Cooling Raman

The recoil limit can be overcome by a recently discovered cooling scheme called Raman cooling (Fig. 9.29). Here a stimulated Raman scattering process is used, which traverses from level 1 via a virtual level down to level 3. If the levels 1 and 3... 

The numerical examples illustrates that the usual techniques of optical cooling are not sufficient to reach BEC at realistic atomic densities unless one uses the experimentally difficult Raman-cooling or the coherent generation of dark states (see Sect. 7.10). 

The Chu experiment produced quasibound molecules from Raman-cooled Cs atoms, but other experiments have been able to form cold molecules directly from atomic Bose-Einstein condensates. The Ketterle group at MIT accomplished Na2 formation from a Na BEC with an... 

Raman cooling uses a two-photon transition between two h q)erfine-structure levels in the ground state of the atom and provides coherent displacement of parts of the velocity distribution toward zero velocity. Such cooling was successfully demonstrated in an experiment by Kasevich and Chu (1992). Consider a three-level A-atom in which 1) and 2) are the lower energy levels and e) is the upper level, placed in the field... 

Fig. 5. 14 (a) Energy-level diagram for Raman cooling based on a two-photon transition between two hyperfine-structure components of the ground atomic state, (b) Atomic velocity distribution before (1) and after (2) Raman cooling. The insert shows the central velocity peak and the velocity width relative to the recoil velocity. (Reprinted from Kasevich and Chu 1992 with courtesy and permission of the American Physical Society.)... 

Chang T-C and DIott D D 1988 Picosecond vibrational cooling in mixed molecular crystals studied with a new coherent Raman scattering technique Chem. Phys. Lett. 147 18-24... 

D. Frequencies Molecules vibrate (stretch, bend, twist) even if they are cooled to 0 K. This is the basis of infrared/Raman spectroscopy, where absorption of energy occurs when the frequency of molecular... 

Kozlov D. N., Pykhov R. L., Smirnov V. V., Vereschagin K. A., Burshtein A. I., Storozhev A. V. Rotational relaxation of nitrogen in argon collisional broadening of Q-branch components in coherent Raman spectra of cooled gas, J. Raman Spectr. 22, 403-7 (1991). 

Keywords atom interferometry, laser cooling, Raman transition... 

Ionic polysulfides dissolve in DMF, DMSO, and HMPA to give air-sensitive colored solutions. Chivers and Drummond [88] were the first to identify the blue 83 radical anion as the species responsible for the characteristic absorption at 620 nm of solutions of alkali polysulfides in HMPA and similar systems while numerous previous authors had proposed other anions or even neutral sulfur molecules (for a survey of these publications, see [88]). The blue radical anion is evidently formed by reactions according to Eqs. (5)-(8) since the composition of the dissolved sodium polysulfide could be varied between Na2S3 and NaaS with little impact on the visible absorption spectrum. On cooling the color of these solutions changes via green to yellow due to dimerization of the radicals which have been detected by magnetic measurements, ESR, UV-Vis, infrared and resonance Raman spectra [84, 86, 88, 89] see later. 

Anti-Stokes picosecond TR spectra were also obtained with pump-probe time delays over the 0 to 10 ps range and selected spectra are shown in Figure 3.33. The anti-Stokes Raman spectrum at Ops indicates that hot, unrelaxed, species are produced. The approximately 1521 cm ethylenic stretch Raman band vibrational frequency also suggests that most of the Ops anti-Stokes TR spectrum is mostly due to the J intermediate. The 1521 cm Raman band s intensity and its bandwidth decrease with a decay time of about 2.5 ps, and this can be attributed the vibrational cooling and conformational relaxation of the chromophore as the J intermediate relaxes to produce the K intermediate.This very fast relaxation of the initially hot J intermediate is believed to be due to strong coupling between the chromophore the protein bath that can enable better energy transfer compared to typical solute-solvent interactions. ... 

Figure 7. Raman spectra of silica gel heated to 600°C, cooled to room temperature and exposed to water vapor (100% RH) for the indicated times. (Reproduced with permission from Ref. 47. Copyright 1986 Materials Research Society.)...

In addition to quantitative crystallinity data, IR and Raman have been proven valuable tools to extract information on chain conformation in the three major phases [112-114], local order in amorphous polymers [115,116] high throughput characterization [117] and structural and polymorphic changes on heating and cooling semi-crystalline polymers [118-120]. 

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