13,294 research outputs found
Fluid flow analysis by a modified, white light, Lau interferometer
This paper presents a sharp focussing schlieren system based upon a modified Lau interferometer. A method of reducing the depth of focus of the system is demonstrated and the development of the system to study large fields of view by theincorporation of flexible membrane mirrors is discussed
Anti-Spoof Reliable Biometry of Fingerprints Using En-Face Optical Coherence Tomography
Optical coherence tomography (OCT) is a relatively new imaging technology which can produce high-reso- lution images of three-dimensional structures. OCT has been mainly used for medical applications such as for ophthalmology and dermatology. In this study we demonstrate its capability in providing much more re- liable biometry identification of fingerprints than conventional methods. We prove that OCT can serve se- cure control of genuine fingerprints as it can detect if extra layers are placed above the finger. This can pre- vent with a high probability, intruders to a secure area trying to foul standard systems based on imaging the finger surface. En-Face OCT method is employed and recommended for its capability of providing not only the axial succession of layers in depth, but the en-face image that allows the traditional pattern identification. Another reason for using such OCT technology is that it is compatible with dynamic focus and therefore can provide enhanced transversal resolution and sensitivity. Two En-Face OCT systems are used to evaluate the need for high resolution and conclusions are drawn in terms of the most potential commercial route to ex- ploitation
Visible spectrum extended-focus optical coherence microscopy for label-free sub-cellular tomography
We present a novel extended-focus optical coherence microscope (OCM)
attaining 0.7 {\mu}m axial and 0.4 {\mu}m lateral resolution maintained over a
depth of 40 {\mu}m, while preserving the advantages of Fourier domain OCM. Our
method uses an ultra-broad spectrum from a super- continuum laser source. As
the spectrum spans from near-infrared to visible wavelengths (240 nm in
bandwidth), we call the method visOCM. The combination of such a broad spectrum
with a high-NA objective creates an almost isotropic 3D submicron resolution.
We analyze the imaging performance of visOCM on microbead samples and
demonstrate its image quality on cell cultures and ex-vivo mouse brain tissue.Comment: 15 pages, 7 figure
Ultrahigh resolution optical coherence tomography using a superluminescent light source
A superluminescent Ti:Al2O3 crystal is demonstrated as a light source for ultrahigh resolution optical coherence tomography (OCT). Single spatial mode, fiber coupled output powers of ~40 ÎĽW can be generated with 138 nm bandwidth using a 5 W frequency doubled, diode pumped laser, pumping a thin Ti:Al2O3 crystal. Ultrahigh resolution OCT imaging is demonstrated with 2.2 ÎĽm axial resolution in air, or 1.7 ÎĽm in tissue, with >86 dB sensitivity. This light source provides a simple and robust alternative to femtosecond lasers for ultrahigh resolution OCT imaging
Direct measurement of the electron density of extended femtosecond laser pulse-induced filaments
We present direct time- and space- resolved measurements of the electron
density of femtosecond laser pulse-induced plasma filaments. The dominant
nonlinearity responsible for extended atmospheric filaments is shown to be
field-induced rotation of air molecules.Comment: 12 pages, 5 figure
A Compact Millimeter-Wavelength Fourier-Transform Spectrometer
We have constructed a Fourier-transform spectrometer (FTS) operating between
50 and 330 GHz with minimum volume (355 x260 x64 mm) and weight (13 lbs) while
maximizing optical throughput (100 sr) and optimizing the
spectral resolution (4 GHz). This FTS is designed as a polarizing
Martin-Puplett interferometer with unobstructed input and output in which both
input polarizations undergo interference. The instrument construction is simple
with mirrors milled on the box walls and one motorized stage as the single
moving element. We characterize the performance of the FTS, compare the
measurements to an optical simulation, and discuss features that relate to
details of the FTS design. The simulation is also used to determine the
tolerance of optical alignments for the required specifications. We detail the
FTS mechanical design and provide the control software as well as the analysis
code online.Comment: Submitted to Applied Optics. [Copyright 2019 Optical Society of
America]. Users may use, reuse, and build upon the article, or use the
article for text or data mining, so long as such uses are for non-commercial
purposes and appropriate attribution is maintained. All other rights are
reserve
Darwin -— an experimental astronomy mission to search for extrasolar planets
As a response to ESA call for mission concepts for its Cosmic Vision 2015–2025 plan, we propose a mission called Darwin. Its primary goal is the study of terrestrial extrasolar planets and the search for life on them. In this paper, we describe different characteristics of the instrument
High precision dynamic multi-interface profilometry with optical coherence tomography
Optical coherence tomography (OCT) has mostly been used for high speed volume imaging but its profilometry potentials have not been fully exploited. This paper demonstrates high precision (as good as ~50nm) multi-interface profilometry using a Fourier domain OCT system without special anti-vibration devices. The precision is up to two orders of magnitudes better than the depth resolution of the OCT. Detailed analysis of the precision achieved for different surfaces is presented. The multi-interface profiles are obtained as a by-product of the tomography data. OCT has advantage in speed and sensitivity at detecting rough and internal interfaces compared to conventional optical profilometry. An application of the technique to the dynamic monitoring of varnish drying on paint-like substrates is demonstrated, which provides a better understanding of the formation of surface roughness. The technique has potential benefits in the field of art conservation, coatings technology and soft matter physics
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