Using the principle of causality as expressed in the Kramers-Kronig relations, we derive a generalized criterion for a negative refractive index that admits imperfect transparency at an observation frequency omega. It also allows us to relate the global properties of the loss (i.e., its frequency response) to its local behavior at omega. However, causality-based criteria rely on the group veloc...

The application of generalized Kramers-Kronig relations, the so-called Leontovich relations, to thermal field theory is discussed. Medium effects contained in the full, thermal propagators can easily be taken into account by this method. As examples the collisional energy loss of a charged particle in a relativistic plasma and the radiation of energetic photons from a quark-gluon plasma are con...

This paper examines the highand low-frequency asymptotic consequences of the Kramers-Kronig relations which hold for the real and imaginary parts of the Fourier transform of the response of any linear causal system. By knowing or assuming the highor low-frequency expansion of one of these functions, the corresponding asymptotic expansion of the other is easily determined, and furthermore the co...

A non-iterative and non-interferometric computational imaging method to reconstruct a complex wave field called synthetic aperture based on Kramers–Kronig relations (KKSAI) is reported. By collecting images through modified microscope system with pupil modulation capability, we show that the phase amplitude profile of sample at limited resolution can be extracted from as few two intensity by us...

The Huttner−Barnett model is extended to a magnetodielectric medium by adding a new matter field to this model. The eigenoperators for the coupled system are calculated and electromagnetic field is written in terms of these operators. The electric and magnetic susceptibility of the medium are explicitly derived and shown to satisfy the Kramers−Kronig relations. It is shown that the results obta...