Laser-cooling methods

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. 

Future Trends. Methods of laser cooling and trapping are emerging as of the mid-1990s that have potential new analytical uses. Many of the analytical laser spectroscopies discussed herein were first employed for precise physical measurements in basic research. AppHcations to analytical chemistry occurred as secondary developments from 10 to 15 years later. 

A variation of the method utilizes a laser as the heat source.52,53 This nonequilibrium technique involves fast growth and rapid heating/cooling rates (100 000 K s-1) in the reaction zone. Ochoa et al. (chapter 27), provide a synopsis of the laser pyrolysis method and describe an Fe3C product used for catalysis. 

With only one exception, every experiment on BEC has employed laser cooling and trapping methods to create a gas of cold atoms. The exception is hydrogen. The recoil energy of hydrogen is so large that the gas cannot be cooled below a few millikelvin, with densities far from the transition. (The Amsterdam group... 

Both microwave and optical frequency standards have benefited greatly from the development of the laser and the methods of laser spectroscopy in atomic physics. In particular, the ability to determine both the internal and external (that is, motion) atomic states with laser light - by laser cooling for example - has opened up the prospect of frequency standards with relative uncertainties below lO, for example, the Cs atomic fountain clock. The best atomic theories in some cases at starting to match in accuracy that of measurement, providing thereby refined values of the fundamental, so-called atomic constants. Even quite practical measurements (such as used in GPS navigation and primary standards of length) have advanced in recent years. 

In the amplitude method, the motion of the ions over many oscillation periods (typically 10 periods) is integrated such that it is the modulation frequency-dependent amplitude that is observed. The most precise determinations of the normal mode frequencies are found through fitting the relevant expression for z (co) (that is Equation 10.14 for identical ions and Equation 10.16 for non-identical ions) to the measured amplitudes of the laser-cooled ion as a function of the drive frequency, as shown in... 

Molecular ions can be produced, trapped and cooled by the application of a variety of techniques. Within this laboratory, we can use essentially three methods (1) reaction of trapped and laser-cooled atomic ion species with neutral molecules in a gas leaked into the vacuum chamber of the ion-trap apparatus (11) electron impact ionization, using an electron gun, of neutral molecules leaked into the ion-trap center (see Figure 10.3) and (III) photoionization of leaked-in neutral molecules. 

An alternative method for overcoming the Doppler tuning problem in laser cooling has been demonstrated by Ertmer et al. 52] Instead of using a spatially varying magnetic field these authors controlled the frequency of the laser by means of an electro-optic modulator, driven by a radiofrequency source. Varying the frequency of the r.f. field applied produces sidebands to the laser frequency and these can be swept in step with the Doppler shift. 

H. Metcalf, Laser cooling and magnetic trapping of neutral atoms, in Methods of Laser Spectroscopy, ed. by Y. Prior, A. Ben-Reuven, M. Rosenbluth (Plenum, New York, 1986),... 

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