52,529 research outputs found
Control of lasing in fully chaotic open microcavities by tailoring the shape factor
We demonstrate experimentally that lasing in a semiconductor microstadium can
be optimized by controlling its shape. Under spatially uniform optical pumping,
the first lasing mode in a GaAs microstadium with large major-to-minor-axis
ratio usually corresponds to a high-quality scar mode consisting of several
unstable periodic orbits. Interference of waves propagating along the
constituent orbits may minimize light leakage at particular major-to-minor-axis
ratio. By making stadium of the optimum shape, we are able to maximize the mode
quality factor and align the mode frequency to the peak of the gain spectrum,
thus minimizing the lasing threshold. This work opens the door to control
chaotic microcavity lasers by tailoring the shape factor
Double-layer Perfect Metamaterial Absorber and Its Application for RCS Reduction of Antenna
To reduce the radar cross section (RCS) of a circularly polarized (CP) tilted beam antenna, a double-layer perfect metamaterial absorber (DLPMA) in the microwave frequency is proposed. The DLPMA exhibits a wider band by reducing the distance between the three absorption peaks. Absorbing characteristics are analyzed and the experimental results demonstrate that the proposed absorber works well from 5.95 GHz to 6.86 GHz (relative bandwidth 14.1%) with the thickness of 0.5 mm. Then, the main part of perfect electric conductor ground plane of the CP tilted beam antenna is covered by the DLPMA. Simu¬lated and experimental results reveal that the novel antenna performs well from 5.5 GHz to 7 GHz, and its monostatic RCS is reduced significantly from 5.8 GHz to 7 GHz. The agreement between measured and simulated data validates the present design
Shape-dependence of transmission, reflection and absorption eigenvalue densities in disordered waveguides with dissipation
The universal bimodal distribution of transmission eigenvalues in lossless
diffusive systems un- derpins such celebrated phenomena as universal
conductance fluctuations, quantum shot noise in condensed matter physics and
enhanced transmission in optics and acoustics. Here, we show that in the
presence of absorption, density of the transmission eigenvalues depends on the
confinement geometry of scattering media. Furthermore, in an asymmetric
waveguide, densities of the reflection and absorption eigenvalues also depend
of the side from which the waves are incident. With increas- ing absorpotion,
the density of absorption eigenvalues transforms from single-peak to
double-peak function. Our findings open a new avenue for coherent control of
wave transmission, reflection and absorption in random media.Comment: 9 pages 8 figure
Control of coherent backscattering by breaking optical reciprocity
Reciprocity is a universal principle that has a profound impact on many areas
of physics. A fundamental phenomenon in condensed-matter physics, optical
physics and acoustics, arising from reciprocity, is the constructive
interference of quantum or classical waves which propagate along time-reversed
paths in disordered media, leading to, for example, weak localization and
metal-insulator transition. Previous studies have shown that such coherent
effects are suppressed when reciprocity is broken. Here we show that by
breaking reciprocity in a controlled manner, we can tune, rather than simply
suppress, these phenomena. In particular, we manipulate coherent backscattering
of light, also known as weak localization. By utilizing a non-reciprocal
magneto-optical effect, we control the interference between time-reversed paths
inside a multimode fiber with strong mode mixing, and realize a continuous
transition from the well-known peak to a dip in the backscattered intensity.
Our results may open new possibilities for coherent control of classical and
quantum waves in complex systemsComment: Comments are welcom
Single Top Quark Production and Decay at Next-to-leading Order in Hadron Collision
We present a calculation of the next-to-leading order QCD corrections, with
one-scale phase space slicing method, to single top quark production and decay
process at hadron colliders.
Using the helicity amplitude method, the angular correlation of the final state
partons and the spin correlation of the top quark are preserved. The effect of
the top quark width is also examined.Comment: 47 pages, 9 figure
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