|MadSci Network: Physics|
In the laser cooling process, high velocity atoms (thus also having a large Doppler shift) absorb photons from a laser, tuned near their resonance frequency and directed toward the atomic beam. Each time an atom absorbs a photon from the laser beam, its momentum decreases by the amount of momentum carried by the photon and the atom will slow down in that linear direction. The absorbed photon is then reemitted in a random direction which results in heating. Additionally, thermal background atoms limit the lifetime of the optical trap and ultimately heat the sample as well. Specifically, the cooling efficiency, suffers as the optical trap becomes heated and the its lifetime becomes limited. Recall that the whole idea of laser cooling is that linear kinetic energy of the atoms is reduced. Thus, the heat generated within the optical trap is easy transferred to the atoms contained within, thereby increasing their motion. The inefficiency in this process comes from the design, shape, and coatings used to construct the optical trap. However, what is changed by fixing these problems (in addition to using larger power lasers), which many have done, is to increase the trapping/collection efficiency (the number of atoms trapped verses the number produced). Theses efficiencies range from 0.3% to over 50%. References: S. Bali, et al., Phys. Rev. A 60, R29-32 (1999) M. Stevens, et al., Phys. Rev. Lett. 72, 3787-3790 (1994) T. Dinneen, et al., Rev. Sci. Inst. 67, 752-755 (1996) R. Guckert, et al., Nucl. Instrum. Methods Phys. Res. B 126, 383-385 (1997)
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