821 research outputs found
An optical technology study on large aperture telescopes
The difficult and crucial problem of selecting a suitable telescope concept for an advanced space observatory was examined. To this end two and four mirror telescopes were analyzed and compared. Both configurations are very practical and structurally similar. Parabolic primary and spherical primary four mirror telescope were compared with respect to their performance and the alignment sensitivities of the three correction mirrors. A 1 meter class afocal telescope system with lag angle compensation, to be used in a LIDAR experiment, was examined
Analysis and design optimization of the 1.2m X-ray telescope, volume 1
An image space analysis and optimization and a performance analysis of the telescope assembly in the presence of various alignment errors are reported. Possible tests arrangements for 1.2 m or 1.5 m diameter X-ray telescopes are elaborated
Experimental evaluation of the ring focus test for X-ray telescopes using AXAF's technology mirror assembly, MSFC CDDF Project No. H20
A test method particularly suited for X-ray telescopes was evaluated experimentally. The method makes use of a focused ring formed by an annular aperture when using a point source at a finite distance. This would supplement measurements of the best focus image which is blurred when the test source is at a finite distance. The telescope used was the Technology Mirror Assembly of the Advanced X-ray Astrophysis Facility (AXAF) program. Observed ring image defects could be related to the azimuthal location of their sources in the telescope even though in this case the predicted sharp ring was obscured by scattering, finite source size, and residual figure errors
Performance analysis of grazing incidence imaging systems
An exact expression relating the coordinates of a point on the incident ray, a point of reflection from an arbitrary surface, and a point on the reflected ray is derived. The exact relation is then specialized for the case of grazing incidence, and first order and third order systematic analyses are carried out for a single reflective surface and then for a combination of two surfaces. The third order treatment yields a complete set of primary aberrations for single element and two element systems. The importance of a judicious choice for a coordinate system in showing field curvature to clearly be the predominant aberration for a two element system is discussed. The validity of the theory is verified through comparisons with the exact ray trace results for the case of the telescope
Beyond mean-field dynamics of small Bose-Hubbard systems based on the number-conserving phase space approach
The number-conserving quantum phase space description of the Bose-Hubbard
model is discussed for the illustrative case of two and three modes, as well as
the generalization of the two-mode case to an open quantum system. The
phase-space description based on generalized SU(M) coherent states yields a
Liouvillian flow in the macroscopic limit, which can be efficiently simulated
using Monte Carlo methods even for large systems. We show that this description
clearly goes beyond the common mean-field limit. In particular it resolves
well-known problems where the common mean-field approach fails, like the
description of dynamical instabilities and chaotic dynamics. Moreover, it
provides a valuable tool for a semi-classical approximation of many interesting
quantities, which depend on higher moments of the quantum state and are
therefore not accessible within the common approach. As a prominent example, we
analyse the depletion and heating of the condensate. A comparison to methods
ignoring the fixed particle number shows that in this case artificial number
fluctuations lead to ambiguities and large deviations even for quite simple
examples.Comment: Significantly enhanced and revised version (20 pages, 20 figures
Quantum transport and localization in biased periodic structures under bi- and polychromatic driving
We consider the dynamics of a quantum particle in a one-dimensional periodic
potential (lattice) under the action of a static and time-periodic field. The
analysis is based on a nearest-neighbor tight-binding model which allows a
convenient closed form description of the transport properties in terms of
generalized Bessel functions. The case of bichromatic driving is analyzed in
detail and the intricate transport and localization phenomena depending on the
communicability of the two excitation frequencies and the Bloch frequency are
discussed. The case of polychromatic driving is also discussed, in particular
for flipped static fields, i.e. rectangular pulses, which can support an almost
dispersionless transport with a velocity independent of the field amplitude.Comment: 18 pages, 11 figur
Test method for telescopes using a point source at a finite distance
A test method for telescopes that makes use of a focused ring formed by an annular aperture when using a point source at a finite distance is evaluated theoretically and experimentally. The results show that the concept can be applied to near-normal, as well as grazing incidence. It is particularly suited for X-ray telescopes because of their intrinsically narrow annular apertures, and because of the largely reduced diffraction effects
Three-mirror space telescope, volume 2
The anastigmatic three mirror telescope for STARSAT, a space astronomy facility, was redesigned and reoptimized in order to improve the optical system and increase its versatility. A more compact system was obtained by decreasing the primary focal ratio from 2.2 to 2.0. A high performance Rowland spectrograph that uses only a total of three reflections and does not interfere with the imaging process, was successfully incorporated into the telescope so that it could be a permanent part of the system. The usefulness of this telescope concept as a high resolution coronagraph is examined
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