Gravitooptical and near-field traps

Gravitooptical and near-field traps are based on a combined use of electromagnetic and gravitational forces. 

In such a cavity, the transverse (horizontal) size of the atomic mode can be expressed in terms of the distance L from the surface of the mirror to the classical turning point, which determines the length of the cavity. For estimation purposes, the gradient force potential can be taken to be stepped near the surface of the mirror. The shape of the surface of the mirror in the simplest approximation can he treated as a paraboloid of revolution, 

The distance to the upper point of the classical trajectory is determined by the atomic velocity in the neighborhood of the mirror, L = v /2g, and can be associated with the energy of longitudinal motion given by eqn (6.10). With the typical gravitational length being, as indicated above, of the order of a micron, the size of the atom mode is a few tens of microns. 

Note that the intensity of the evanescent wave in an atom mirror can be increased by two or three orders of magnitude on account of excitation of surface plasmons produced by introducing a thin metal layer into the dielectric-vacuum interface (Esslinger et al. 1993). Another method to intensify the evanescent wave is to introduce a dielectric film of high refractive index, which produces a dielectric optical fiber for the laser radiation. The repeated reflection of the laser light from the dielectric-vacuum and dielectric-dielectric interfaces substantially increases the intensity of the evanescent wave (Kaiser et al. 1994). 

Other proposals for near-field traps were examined by Ohtsu (1998), where nearfield effects in the vicinity of nanofiber traps, including combination with van der Waals forces, were discussed. All these proposals are undoubtedly of interest in the rapidly developing area of nanofabrication on the single-atom (or single-molecule) level in the spirit of the ideas put forward by Feynman (1992), which will be discussed in Chapter 7. 

---