Abstract

With the advent of laser cooling, the interest in "optical elements," like mirrors, lenses, and beam splitters for atoms, has been increasing rapidly over the last years. For use of such elements in atom interferometers these elements are required to be "coherent," that is, preserve the phase of the atomic wave. Therefore, no spontaneous emission should occur during the interaction with the optical element. This means that the excited state of the atom should not be populated, and therefore large detunings from the atomic resonance should be used. However, at larger detunings a correspondingly large laser intensity is required to achieve sufficiently high potentials. For an atomic mirror, we use the evanescent wave that is formed by total internal reflection of a strong laser beam in a (glass) prism. The evanescent wave provides a strong intensity gradient, and thus combines a large potential with a very short interaction time, thereby limiting spontaneous emission even further. To reflect sodium atoms with a velocity of 1 m/s, at a detuning of 2 GHz, a laser intensity of ≈6 W/cm² is required. To obtain a reasonable reflective area mirror, this means a laser power of≈1 W is required, just barely within the range of commercial dye lasers. We achieve high laser intensities over a bigger spot size by coupling the laser to a thin dielectric wave guide, that is deposited on a prism. Thus we obtain an evanescent wave which is a factor of 100–1000 stronger than would be the case for the bare prism.¹

© 1994 IEEE