348 research outputs found
Superfluid turbulence from quantum Kelvin wave to classical Kolmogorov cascades
A novel unitary quantum lattice gas algorithm is used to simulate quantum
turbulence of a BEC described by the Gross-Pitaevskii equation on grids up to
5760^3. For the first time, an accurate power law scaling for the quantum
Kelvin wave cascade is determined: k^{-3}. The incompressible kinetic energy
spectrum exhibits very distinct power law spectra in 3 ranges of k-space: a
classical Kolmogorov k^{-5/3} spectrum at scales much greater than the
individual quantum vortex cores, and a quantum Kelvin wave cascade spectrum
k^{-3} on scales of order the vortex cores. In the semiclassical regime between
these two spectra there is a pronounced steeper spectral decay, with
non-universal exponent. The Kelvin k^{-3} spectrum is very robust, even on
small grids, while the Kolmogorov k^{-5/3} spectrum becomes more and more
apparent as the grids increase from 2048^3 grids to 5760^3.Comment: 4 pages, 2 figure
Wavelength-independent coupler from fiber to an on-chip cavity, demonstrated over an 850nm span
A robust wide band (850 nm) fiber coupler to a whispering-gallery cavity with ultra-high quality factor is experimentally demonstrated. The device trades off ideality for broad-band, efficient input coupling. Output coupling efficiency can remain high enough for practical applications wherein pumping and power extraction must occur over very broad wavelength spans
Yb-doped glass microcavity laser operation in water
A ytterbium-doped silica microcavity laser demonstrates stable laser emission while completely submerged
in water. To our knowledge, it is the first solid-state laser whose cavity mode interacts with water. The device
generates more than 2 ÎĽW of output power. The laser performance is presented, and low-concentration biosensing
is discussed as a potential application
30-nm wavelength conversion at 10 Gbit/s by four-wave mixing in a semiconductor optical amplifier
Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is currently the only available strictly transparent wavelength-conversion technique, which is not penalized by phase matching. The span of the conversion is limited primarily by conversion efficiency and signal-to-noise (SNR) issues, both of which are expected to improve with the use of longer SOAs. In this paper, we demonstrate significantly enhanced performance of long converters in a system experiment at 10 Gbit/s. The experiment shows for the first time, to our knowledge, that FWM wavelength down-conversions can span the full gain bandwidth of erbium-doped fiber amplifiers
Wavelength conversion at 10 Gb/s by four-wave mixing over a 30-nm interval
We show that the use of a long semiconductor optical amplifier increases the error-free conversion interval of a four-wave mixing (FWM)-based wavelength converter. 30-nm wavelength down-conversion and 15-nm up-conversion have been obtained at 10 Gb/s. This result is a significant improvement over the previous best performance of a FWM-based wavelength converter and suggests that the full erbium-doped fiber amplifier bandwidth can be covered with FWM wavelength converters
A novel technique for the direct determination of carrier diffusion lengths in GaAs/AlGaAs heterostructures using cathodoluminescence
A new technique for determining carrier diffusion lengths
in direct gap semiconductors by cathodoluminescence measurement
is presented. Ambipolar diffusion lengths are
determined for GaAs quantum well material, bulk GaAs,
and Al_xGa_(1-x)As with x up to 0.38. A large increase in
the diffusion length is found as x approaches 0.38 and is
attributed to an order of magnitude increase in lifetime
On-Chip, Ultra-Low Threshold Yb Silica Laser
A novel Yb:SiO_2 fiber-coupled laser on a silicon chip was fabricated using a solution-gel process. We report a record-low pump threshold of 2 ÎĽW, and discuss the practical advantages of Yb microlasers
Spectral and dynamic characteristics of buried-heterostructure single quantum well (Al,Ga)As lasers
We demonstrate that, as predicted, (Al,Ga)As single quantum well (SQW) lasers have substantially narrower spectral linewidths than bulk double-heterostructure lasers. We have observed a further major reduction (>3Ă—) in the linewidth of these SQW lasers when the facet reflectivities are enhanced. This observation is explained theoretically on the basis of the very low losses in coated SQW lasers and the value of the spontaneous emission factor at low threshold currents. We also report on the modulation frequency response parameter of these SQW lasers
Cooling of a micro-mechanical oscillator using radiation pressure induced dynamical back-action
Cooling of a 58 MHz micro-mechanical resonator from room temperature to 11 K
is demonstrated using cavity enhanced radiation pressure. Detuned pumping of an
optical resonance allows enhancement of the blue shifted motional sideband
(caused by the oscillator's Brownian motion) with respect to the red-shifted
sideband leading to cooling of the mechanical oscillator mode. The reported
cooling mechanism is a manifestation of the effect of radiation pressure
induced dynamical backaction. These results constitute an important step
towards achieving ground state cooling of a mechanical oscillator.Comment: accepted for publication (Phys. Rev. Lett.
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