1,302 research outputs found
The Primordial Inflation Explorer (PIXIE): A Nulling Polarimeter for Cosmic Microwave Background Observations
The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission to
measure the gravity-wave signature of primordial inflation through its
distinctive imprint on the linear polarization of the cosmic microwave
background. The instrument consists of a polarizing Michelson interferometer
configured as a nulling polarimeter to measure the difference spectrum between
orthogonal linear polarizations from two co-aligned beams. Either input can
view the sky or a temperature-controlled absolute reference blackbody
calibrator. PIXIE will map the absolute intensity and linear polarization
(Stokes I, Q, and U parameters) over the full sky in 400 spectral channels
spanning 2.5 decades in frequency from 30 GHz to 6 THz (1 cm to 50 um
wavelength). Multi-moded optics provide background-limited sensitivity using
only 4 detectors, while the highly symmetric design and multiple signal
modulations provide robust rejection of potential systematic errors. The
principal science goal is the detection and characterization of linear
polarization from an inflationary epoch in the early universe, with
tensor-to-scalar ratio r < 10^{-3} at 5 standard deviations. The rich PIXIE
data set will also constrain physical processes ranging from Big Bang cosmology
to the nature of the first stars to physical conditions within the interstellar
medium of the Galaxy.Comment: 37 pages including 17 figures. Submitted to the Journal of Cosmology
and Astroparticle Physic
The future of space imaging. Report of a community-based study of an advanced camera for the Hubble Space Telescope
The scientific and technical basis for an Advanced Camera (AC) for the Hubble Space Telescope (HST) is discussed. In March 1992, the NASA Program Scientist for HST invited the Space Telescope Science Institute to conduct a community-based study of an AC, which would be installed on a scheduled HST servicing mission in 1999. The study had three phases: a broad community survey of views on candidate science program and required performance of the AC, an analysis of technical issues relating to its implementation, and a panel of experts to formulate conclusions and prioritize recommendations. From the assessment of the imaging tasks astronomers have proposed for or desired from HST, we believe the most valuable 1999 instrument would be a camera with both near ultraviolet/optical (NUVO) and far ultraviolet (FUV) sensitivity, and with both wide field and high resolution options
Enabling Technologies for Next Generation Ultraviolet Astrophysics, Planetary, and Heliophysics Missions
Our study sought to create a new paradigm in UV instrument design, detector technology, and
optics that will form the technological foundation for a new generation of ultraviolet missions.
This study brought together scientists and technologists representing the broad community of
astrophysicists, planetary and heliophysics physicists, and technologists working in the UV.
Next generation UV missions require major advances in UV instrument design, optics and
detector technology. UV offers one of the few remaining areas of the electromagnetic spectrum
where this is possible, by combining improvements in detector quantum efficiency (5-10x),
optical coatings and higher-performance wide-field spectrometers (5-10x), and increasing
multiplex advantage (100-1000x).
At the same time, budgets for future missions are tightly constrained. Attention has begun to turn
to small and moderate class missions to provide new observational capabilities on timescales that
maintain scientific vitality. Developments in UV technology offer a comparatively unique
opportunity to conceive of small (Explorer) and moderate (Probe, Discovery, New Millennium)
class missions that offer breakthrough science.
Our study began with the science,
reviewing the breakthrough science
questions that compel the development of
new observational capabilities in the next
10-20 years. We invented a framework for
highlighting the objectives of UV
measurement capabilities: following the
history of baryons from the intergalactic
medium to stars and planets. In
astrophysics, next generation space UV missions will detect and map faint emission and
tomographically map absorption from intergalactic medium baryons that delineate the structure
of the Universe, map the circum-galactic medium that is the reservoir of galaxy-building gas,
map the warm-hot ISM of our Galaxy, explore star-formation within the Local group and beyond,
trace gas in proto-planetary disks and extended atmospheres of exoplanets, and record the
transient UV universe. Solar system planetary atmospheric physics and chemistry, aurorae,
surface composition and magnetospheric environments and interactions will be revealed using
UV spectroscopy. UV spectroscopy may even detect life on an exoplanet.
Our study concluded that with UV technology developments within reach over the next 5-
10 years, we can conceive moderate-class missions that will answer many of the compelling
science questions driving the field.
We reviewed the science measurement requirements for these pioneering new areas and
corresponding technology requirements. We reviewed and evaluated the emerging technologies,
and developed a figure of merit based on potential science impact, state of readiness, required
investment, and potential for highly leveraged progress in a 5-10 year horizon. From this we
were able to develop a strategy for technology development. Some of this technology
development will be subject to funding calls from federal agencies. A subset form a portfolio of
highly promising technologies that are ideal for funding from a KISS Development Program.
