Polarization-rotation resonances with subnatural widths using a control laser

¹ Department of Physics, Indian Institute of Science - Bangalore 560 012, India
² Centre for Quantum Technologies, National University of Singapore - Singapore
³ Department of Physics, Indian Institute of Technology - Roorkee 247 667, India

Received: 13 February 2014
Accepted: 28 April 2014

Abstract

We demonstrate extremely narrow resonances for polarization rotation in an atomic vapor. The resonances are created using a strong control laser on the same transition, which polarizes the atoms due to optical pumping among the magnetic sublevels. As the power in the control laser is increased, successively higher-order nested polarization-rotation resonances are created, with progressively narrower linewidths. We study these resonances in the D₂ line of Rb in a room temperature vapor cell, and demonstrate a width of for the third-order rotation. The physical basis for the observed resonances is that optical pumping results in a simplified ΛV-type level structure with differential dressing of the levels by the control laser, which is why the control power has to be sufficiently high for each resonance to appear. This explanation is borne out by a density-matrix analysis of the system. The dispersive lineshape and subnatural width of the resonance lends itself naturally to applications such as laser locking to atomic transitions and precision measurements.