DOI: 10.1051/jp4:2004119072 An atom interferometer using thermal lithium atoms

Abstract. We have built an atom interferometer of the Mach-Zehnder type, operating with thermal lithium atoms [1]. Its design is largely inspired by previous works done by the groups of D. Pritchard [2], A. Zeilinger [3] and S.A. Lee [4]. In our apparatus, the atomic wave is diffracted in the Bragg regime by three laser sanding waves to achieve a Mach-Zehnder configuration. This paper briefly recalls the diffraction process and shows the experimental results obtained in our group. Our apparatus is able to achieve a high fringe contrast of 74 % with a large mean detected atom flux of 1.5 × 104 s-1. Finally, the paper ends with the measurement of the velocity distribution of our lithium beam using a light induced fluorescence technique. 1. DIFFRACTION OF THE LITHIUM ATOMIC WAVE IN THE BRAGG REGIME Diffraction of an atomic wave by a laser standing wave in the Bragg regime is in complete analogy with diffraction of x-rays by a crystal. The laser standing wave acts as a thick phase grating for the atomic wave with a periodicity of half the laser wavelength λ r. The diffraction process is governed by conservation of momentum and energy. With a thick laser wave, momentum is transferred from the laser to the incident atomic wave only when the Bragg condition λr sin(θB) = pλdB is fulfilled, where θB is the Bragg angle and p is the diffraction order. For lithium, λr = 671 nm, and the first order diffraction angle is θ1 = 2θB = 170 µrad. Diffraction of the lithium atomic wave is seen by tuning the angle i between the mirror and the atomic beam axis as shown in figure 1a. Figure 1b presents the zero-order beam intensity measured with our detector. This signal is symmetrical around the beam axis and the Bragg condition is fulfilled for ±1 diffraction orders. Figure 1a. Experimental set-up for Bragg diffraction. Figure 1b. Zero-order beam intensity as a function of the angle i between the mirror and the beam axis