Heterodyne measurements of dispersion in electromagnetically induced absorption
Liang-Hong Mo, K. Danzmann
Abstract
The dispersive and absorptive features of a closed transition in atomic cesium are investigated by means of a heterodyne interferometer as a function of the powers of probe and pump laser. Coherent population trapping (CPT) phenomena have raised the interest of the community in recent years. Possible applications of such effects are in the field of slow light propagation and, on the other side, superluminal effects. In particular, special interest has been devoted to the investigation of the refractive index of coherently prepared atoms. The goal of this investigation is the design of new optical media which show either negative or positive dispersion without absorption or with increased anomalous absorption. Such media could be useful ui building white light cavities, opto-optical modulators, and in quantum non-demolition (QND) measurements which are crucial to the development of the future generations gravitational wave detectors. Among these coherency processes we have been studying the phenomenon of electromagnetically induced absorption (EIA) (2) in a closed transition in cesiumatoms. The transition under analysis was the 'CS DZ line at 852 nm, in particular the hyperfine transition 6s zS~/2 F=4 + 6p 2P~/2 F'=5. The system was analyzed by means of a three beam heterodyne interferometer (l). This experimental setup shows high sensitivity to phase measurements and strongly reduced sensitivity to acoustical or vibrational noise. Using a third reference laser which does not interact with the mediumone can perform simultaneous measurements of the phase shift and the absorption of either the probe or the pump laser. The dispersion and the absorption of probe and coupling lasers have been measured as a funcion of the power of the coupling and probe lasers themselves. The power of the lasers are changed in the range of several decades. The halfwidth of the EL4 signal shows an increase with respect to the power of the probe laser while the phase shift of the probe laser decreases. The possibility to extend EIA measurements to a closed four level system in cesium is under analysis and is discussed here. Such possible developments of the experimental setup using a fourth laser or modulating the present reference laser enhance the capability to exploit simultaneous measurements of dispersion and absorption even in the four level system. This work was supported by SFB 407 of the Deutsche Forschungsgemeinschaft (German Research Society).