47,659 research outputs found
Cylindrical Superlens by a Coordinate Transformation
Cylinder-shaped perfect lens deduced from the coordinate transformation
method is proposed. The previously reported perfect slab lens is noticed to be
a limiting form of the cylindrical lens when the inner radius approaches
infinity with respect to the lens thickness. Connaturality between a
cylindrical lens and a slab lens is affirmed by comparing their eigenfield
transfer functions. We numerically confirm the subwavelength focusing
capability of such a cylindrical lens with consideration of material
imperfection. Compared to a slab lens, a cylindrical lens has several
advantages, including finiteness in cross-section, and ability in lensing with
magnification or demagnification. Immediate applications of such a cylindrical
lens can be in high-resolution imaging and lithography technologies. In
addition, its invisibility property suggests that it may be valuable for
non-invasive electromagnetic probing.Comment: Minor changes to conform with the published versio
Compact, fiber-compatible, cascaded Raman laser
Cascaded Raman Stokes lasing in an ultrahigh-Q silica microsphere resonator coupled to a tapered fiber is demonstrated and analyzed. With less than 900 μW of pump power near 980 nm, five cascaded Stokes lasing lines are generated. In addition, a threshold power of 56.4 μW for the first-order Stokes lasing is achieved. The Stokes lasing lines exhibit distinct characteristics depending on their order, as predicted by theoretical analysis
Trace forms of Galois extensions in the presence of a fourth root of unity
We study quadratic forms that can occur as trace forms of Galois field
extensions L/K, under the assumption that K contains a primitive 4th root of
unity. M. Epkenhans conjectured that any such form is a scaled Pfister form. We
prove this conjecture and classify the finite groups G which admit a G-Galois
extension L/K with a non-hyperbolic trace form. We also give several
applications of these results.Comment: 19 pages, to appear in International Math Research Notice
Large anisotropy in the optical conductivity of YNi2B2C
The optical properties of YNiBC are studied by using the
first-principles full-potential linearized augmented plane wave (FLAPW) method
within the local density approximation. Anisotropic behavior is obtained in the
optical conductivity, even though the electronic structure shows 3D character.
A large peak in is obtained at 2.4 eV. The anisotropic optical
properties are analyzed in terms of interband transitions between energy levels
and found that the Ni site plays an important role. The electronic energy loss
spectroscopy (EELS) spectra are also calculated to help elucidate the
anisotropic properties in this system.Comment: revtex4, 4 pages, 5 figures, to appear in PR
Ultralow-threshold erbium-implanted toroidal microlaser on silicon
We present an erbium-doped microlaser on silicon operating at a wavelength of 1.5 mum that operates at a launched pump threshold as low as 4.5 muW. The 40 mum diameter toroidal microresonator is made using a combination of erbium ion implantation, photolithography, wet and dry etching, and laser annealing, using a thermally grown SiO2 film on a Si substrate as a starting material. The microlaser, doped with an average Er concentration of 2x10^(19) cm(-3), is pumped at 1480 nm using an evanescently coupled tapered optical fiber. Cavity quality factors as high as 3.9x10^(7) are achieved, corresponding to a modal loss of 0.007 dB/cm, and single-mode lasing is observed
Luminosity Profiles of Merger Remnants
Using published luminosity and molecular gas profiles of the late-stage
mergers NGC 3921, NGC 7252 and Arp 220, we examine the expected luminosity
profiles of the evolved merger remnants, especially in light of the massive CO
complexes that are observed in their nuclei. For NGC 3921 and NGC 7252 we
predict that the resulting luminosity profiles will be characterized by an
r^{1/4} law. In view of previous optical work on these systems, it seems likely
that they will evolve into normal ellipticals as regards their optical
properties. Due to a much higher central molecular column density, Arp 220
might not evolve such a ``seamless'' light profile. We conclude that
ultraluminous infrared mergers such as Arp 220 either evolve into ellipticals
with anomalous luminosity profiles, or do not produce many low-mass stars out
of their molecular gas complexes.Comment: Final refereed version. Note new title. 4 pages, 2 encapsulated color
figures, uses emulateapj.sty. Accepted to ApJL. Also available at
http://www.cv.nrao.edu/~jhibbard/Remnants/remnants.htm
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