148 research outputs found
Transfer of autocollimator calibration for use with scanning gantry profilometers for accurate determination of surface slope and curvature of state of the art x ray mirrors
X ray optics, desired for beamlines at free electron laser and diffraction limited storage ring x ray light sources, must have almost perfect surfaces, capable of delivering light to experiments without significant degradation of brightness and coherence. To accurately characterize such optics at an optical metrology lab, two basic types of surface slope profilometers are used the long trace profilers LTPs and nanometer optical measuring NOM like angular deflectometers, based on electronic autocollimator AC ELCOMAT 3000. The inherent systematic errors of the instrument s optical sensors set the principle limit to their measuring performance. Where autocollimator of a NOM like profiler may be calibrated at a unique dedicated facility, this is for a particular configuration of distance, aperture size, and angular range that does not always match the exact use in a scanning measurement with the profiler. Here we discuss the developed methodology, experimental set up, and numerical methods of transferring the calibration of one reference AC to the scanning AC of the Optical Surface Measuring System OSMS , recently brought to operation at the ALS Xray Optics Laboratory. We show that precision calibration of the OSMS performed in three steps, allows us to provide high confidence and accuracy low spatial frequency metrology and not print into measurements the inherent systematic error of tool in use. With the examples of the OSMS measurements with a state of the art x ray aspherical mirror, available from one of the most advanced vendors of X ray optics, we demonstrate the high efficacy of the developed calibration procedure. The results of our work are important for obtaining high reliability data, needed for sophisticated numerical simulations of beamline performance and optimization of beamline usage of the optics. This work was supported by the U. S. Department of Energy under contract number DE AC02 05CH1123
Simultaneous optical polarimetry and X-ray data of the near synchronous polar RX J2115-5840
We present simultaneous optical polarimetry and X-ray data of the near
synchronous polar RX J2115-5840. We model the polarisation data using the
Stokes imaging technique of Potter et al. We find that the data are best
modelled using a relatively high binary inclination and a small angle between
the magnetic and spin axes. We find that for all spin-orbit beat phases, a
significant proportion of the accretion flow is directed onto the lower
hemisphere of the white dwarf, producing negative circular polarisation. Only
for a small fraction of the beat cycle is a proportion of the flow directed
onto the upper hemisphere. However, the accretion flow never occurs near the
upper magnetic pole, whatever the orientation of the magnetic poles. This
indicates the presence of a non-dipole field with the field strength at the
upper pole significantly higher. We find that the brightest parts of the hard
X-ray emitting region and the cyclotron region are closely coincident.Comment: 9 pages, accepted for publication in MNRAS 2 March 200
X-Ray Emission and Optical Polarization of V1432 Aquilae: An Asynchronous Polar
A detailed analysis of X-ray data from ROSAT, ASCA, XMM and RXTE for the
asynchronous polar V1432 Aql along with Stokes polarimetry data from SAAO, is
presented. Power spectra from long-baseline ROSAT data show a spin period of
12150s along with several system related frequency components. However, the
second harmonic of the spin period dominates power spectrum in the XMM data.
For the optical circular polarization, the dominant period corresponds to half
the spin period. The ROSAT data can be explained as due to accretion onto two
hot spots that are not anti-podal. The variations seen in the optical
polarization and the ASCA and XMM data suggest the presence of at least three
accretion foot prints on the white dwarf surface. Two spectral models, a
multi-temperature plasma and a photo-ionized plasma model, are used for
spectral study. The RXTE PCA data are used to constrain the white dwarf mass to
1.20.1 M_odot using the multi-temperature plasma model. A strong soft
X-ray excess (<0.8 keV) in the XMM MOS data is well modeled by a blackbody
component having a temperature of 80-90 eV. The plasma emission lines seen at
6.7 and 7.0 keV are well fitted using the multi-temperature plasma model,
however an additional Gaussian is needed for the 6.4 keV line. The
multi-temperature plasma model requires a homogeneous absorber fully covering
the source and a partial absorber covering 65% of the source. The photo-ionized
plasma model, with a range of Fe column densities, gives a slightly better
overall fit and fits all emission lines. The presence of a strong blackbody
component, a spin period of 12150s, modulation of the 6.4 keV line flux with
spin period, and a very hard X-ray component suggest that V1432 Aql is a polar
with X-ray spectral properties similar to that of a soft intermediate polar.Comment: 46 pages, including 13 figures and 4 tables, To appear in The
Astrophysical Journal, 20 May 2005 issue, vol. 625, Added Report-no and
Journal-ref, no change in the text of the pape
Time-Resolved HST Spectroscopy of Four Eclipsing Magnetic Cataclysmic Variables
Time-resolved HST UV eclipse spectrophotometry is presented for the magnetic
CVs V1309 Ori, MN Hya, V2301 Oph, and V1432 Aql. Separation of the light curves
into wavebands allows the multiple emission components to be distinguished.
Photospheric hot spots are detected in V1309 Ori and V2301 Oph. The emission-
line spectra of V1309 Ori and MN Hya are unusual, with the strength of N V 1240
and N IV 1718 suggesting an overabundance of nitrogen. Three epochs of
observation of the asynchronous V1432 Aql cover ~1/3 of a 50-day lap cycle
between the white dwarf spin and binary orbit. The light curves vary from epoch
to epoch and as a function of waveband. The dereddened UV spectrum is extremely
bright and the spectral energy distribution coupled with the duration of
eclipse ingress indicate that the dominant source of energy is a hot
(T~35,000K) white dwarf. Undiminished line emission through eclipse indicates
that the eclipse is caused by the accretion stream, not the secondary star. The
hot white dwarf, combined with its current asynchronous nature and rapid
timescale for relocking, suggests that V1432 Aql underwent a nova eruption in
the past 75-150 yr. The reversed sense of asynchronism, with the primary star
currently spinning up toward synchronism, is not necessarily at odds with this
scenario, if the rotation of the magnetic white dwarf can couple to the ejecta
during the wind phase of the eruption.Comment: To appear in ApJ Part 1; 25 pages, 12 figure
Dark states of dressed Bose-Einstein condensates
We combine the ideas of dressed Bose-Einstein condensates, where an
intracavity optical field allows one to design coupled, multicomponent
condensates, and of dark states of quantum systems, to generate a full quantum
entanglement between two matter waves and two optical waves. While the matter
waves are macroscopically populated, the two optical modes share a single
photon. As such, this system offers a way to influence the behaviour of a
macroscopic quantum system via a microscopic ``knob''.Comment: 6 pages, no figur
Debye-Hueckel solution for steady electro-osmotic flow of a micropolar fluid in a cylindrical microcapillary
Analytic expressions for the speed, flux, microrotation, stress, and couple
stress in a micropolar fluid exhibiting steady, symmetric and one-dimensional
electro-osmotic flow in a uniform cylindrical microcapillary were derived under
the constraint of the Debye-Hueckel approximation, which is applicable when the
cross-sectional radius of the microcapillary exceeds the Debye length, provided
that the zeta potential is sufficiently small in magnitude. As the aciculate
particles in a micropolar fluid can rotate without translation, micropolarity
influences fluid speed, fluid flux, and one of the two non-zero components of
the stress tensor. The axial speed in a micropolar fluid intensifies as the
radius increases. The stress tensor is confined to the region near the wall of
the microcapillary but the couple stress tensor is uniform across the
cross-section.Comment: 19 page
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