Increase of optical resolution by evanescent waves

Frédérique de Fornel

Frédärique de Fornel

Kaifeng Zhao, Z. Wu

The authors describe an atomic magnetometer, the evanescent wave magnetometer, which uses an evanescent wave to measure the Larmor frequency of Rb atoms near the cell surface. The submicron penetration depth of the probe beam allows the evanescent wave magnetometer to achieve a spatial resolution of several tens of microns or better, and greatly reduces the inhomogeneous broadeningdue to magnetic field inhomogeneities. Its noise density in the present experiment is ∼100pT∕Hzfor frequencies between 1 and 10mHz, and decreases to less than 10pT∕Hz as the frequency increases to 25Hz.

V. Savalli, D. Stevens, Jérôme Estève +5 more

We present a high resolution study of the specularity of the atomic reflection from an evanescent wave mirror using velocity selective Raman transitions. We observed a double structure in the velocity distribution after reflection: a peak consistent with specular reflection and a diffuse reflection pedestal whose contribution decreases rapidly with increasing detuning. The diffuse reflection is due to two distinct effects: spontaneous emission in the evanescent wave and roughness in the evanescent wave potential whose amplitude is smaller than the de Broglie wavelength of the reflected atoms.

W. Seifert, Charles S. Adams, V. I. Balykin +3 more

V. Savalli, P. D. Featonby, Vincent Josse +5 more

Summary form only given. Evanescent wave atomic mirrors have been shown to be very sensitive to the surface roughness of the glass substrate on which the evanescent wave is formed. Non-specular reflection of slow atoms at normal incidence has been observed for surface roughness as low as 0.1 nm. We interpret this behaviour in terms of diffraction of the atomic De Broglie wave on the modulated potential created by the interference of the evanescent wave with light scattered by the rough surface. However these experiments could not separate the specular peak of reflected atoms from the diffuse part. We have developed a new method to measure the velocity distribution of the atoms after the bounce with a much better resolution, using Raman transitions. Two phase locked counterpropagating laser beams induce a Raman transition between the ground state hyperfine levels of the /sup 85/Rb atoms falling from a magneto-optical trap. The resonance condition is only fulfilled for atoms with a transverse velocity controlled by the interaction time between the atoms and the beams. These velocity selected atoms bounce on the mirror and their velocity distribution after reflection can be measured using the same Raman beams, by scanning their difference in frequency.