arXiv subjects

Wei Hu

Publications and source records attributed to Wei Hu.

400 records · Page 23Linked to original sources

arXiv2006

Superluminal group velocity in an anisotropic metamaterial

Based on boundary condition and dispersion relation, the superluminal group velocity in an anisotropic metamaterial (AMM) is investigated. The superluminal propagation is induced by the hyperbolic dispersion relation associated with the AMM. It is shown that a modulated Gaussian beam exhibits a superluminal group velocity which depends on the choice of incident angles and optical axis angles. The superluminal propagation does not violate the theory of special relativity because the group velocity is the velocity of the peak of the localized wave packet which does not carry information. It is proposed that a triglycine sulfate (TGS) crystal can be designed and the superluminal group velocity can be measured experimentally.

physics.optics↗

arXiv2006

Focusing and phase compensation of paraxial beams by a left-handed material slab

On the basis of angular spectrum representation, a formalism describing paraxial beams propagating through an isotropic left-handed material (LHM) slab is presented. The treatment allows us to introduce the ideas of beam focusing and phase compensation by LHM slab. Because of the negative refractive index of LHM slab, the inverse Gouy phase shift and the negative Rayleigh length of paraxial Gaussian beam are proposed. It is shown that the phase difference caused by the Gouy phase shift in right-handed material (RHM) can be compensated by that caused by the inverse Gouy phase shift in LHM. If certain matching conditions are satisfied, the intensity and phase distributions at object plane can be completely reconstructed at the image plane.

physics.optics↗

arXiv2006

Nonlocality-controlled interaction of spatial solitons in nematic liquid crystals

We demonstrate experimentally that the interactions between a pair of nonlocal spatial optical solitons in a nematic liquid crystal (NLC) can be controlled by the degree of nonlocality. For a given beam width, the degree of nonlocality can be modulated by varying the pretilt angle of NLC molecules via the change of the bias. When the pretilt angle is smaller than pi/4, the nonlocality is strong enough to guarantee the independence of the interactions on the phase difference of the solitons. As the pretilt angle increases, the degree of nonlocality decreases. When the degree is below its critical value, the two solitons behavior in the way like their local counterpart: the two in-phase solitons attract and the two out-of-phase solitons repulse.

physics.optics↗

arXiv2005

On the representation dimension of rank 2 group algebras and related algebras

The representation dimension was defined by M. Auslander in 1970 and is, due to spectacular recent progress, one of the most interesting homological invariants in representation theory. The precise value is not known in general, and is very hard to compute even for small examples. For group algebras, it is known in the case of cyclic Sylow subgroups, due to Auslander's fundamental work. For some group algebras (in characteristic 2) of rank at least 3 the precise value of the representation dimension follows from recent work of R.Rouquier. There is a gap for group algebras of rank 2; here the deep geometric methods do not work. In this paper we show that for all n and any field $k$ the commutative algebras k[x,y]/(x^2, y^{2+n}) have representation dimension 3. For the proof, we give an explicit inductive construction of a suitable generator-cogenerator. As a consequence, we obtain that the group algebras in characteristic 2 of the groups C_2 x C_{2^m} have representation dimension 3. Note that for m>2 these group algebras have wild representation type.

math.RT↗