Contrast Measurements of CPT resonances Formed on the 87Rb D1 and D2 Line

Full text: We present investigations on contrast measurements of Coherent Population Trapping (CPT) resonances used to improve the noise performance of a new compact Coupled Dark State Magnetometer (CDSM). CPT can be understood as a quantum interference effect, which occurs in an atomic three level excitation system in the simplest case. The CPT resonances - representing so called dark states - can obtain line widths of about 30 Hz (about seven orders of magnitude smaller than the width of the optical transition), therefore this phenomenon can be used for precision measurements. In our experiment several three level excitation systems are established via a modulated vertical-cavity surface-emitting laser within the hyperfine structure of the 87Rb D1 and D2 lines. In our setup the contrast of the CPT resonances for the excitation of the D1 and D2 line is determined by an indirect contrast measurement method well-suited for small CPT resonance amplitudes with low signal-to-noise ratio. We report an increase of the contrast for the excitation of the D1 line compared to the D2 line. This is mainly caused by a different number of hyperfine levels contributing to the excitation process. In our case the excited state 52P1/2 of the D1 line has half of hyperfine levels compared to the excited state 52P3/2 of the D2 line. In the latter case not all excited state levels contribute to the preparation of the CPT resonances. Those levels, being not involved in the CPT resonance creation, will lead to a decreased excitation efficiency of the atomic level population into the dark states. As a consequence, in the case of the D2 line excitation the contrast of the CPT resonances is reduced significantly. For this reason the D1 line excitation is preferable in applications like compact CPT atomic clocks and magnetometers. (author)