Conductivity-dependent absorption-free, gain-assisted superluminal propagation and rotary photon drag

Abstract Superluminal light propagation and photon drag are subjects of immense scientific interest owing to potential fundamental and technological implications in the fields of atomic and molecular physics, condensed-matter physics, quantum optics, nanoplasmonics, nanophotonics, and nanoelectronics. In this paper, we present a systematic study on the optical properties, rotary photon drag and superluminal propagation in a conducting gain medium comprising a four-level invert-N-type atomic system. In particular, to explore the nature of light propagation, as to whether subluminal or superluminal, we aim to investigate optical properties of the medium in view of the derived expression of group index, group velocity, group delay, phase delay and photon drag. Interestingly, by tuning the spectral parameters of the proposed system, we predict gain-assisted, absorption-free propagation and superluminality at positive and negative group velocity for positive and negative refractive indices of the medium, respectively. The medium, subjected to various spectral conditions, displays an interesting switching from ON-resonance single absorption peak in the probe field spectrum to an ON-resonance absorption-free region between two OFF-resonance absorption peaks to OFF-resonance gain singlet accompanied by OFF-resonance absorption peak. The maximum calculated values of positive and negative superluminal group velocities of the light pulse are of order 4 × 10 8 m / s both at positive and negative group indices, respectively. On the other hand, the maximum value of photon drag calculated is of order 6.4 × 10 − 7 radian.