Optical molasses

Figure Cl.4.5. Population modulation as the atom moves through the standing wave in the Tin-periD-lin one dimensional optical molasses. The population lags the light shift such that kinetic is converted to potential energy then dissipated into the empty modes of the radiation field by spontaneous emission (after 1171).

The most recent approach to reductive nanofabrication that can indeed constmct nanoscale stmctures and devices uses microscopic tools (local probes) that can build the stmctures atom by atom, or molecule by molecule. Optical methods using laser cooling (optical molasses) are also being developed to manipulate nanoscale stmctures. 

Optical trapping can also be used as a hthographic tool (90). For example, a combination of optical molasses and an optical standing wave have been used to focus a beam of neutral sodium atoms and deposit them in the desired pattern on a suitable substrate (eg, siUcon). Pattern resolutions of the order of 40 nm with good contrast (up to 10 1 between the intended features and the surrounding unpattemed areas) and deposition rates of about 20 nm /min were obtained (90). 

In 1991. a research team tEcole Normal Superieure. Parist reported the cooling of a sample of cesium atoms to 2.5 pK. At about the same lime, a research group (.hunt Institute for Laboratory Astrophysics. Boulder. Coloiado) inputted the achievement ol 5 iK The aforementioned "optical molasses" technique was used in both eases. 

C. Nuclear Dynamics of Expansion of Optical Molasses VI. Epilogue... 

Concurrently, the world of ultracold systems has expanded its boundaries during the last decade to encompass ultracold, three-dimensional, large hnite systems [e.g., ( He)jy clusters (N = 2-10" ), and ( He)jy clusters (N = 25-10 )] in the temperature range of T = 0.1-2.2 K [6-11, 50-78], finite optical molasses in laser irradiated ultracold atomic gases in the temperature range of 10-100 pK [79], as well as finite Bose-Einstein condensates in the temperature range of 10-100 nK [14, 80],... 

Ultracold laser irradiated, finite atomic clouds, referred to as optical molasses—for example, Rb at T = 10 " -lO K [79]. 

Zero-point energy effects can be traced to the light masses of the constituents in quantum clusters and to the extremely low temperatures in the optical molasses and condensates. The zero-point energy effects can be described in terms of the ratio A of the quantum lengths... 

Figure 3. The temperature dependence of the thermal de Broglie wavelengths for several atomic and molecular systems. The relevant temperature domains for Bose-Einstein condensates, optical molasses, and ( He)jy clusters are marked on the hgure.

Figure 23. Dynamics of spatial expansions of optical molasses of Rb adapted from Pmvost et al. (data from Ref. 79). (a) A photograph of the irradiated cloud at r = 0. (b) Excited atom distribution in the irradiated cloud at r = 0. (c) Time dependence of the cloud radius, (d) Time dependence of the volume of the irradiated cloud, (e) Time dependence of the density of the expanding cloud.

Figure 24. The time-dependence temperature of the expanding optical molasses of Rb (data from Ref. 79).

Both the cluster Coulomb explosion time Tex and the expansion time of optical molasses Tm obey the relation [Eq. (114)] Tex, tm oc We... 

We are grateful to Professor Peter Toennies for most stimulating and inspiring discussions and correspondence, and we thank Dr. Laurence Pruvost for fruitful collaboration on the dynamics of optical molasses. This research was supported in part by the German—la aeh James Franck Program on Laser-Matter Interaction. 

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