Coherent population trapping resonance on degenerate two-level system for magnetic field measurement

Coherent population trapping (CPT) resonances on the degenerate two-level system of the (F-8=2 --> F-c=1) transition of the Rb-87 D-1 line were investigated in an uncoated vacuum cell by means of level-crossing type experiments - sweeping a magnetic field around zero value and using a single laser beam. The two-photon resonance manifests itself as fluorescence canceling when the system of levels is degenerate (at zero point of magnetic field)(1). The influence of weak transverse magnetic fields on the amplitude and width of the resonance was investigated. The CPT resonances were observed with linear, circular and elliptical polarized laser light. Transverse magnetic field widens the resonances obtained by linear and circular polarization but splits the resonance created by slightly elliptically polarized laser light. The dependence of this splitting on the elliptical ratio and experimental geometry were investigated. Due to its narrow width and sensitivity to low magnetic fields (<1 G) this resonance is very promising for small magnetic field measurement.