551 research outputs found
Index to NASA Tech Briefs, 1975
This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs
Optical Random Riemann Waves in Integrable Turbulence
We examine integrable turbulence (IT) in the framework of the defocusing
cubic one-dimensional nonlinear Schr\"{o}dinger equation. This is done
theoretically and experimentally, by realizing an optical fiber experiment in
which the defocusing Kerr nonlinearity strongly dominates linear dispersive
effects. Using a dispersive-hydrodynamic approach, we show that the development
of IT can be divided into two distinct stages, the initial, pre-breaking stage
being described by a system of interacting random Riemann waves. We explain the
low-tailed statistics of the wave intensity in IT and show that the Riemann
invariants of the asymptotic nonlinear geometric optics system represent the
observable quantities that provide new insight into statistical features of the
initial stage of the IT development by exhibiting stationary probability
density functions
On the Localized superluminal Solutions to the Maxwell Equations
In the first part of this article the various experimental sectors of physics
in which Superluminal motions seem to appear are briefly mentioned, after a
sketchy theoretical introduction. In particular, a panoramic view is presented
of the experiments with evanescent waves (and/or tunneling photons), and with
the "Localized superluminal Solutions" (SLS) to the wave equation, like the
so-called X-shaped waves. In the second part of this paper we present a series
of new SLSs to the Maxwell equations, suitable for arbitrary frequencies and
arbitrary bandwidths: some of them being endowed with finite total energy.
Among the others, we set forth an infinite family of generalizations of the
classic X-shaped wave; and show how to deal with the case of a dispersive
medium. Results of this kind may find application in other fields in which an
essential role is played by a wave-equation (like acoustics, seismology,
geophysics, gravitation, elementary particle physics, etc.). This e-print, in
large part a review, was prepared for the special issue on "Nontraditional
Forms of Light" of the IEEE JSTQE (2003); and a preliminary version of it
appeared as Report NSF-ITP-02-93 (KITP, UCSB; 2002). Further material can be
found in the recent e-prints arXiv:0708.1655v2 [physics.gen-ph] and
arXiv:0708.1209v1 [physics.gen-ph]. The case of the very interesting (and more
orthodox, in a sense) subluminal Localized Waves, solutions to the wave
equations, will be dealt with in a coming paper. [Keywords: Wave equation; Wave
propagation; Localized solutions to Maxwell equations; Superluminal waves;
Bessel beams; Limited-dispersion beams; Electromagnetic wavelets; X-shaped
waves; Finite-energy beams; Optics; Electromagnetism; Microwaves; Special
relativity]Comment: LaTeX paper of 37 pages, with 20 Figures in jpg [to be processed by
PDFlatex
The goldstone real-time connected element interferometer
Connected element interferometry (CEI) is a technique of observing a celestial radio source at two spatially separated antennas and then interfering the received signals to extract the relative phase of the signal at the two antennas. The high precision of the resulting phase delay data type can provide an accurate determination of the angular position of the radio source relative to the baseline vector between the two stations. This article describes a recently developed connected element interferometer on a 21-km baseline between two antennas at the Deep Space Network's Goldstone, California, tracking complex. Fiber-optic links are used to transmit the data to a common site for processing. The system incorporates a real-time correlator to process these data in real time. The architecture of the system is described, and observational data are presented to characterize the potential performance of such a system. The real-time processing capability offers potential advantages in terms of increased reliability and improved delivery of navigational data for time-critical operations. Angular accuracies of 50-100 nrad are achievable on this baseline
LIDAR sensing of the atmosphere: application to CO2 detection
Znalost o prostorovém rozložení, koncentraci a zdrojích CO2 v atmosféře je klíčová k pochopení přírodního cyklu oxidu uhličitého, k předpovědi vývoje a vlivu CO2 na klimatické změny. Tato práce se zabývá problematikou optického dálkového snímání za použití LIDAR (Light Detection and Ranging) systému. Obsahuje potřebné teoretické znalosti o LIDAR systému, použití a principy. Z mnoha aplikací využívající LIDAR je v této práci nastíněno provedení a měření pomocí DIAL (Differential Absorption LIDAR) systému určeného k určení koncentrace CO2 v atmosféře, tak i využití dalších aktivních či pasivních způsobů snímání CO2.Knowledge of the spatial distribution, concentration and sources of atmospheric CO2 is a key factor for understanding of the carbon natural cycle, predicting evolution and the impact of carbon dioxide on climate changes. This work deals with optical remote sensing using LIDAR (Light Detection and Ranging). It contains necessary theoretical background of LIDAR system, the use and principles. LIDAR is used in many applications. The application, realization and measurement of concentration CO2 in the atmosphere with DIAL (Differential Absorption LIDAR) are outlined and also the use of other active and passive sensing techniques of CO2.
Spectral compression of single photons
Photons are critical to quantum technologies since they can be used for
virtually all quantum information tasks: in quantum metrology, as the
information carrier in photonic quantum computation, as a mediator in hybrid
systems, and to establish long distance networks. The physical characteristics
of photons in these applications differ drastically; spectral bandwidths span
12 orders of magnitude from 50 THz for quantum-optical coherence tomography to
50 Hz for certain quantum memories. Combining these technologies requires
coherent interfaces that reversibly map centre frequencies and bandwidths of
photons to avoid excessive loss. Here we demonstrate bandwidth compression of
single photons by a factor 40 and tunability over a range 70 times that
bandwidth via sum-frequency generation with chirped laser pulses. This
constitutes a time-to-frequency interface for light capable of converting
time-bin to colour entanglement and enables ultrafast timing measurements. It
is a step toward arbitrary waveform generation for single and entangled
photons.Comment: 6 pages (4 figures) + 6 pages (3 figures
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