Experimental Zeeman EIT resonances and their Lorentzian fits for the (a) Gaussian and (b) Π laser beam profile
Figure 4. Experimental Zeeman EIT resonances and their Lorentzian fits for the (a) Gaussian and (b) Π laser beam profile. The resonances are obtained under the same conditions like in figure 3(a). Insets show the resonances in the vicinity of their peaks. Residuals, obtained as the difference between the raw data and the corresponding fit, for Gaussian and Π profiles are given in (c) and (d), respectively.
Experimental and theoretical analyses show the effect of laser beam radial intensity distribution on line-shapes and line-widths of the electromagnetically induced transparency (EIT). We used Gaussian and Π (flat top) laser beam profiles, coupling the D1 transition of 87Rb atoms in the vacuum cell in the Hanle experimental configuration. We obtained non-Lorentzian EIT line-shapes for a Gaussian laser beam, while line-shapes for a Π laser beam profile are very well approximated with Lorentzian. EIT line-widths, lower for Gaussian than for Π, show nonlinear dependence on laser intensity for both laser beam profiles. EIT amplitudes have similar values and dependence on laser intensity for both laser beams, showing the maximum at around 0.8 mW cm−2. Differences between the EIT line-shapes for the two profiles are mainly due to distinct physical processes governing atomic evolution in the rim of the laser beam, as suggested from the EIT obtained from the various segments of the laser beam cross-section.