Topic
Group velocity
About: Group velocity is a research topic. Over the lifetime, 10051 publications have been published within this topic receiving 204007 citations. The topic is also known as: group speed.
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TL;DR: In this article, the linear response of a gas in the state with Bose-Einstein condensate to the perturbation by an external electromagnetic field (weak laser pulse) is studied theoretically.
Abstract: We study theoretically the linear response of a gas in the state with Bose-Einstein condensate to the perturbation by an external electromagnetic field (weak laser pulse). The Green’s functions formalism is used to study the dispersion characteristics of a system at finite temperatures. It is shown that the group velocity of the near-resonant pulses in condensate in some cases can strongly depend on the temperature. Basing on the account of the Zeeman splitting of the magnetic states we study also a possibility to filter light pulses by the condensate with several occupied quantum states.
TL;DR: In this article , measurements of Kerr nonlinearity and group velocity dispersion in In0.53Ga0.47As/InP and GaAs0.51Sb0.49/INP ridge waveguides in the mid-infrared using four-wave mixing at ≈ 5 µm.
Abstract: We report measurements of Kerr nonlinearity and group velocity dispersion in In0.53Ga0.47As/InP and GaAs0.51Sb0.49/InP ridge waveguides in the mid-infrared using four-wave mixing at λ ≈ 5 µm. Measured values of Kerr nonlinearity are significantly higher compared to those reported for any other materials systems suitable for building dielectric waveguides with low losses and low group velocity dispersion in the mid-infrared (λ ≈ 3–15 μm). Our measurements establish both In0.53Ga0.47As/InP and GaAs0.51Sb0.49/InP materials as promising platforms for the development of on-chip mid-infrared frequency comb generation and supercontinuum light sources.
TL;DR: In this article , the dot product of a scaled displacement vector with both sides of the elastic wave equation and rearranging terms was used to identify two relevant computational formulas for the group-velocity and slowness vectors.
Abstract: Determination of the phase-velocity direction in anisotropic media is important in the general research of wave phenomena and in the construction of seismic modeling, imaging, and inversion algorithms for practical applications. By taking the dot-product of a scaled displacement vector with both sides of the elastic wave equation and rearranging terms, we identify two relevant computational formulas for the group-velocity and slowness vectors. The quantity in the numerator of this group-velocity vector is linked to the conventional Poynting vector which points in the group-velocity direction, and we thus refer to it as the direction vector for the group-velocity direction. Similarly, the quantity in the numerator of this slowness vector provides a new direction vector which points in the phase-velocity direction, and we thus refer to it as the direction vector for the phase-velocity direction. This new direction vector provides a convenient way to directly compute the phase-velocity direction by using extrapolated vector wavefields in general anisotropic media. We vali- date the effectiveness of the proposed Poynting vector for the phase-velocity direction by using an analytical relation in a homogeneous transversely isotropic medium. After that, three anisotropic models are used to show the differences between the group-velocity and phase-velocity directions, which are estimated by using the direction vectors for the group- velocity and phase-velocity directions. The proposed direction vector is also suitable for the computation of the phase-velocity direction in low-symmetry anisotropic media, including orthorhombic, monoclinic, or triclinic media.
TL;DR: In this paper , phase and group velocities of the A0 guided wave mode, propagating in a unidirectional carbon fiber reinforced laminate, were investigated experimentally and through finite element analysis.
TL;DR: In this paper , a counter-propagation waves coupling mechanism is proposed which is expected to realize an electromagnetically induced transparency (EIT)-like effect, where the transparency window breadths of transmission spectra are greatly enhanced and the corresponding phase shift spectra possess a flat profile or a square profile.
Abstract: In this paper, a new counter-propagation waves coupling mechanism is proposed which is expected to realize an electromagnetically induced transparency (EIT)-like effect. Comparing the travelling waves coupling mechanism (see J. Mod. Opt. 2015,62:313-320 [9]) with the counter-propagating waves coupling mechanism, we find out that the transparency window breadths of transmission spectra are greatly enhanced and the corresponding phase shift spectra possess a flat profile or a square profile. Our numerical simulated results are in good agreement with the theoretical analysis. The EIT-like effect can significantly reduce the group velocity near the edge of the square profile transparent window. We believe that the counter-propagating waves coupling mechanism is particularly beneficial for the realization of active manipulation of slow light devices (such as delay lines) required in the conventional EIT scheme. In the vicinity of the transparency peak, we can obtain a large group delay, may gain more significant potential applications in slow-light transmission and optical storage.