Luca Spani Molella

Electromagnetically induced transparency, electromagnetically induced absorption and giant Kerr effect in closed degenerate two level systems

Spontaneous transfer of coherence has proven to be a good interpretative scheme for the explantation of the spectra of a probe laser probing a closed degenerate two-level systems. With its aid it was possible to give an explanation for the emergence of electromagnetically induced absorption and also to make predictions on the associated coupling laser spectra. Here we extend our work on the role of the coupling laser in electromagnetically induced absorption presenting new measurements of the probe and coupling laser absorption and dispersion spectra - taken in the D2 line of caesium - which reassert the importance of spontaneous transfer of coherence in the generation of electromagnetically induced absorption spectra. All measurements were performed with linearly polarised coupling and probe laser of orthogonal polarisation, acting on a perpendicularly propagating caesium atomic beam to minimise the Doppler broadening of the lines. For sake of completeness we compared the electromagnetically induced absorption spectra with electromagnetically induced transparency spectra obtained in another two-level system within the same line. The measured probe spectra were used to calculate the refractive index of caesium in the presence of electromagnetically induced transparency and absorption. On that basis we could calculate the effect of Kerr nonlinearities and measure nonlinear Kerr coefficients of the order of n2 ≈ 10-5 cm2/mW with absorption coefficients of the order of &agr; ≈ 0.1 cm-1.

Experimental Comparison between the Index of Refraction in Strongly Driven and Degenerate Two-Level Systems

Negative dispersion and transparency in a strongly driven calcium two-level system and positive dispersion and transparency or anomalous dispersion and enhanced absorption in closed degenerate two-level systems in caesium have been observed using pump-probe spectroscopy.

Inversion of the Coupling Absorption at the Two-Photon Resonance in a Coupling-Probe-Spectroscopy Experiment

After the discovery of electromagnetically induced absorption (EIA), both theoretical and experimental research was performed to explain not only the probe laser absorption and dispersion spectra, but also those of the coupling laser. The investigations of EIA in degenerate two-level systems have often been realized using two linearly polarized lasers of orthogonal polarization [1]. However, the simplest configuration leading to EIA is the so-called N-system [2] which basically requires the simultaneous adoption of a circularly polarized coupling laser and a linearly polarized probe (here called σ−π). To our knowledge, no experimental measurements of the coupling laser exist in the configurations (σ+−σ−, π−σ− or σ+−π).

Giant Kerr effect in degenerate closed transitions

Giant Kerr nonlinearities about twelve orders of magnitudes greater than in glass were measured under negligible absorption conditions within two different closed transitions of the cesium D2 line characterized y electromagnetically induced transparency or absorption.

Coherent population trapping in a closed transition

This paper provides insight into the behaviour of the coupling laser which occur in a typical electromagnetically induced absorption closed transition. In this research different closed transitions of the /sup 133/Cs D/sub 2/ line are analysed with a probe and a coupling laser. A phenomenological computational model of the dispersion pattern is also developed, which gives good agreement with the taken measurements. A full theoretical analysis of the details for the system is presently under development.