6,816 research outputs found
Synthetic gauge potential and effective magnetic field in a Raman medium undergoing molecular modulation
We theoretically demonstrate non-trivial topological effects for a probe
field in a Raman medium undergoing molecular modulation processes. The medium
is driven by two non-collinear pump beams. We show that the angle between the
pumps is related to an effective gauge potential and an effective magnetic
field for the probe field in the synthetic space consisting of a synthetic
frequency dimension and a spatial dimension. As a result of such effective
magnetic field, the probe field can exhibit topologically-protected one-way
edge state in the synthetic space, as well as Landau levels which manifests as
suppression of both diffraction and sideband generation. Our work identifies a
previously unexplored route towards creating topological photonics effects, and
highlights an important connection between topological photonics and nonlinear
optics
Sideband generation of transient lasing without population inversion
We suggest a method to generate coherent short pulses by generating a
frequency comb using lasing without inversion in the transient regime. We use a
universal method to study the propagation of a pulse in various spectral
regions through an active medium that is strongly driven on a low-frequency
transition on a time scale shorter than the decoherence time. The results show
gain on the sidebands at different modes can be produced even if there is no
initial population inversion prepared. Besides the production of ultra-short
pulse this frequency comb may have applications towards making short-wavelength
or Tera-hertz lasers
Central engine afterglow of Gamma-ray Bursts
Before 2004, nearly all GRB afterglow data could be understood in the context
of the external shocks model. This situation has changed in the past two years,
when it became clear that some afterglow components should be attributed to the
activity of the central engine; i.e., the {\it central engine afterglow}. We
review here the afterglow emission that is directly related to the GRB central
engine. Such an interpretation proposed by Katz, Piran & Sari, peculiar in
pre-{\it Swift} era, has become generally accepted now.Comment: 4 pages including 1 figure. Presented at the conference "Astrophysics
of Compact Objects" (July 1-7, 2007; Huangshan, China
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