Polarization memory length

As a result, the atomic state populations as well as the polarization in the atomic flux departing from the surface are different from those in the flux arriving at it. This distinction carries information on the relaxation processes in the close vicinity of the surface. It is reasonable to introduce "memory lengths" which determine the characteristic distances at which this information is still contained in the departing flux. Then the population memory length can be defined as l = VjT, whereas the polarization memory length h = VjTi (Bordo and Rubahn 2004). 

Excitation of the gas by an evanescent wave introduces a pure imaginary z-component of the wave vector kf and, hence, an additional time-of-flight broadening of the fluorescence lines. The fluorescence line intensity is determined by the gas volume where the polarization corresponding to the contributions given by either Eq. (7.40) or Eq. (7.41) is essentially nonzero. Therefore, the intensity of emission at the frequency w is proportional to the EW penetration depth, 5, whereas that at the frequency mo is proportional to the polarization memory length, lx = ut/t (see Section 2.4.3). The latter line is thus dominant in the spectrum if <5 [Pg.189]

Problem 7.4. The vapor spectra excited by an evanescent wave will depend strongly on the change of the vapor polarization in vapor-surface scattering if the evanescent wave penetration depth is less than or comparable with the polarization memory length, i.e.,... 

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