One of our study’s principal conclusions was that UV detector performance drives every aspect
of the scientific capability of future missions, and that two highly flexible detector technologies
were at the tipping point for major breakthroughs. These are Gen-2 borosilicate Atomic Layer
Deposition (ALD) coated microchannel plate detectors with GaN photocathodes, and ALDantireflection
(AR) coated, delta-doped photon-counting CCD detectors. Both offer the potential
for QE>50% combined with large formats and pixel counts, low background, and sky-limited
photon-counting performance over the 100-300 nm band. Ramped AR coatings for
spectroscopic detectors could achieve QE’s as high as 80%!
A second conclusion was that UV coatings are on the threshold of a major breakthrough. UV
coatings permeate every aspect of telescope and instrument design. Efficient, robust, ultra-thin
and highly uniform reflective coatings applied with Atomic Layer Deposition (ALD) offer the
possibility of high-performance, wide-field, highly-multiplexed UV spectrometers and a broadband
reach covering the scientifically critical 100-120 nm range (home of 50% of all atomic and
molecular resonance lines). Our study concluded that UV coating advances made possible by
ALD is the principle technology advance that will enable a joint UV-optical general
astrophysics and exoEarth imaging flagship mission.
A third conclusion was that the revolution in micro- and nano-fabrication technology offers a
cornucopia of new possibilities for revolutionary UV technology developments in the near future.
An immediate example is the application of new microlithography techniques to patterning UV
diffraction gratings that are highly efficient and designed to enable wide-field, high-resolution
spectroscopy. These techniques could support the development of new detectors that could
discriminate optical and UV photons and potentially energy-resolving detection.
Relatively modest investments in technology development over the next 5-10 years could
provide advances in detectors, coatings, diffractive elements, and filters that would result
in an effective increase in science capability of 100-1000!
The study brought together a diverse community, led to many new ideas and collaborations, and
brought cohesion and common purpose to UV practitioners. This will have a lasting and positive
impact on the future of our field
The design and optimization of synchronization sequence for Ultraviolet communication
In the ultraviolet (UV) scattering communication, the received signals
exhibit the characteristics of discrete photoelectrons due to path loss. The
synchronization is based on maximum Pulse Number-Sequence correlation problem.
First of all, the accuracy of synchronization is vital to channel estimation
and decoding. This article focuses on improving synchronization accuracy by
designing and optimizing synchronization sequences. As for the maximum Pulse
Number-Sequence correlation problem, it is assumed that the correlation values
satisfy the Gaussian distribution and their mathematical expectation, variance
and covariance are derived to express the upper bound of synchronization
offset. The synchronization sequence we designed has two equilong RANDOM parts
(Symbols meet Bernoulli distribution with equal probability.) and a
part between them with as its
proportion of entire sequence. On the premise of ensuring the synchronization
reliability, the synchronization deviation can be reduced by optimizing .
There are simulation experiments to verify correctness of the derivation,
reasonableness of the hypothesis and reliability of optimization. Compared with
equilong random sequence, the synchronization accuracy of the optimized
synchronization sequence is significantly improved
The observation of Extensive Air Showers from an Earth-Orbiting Satellite
In this paper we review the main issues that are relevant for the detection
of Extensive Air Showers (EAS) from space. EAS are produced by the interaction
of Ultra-High Energy Cosmic Particles (UHECP) with the atmosphere and can be
observed from an orbiting telescope by detecting air fluorescence UV light. We
define the requirements and provide the main formulas and plots needed to
design and optimize a suitable telescope. We finally estimate its expected
performances in ideal conditions.Comment: 24 pages, 10 figures; submitted to Astroparticle Physics 27 pages, 14
figures; major revision; added new figures and sections; typos fixed. arXiv
admin note: substantial text overlap with arXiv:0810.571
Effects of Turbulence Induced Scattering on Underwater Optical Wireless Communications
This paper presents a comprehensive description of the relative effect of
optical underwater turbulence in combination with absorption and scattering.
Turbulence induced scattering is shown to cause and increase both spatial and
temporal spreading at the receiver plane. It is also demonstrated that the
relative impact of turbulence on a received signal is lower in a highly
scattering channel. Received intensity distributions are presented confirming
that fluctuations in received power from this method follow the commonly used
Log-Normal fading model. The impact of turbulence induced scattering on maximum
achievable data rate in the underwater channel is investigated.Comment: 9 pages, 10 figures and 3 table
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