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Superluminal light propagation is typically accompanied by significant absorption that might prevent its observation in realistic samples. We propose an all-optical implementation exploiting the two-photon resonance in three-level media to overcome this problem. With several computational methods, we analyze three possible configurations of optically-dressed systems and identify an optimal configuration for superluminal propagation. Due to the far-detuned operating regime with low absorption, this scenario avoids the usual need for population inversion, gain assistance or nonlinear optical response. Our analysis covers a broad parameter space and aims for the identification of conditions where significant pulse advancement can be achieved at high transmission levels. In this context, a figure of merit is introduced accounting for a trade-off between the desired group-index values and transmission level. This quantity helps to identify the optimal characteristics of the dressing beam.
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http://dx.doi.org/10.1038/s41598-024-62220-x | DOI Listing |
We analyze the dwell time and group delays of electromagnetic waves during transmission and tunneling through complex media, which are non-Hermitian and dispersive. We show that the dwell time, group delays of reflection and transmission, and Dicke times are no longer equal, even though the structure remains mirror symmetric. An additional contribution from the dissipative response of the complex media - termed the energy loss time - must be taken into account.
View Article and Find Full Text PDFWe proposed and demonstrated fast light and superluminal propagation based on Rayleigh scattering-induced Brillouin random lasing resonance in optical fibers. A theoretical model of the proposed Brillouin superluminal propagation system has been established, detailing the principle of optical group velocity manipulation based on the combination of stimulated Brillouin scattering and Brillouin cross-gain modulation, for the first time to the best of our knowledge. Thanks to the randomly distributed Rayleigh scattering, Brillouin random lasing resonance with a single-longitudinal-mode lasing operation essentially contributes to fast light and superluminal propagation of the pump light signals propagating along a kilometer-long optical fiber.
View Article and Find Full Text PDFNat Commun
June 2025
Blackett Laboratory, Department of Physics, Imperial College London, London, SW7 2AZ, UK.
The interaction of light with objects and media moving at relativistic and superluminal speeds enables unconventional phenomena such as Fresnel drag, Hawking radiation, and light amplification. Synthetic motion, facilitated by modulated internal degrees of freedom, enables the study of relativistic phenomena unrestricted by the speed of light. In this study, we investigate synthetically moving apertures created by high-contrast reflectivity modulations, which are generated by ultrafast laser pulses on a subwavelength thin film of indium tin oxide.
View Article and Find Full Text PDFNat Commun
February 2025
Department of Electrical and Computer Engineering, Univ. of Southern California, Los Angeles, CA, USA.
Space-time wave packets (STWPs) with correlated spatial and frequency degrees of freedom exhibit time-dependent spatial interference, thereby giving rise to interesting dynamic evolution behaviors. While versatile spatiotemporal phenomena have been demonstrated in freely propagating fields, coupling spatiotemporal light into multimode fibers remains a fundamental experimental challenge. Whereas synthesizing freely propagating STWPs typically relies on a continuum of plane-wave modes, their multimode-fiber counterparts must be constructed from the discrete set of fiber modes whose propagation constants depend on fiber structures.
View Article and Find Full Text PDFPhys Rev Lett
January 2025
Institut Polytechnique de Paris, Ecole Polytechnique, ENSTA Paris, Laboratoire d'Optique Appliquée, CNRS, 91762 Palaiseau, France.
We demonstrate that pulsed THz radiation produced in air by a focused ultrashort laser pulse can be steered to large angles or even in the backward direction with respect to the laser propagation axis. The emission angle is adjusted by the flying focus technique, which determines the speed and direction of the ionization front created by the single-color laser pulse. This easily adjustable THz source, being well separated from the intense laser, opens exciting applications for remote THz spectroscopy.
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