Experimental EIT obtained from only a small circular portion (0.5 mm in diameter) of the laser beam transmitted through the Rb cell when this portion is (a) on the beam axis (r = 0.0 mm) and (b) near the beam edge (r = 1.5 mm)

Figure 7. Experimental EIT obtained from only a small circular portion (0.5 mm in diameter) of the laser beam transmitted through the Rb cell when this portion is (a) on the beam axis (r = 0.0 mm) and (b) near the beam edge (r = 1.5 mm).

Abstract

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.