MadSci Network: Physics

Re: is this efficiency rating equal to the doppler shift?

Date: Fri Jan 18 11:48:48 2002
Posted By: Robert Arts, Faculty, Physics, Pikeville College
Area of science: Physics
ID: 1010251939.Ph

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%.  


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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