where imaging is impossible.

In this paper we describe an experiment on laser cooling of

^{87}\mathrm{Rb}

atoms directly from a vapor background in diffuse light. Diffuse light is produced in a ceramic integrating sphere by multiple scattering of two laser beams injected through multimode fibers. A probe beam, whose propagation direction is either horizontal or vertical, is used to detect cold atoms. We measured the absorption spectra of the cold atoms by scanning the frequency of the probe beam, and observed both the absorption signal and the time of flight signal after we switched off the cooling light, from which we estimated the temperature and the number of cold atoms. This method is clearly attractive for building a compact cold atom clock.

Absorption spectra of cold rubidium atoms in an integrating sphere under the influence of a diffuse laser field have been systematically investigated. A pronounced dispersionlike structure centered at the light-shifted pump frequency is observed with a subnatural linewidth. In particular, two clearly resolved absorption resonances on the $5{S}_{1/2}(F=2)\ensuremath{\rightarrow}5{P}_{3/2}({F}^{\ensuremath{'}}=3)$ transitions occur with variable probe beam intensity, which is consistent with our proposed theoretical model. Based on the two absorption resonances,we measure the dependence of light shifts, from which we can directly extract the effective Rabi frequency in a diffuse laser field, on the probe laser intensity, pump laser intensity, and pump laser detuning. Our work helps to identify the physical mechanisms behind these spectral features and is beneficial for studying the corresponding effect in a cold sample.

Two methods of absorption imaging to detect cold atoms in a magnetic trap are implemented for a high-precision cold atom interferometer. In the first method, a probe laser which is in resonance with a cycle transition frequency is used to evaluate the quantity and distribution of the atom sample. In the second method, the probe laser is tuned to an open transition frequency, which stimulates a few and constant number of photons per atom. This method has a shorter interaction time and results in absorption images which are not affected by the magnetic field and the light field. We make a comparison of performance between these two imaging methods in the sense of parameters such as pulse duration, light intensity, and magnetic field strength. The experimental results show that the second method is more reliable when detecting the quantity and density profiles of the atoms. These results fit well to the theoretical analysis.

In this paper we report an experiment on the observation of the recoil-induced resonances (RIR) and electromagnetically induced absorption (EIA) of cold

^{87}\text{R}\text{b}

atoms in diffuse light. The pump light of the RIR and the EIA comes from the diffuse light in an integrating sphere, which also serves the cooling light. We measured the RIR and the EIA signal varying with the detuning of the diffuse laser light, and also measured the number and the temperature of the cold atoms at the different detunings. The mechanism of RIR and EIA in the configuration with diffuse-light pumping and laser probing are discussed, and the difference between the nonlinear spectra of cold atoms in a diffuse-light cooling system and in a magneto-optical trap is studied.