相关论文: Faster-than-light effects and negative group delay…
The group velocity for pulses in an optical medium can be negative at frequencies between those of a pair of laser-pumped spectral lines. The gain medium then can amplify the leading edge of a pulse resulting in a time advance of the pulse…
We present a simple electronic circuit which produces negative group delays for base-band pulses. When a band-limited pulse is applied as the input, a forwarded pulse appears at the output. The negative group delays in lumped systems share…
We present a simple electronic circuit which provides negative group delays for band-limited, base-band pulses. It is shown that large time advancement comparable to the pulse width can be achieved with appropriate cascading of…
In this letter we experimentally demonstrate that the signal velocity, defined as the earliest time when a signal is detected above the realistic noise floor, may be altered by a region of anomalous dispersion. We encode information in the…
We consider pulse propagation in a linear anomalously dispersive medium where the group velocity exceeds the speed of light in vacuum (c) or even becomes negative. A signal velocity is defined operationally based on the optical…
Propagation of light pulses through negative group velocity media is known to give rise to a number of paradoxical situations that seem to violate causality. The solution of these paradoxes has triggered the investigation of a number of…
The ability to control the speed and polarisation of light pulses will allow for faster data flow in optical networks of the future. Optical delay and switching have been achieved using slow-light techniques in various media, including…
The propagation of light-pulse with negative group-velocity in a nonlinear medium is studied theoretically. We show that the necessary conditions for these effects to be observable are realized in a three-level $\Lambda$-system interacting…
It says in the report$^1$ by Wang et al. that a negative group velocity $u=-c/310$ is obtained and that a pulse advancement shift 62-ns is measured. The authors claim that the negative group velocity is associated with superluminal light…
We demonstrate the simultaneous propagation of slow- and fast-light optical pulses in a four-wave mixing scheme using warm potassium vapor. We show that when the system is tuned such that the input probe pulses exhibit slow-light group…
We experimentally study the group time delay for a light pulse propagating through hot Rb vapor in the presence of a strong coupling field in a $\Lambda$ configuration. We demonstrate that the ultra-slow pulse propagation is transformed…
Anomalous dispersion cannot occur in a transparent passive medium where electromagnetic radiation is being absorbed at all frequencies, as pointed out by Landau and Lifshitz. Here we show, both theoretically and experimentally, that…
We present new results on the causality violations introduced by the rotating wave approximation commonly used in quantum optics and high-energy physics. We find that the causality violations and faster-than-light signalling induced by the…
The group-velocity of evanescent waves (in undersized waveguides, for instance) was theoretically predicted, and has been experimentally verified, to be Superluminal (v_g > c). By contrast, it is known that the precursor speed in vacuum…
Various experiments have shown superluminal group and signal velocities recently. Experiments were essentials carried out with microwave tunnelling, with frustrated total internal reflection, and with gain-assisted anomalous dispersion.…
Vacuum polarisation in QED in a background gravitational field induces interactions which effectively violate the strong equivalence principle and affect the propagation of light. In the low frequency limit, Drummond and Hathrell have shown…
Photonic tunneling permits superluminal signal transmission. The principle of causality is not violated but the time duration between cause and effect can be shortened compared with an interaction exchange with velocity of light. This…
A comparative analysis of two approaches to description of the light modulation pulse delay in a saturable absorber is presented. According to the simplest model, the delay of the optical pulse is a result of distortion of its shape due to…
When a pulse of light traverses a material, it incurs a time delay referred to as the group delay. Should the group delay experienced by photons be attributed to the time they spend as atomic excitations? However reasonable this connection…
In this paper, we investigate the propagation of the light pulse reflected from the layer system with a graphene layer. We show a tunable transition between positive and negative group delay of the optical pulse reflection in such a layered…