1,720,963 research outputs found
Thickness measurement of transparent platesby a self-mixing interferometer
No full textWe introduce a technique to measure transparent glass slab thickness. It employs a very simple setup combining two
interferometers: a forward-going beam scheme and a self-mixing readout of the beam reflected back to the laser
source. Interestingly, the difference of the two readouts provides a quantity related to thickness measurement,
irrespective of refractive index. We demonstrate this method using samples on a range of thickness from 30 to
1000 μm
Application of Delayed Optical Feedback to the Simultaneous Measurement of Index of Refraction and Thickness of Optical Slabs
No full textA new method for the measurement of thickness d and index of refraction n of transparent slabs is presented. The method is based on the interferometric measurement of the optical path-length read by a laser beam upon passing through the slab. Optical path-length is a function of angle of incidence , and we measure it by rotating the slab of =±60 deg respect to normal incidence. By fitting the function with an analytical expression so as to minimize a suitable error function, we are able to determine d in a range from a few micron to 1000-micron with typical accuracy ±2%, and n in a range 1.4 to 2.2 with typical accuracy ±0.05.
The measurement is carried out by a Self-Mixing interferometer using the delayed optical feedback of light propagated through the sample, up to a remote reflector and back, by retracing the rays to the laser source. The monitor photodiode on the rear mirror of the laser senses the interferometric signal.
A variant of method is replacing the remote reflector with a photodiode, whose front surface acts as the reflector while it detects the propagated beam superposed to a double reflected contribution at the slab walls, thus supplementing the self-mixing interferometer with a conventional, forward-going shear interferometer. This simplify the signal processing and improves accuracy
Self-Mix Interferometer to Measure Transparent Plates Thickness and Index of Refraction
No full textWe present a new method to measure thickness and
index of refraction of glass windows and slab, typically from a
few micrometers to 1000 micrometers and over. We use a very
simple setup yielding two optical phase shift readouts: one from
a self-mixing interferometer based on the beam crossing the
specimen, going to an external mirror and back to the laser
retracing the path, and one based on a conventional, forwardgoing
shear interferometer based on the double reflection at the
slab walls. We show that, interestingly and unique to our
method, the difference of the two phase shift readouts provides
the thickness measurement, independent from refractive index.
We then go back to one of the two readouts to solve for the index
of refraction also. We present the experimental arrangement
along with the theoretical derivation of the phase shift involved,
and discuss the sources of errors and their impact on the
measurement accuracy and precision. Experimental data show a
repeatability of +/-1% in thickness and +/-0.1 in index of
refraction, with a 825-nm laser diode emitting 5 mW. The
method looks interesting as it requires very little components, is
compact, and can be used with sources at different wavelength
as well as state of polarization
Uniformity of Concentration Factor and BFL in Microlens Array for Image Detectors Applications
No full textWe use an array of polymer microlenses spatially matched to an array of SPADs (Single Photon Avalanche Detector) to mitigate the loss of sensitivity due to the area fill-factor. The lens array is fabricated by polymer casting in a photoresist replica mold. We report results about reproducibility of concentration factor and back focal length within an individual 32x32 array. At a C factor of 35 and a focal length F=40 μm, the spread of concentration is < 6%, and the spread of BFL is <0.5 μm
RECUPERO DEL FILL-FACTOR IN RIVELATORI AD IMMAGINESPAD MEDIANTE MATRICI DI MICRO-LENTI
Full text linkUsing an array of 32x32 plano-convex micro-lenses, fabricated by co-polymer casting in a
photoresist replica mold, we achieve substantial recovery of the fill-factor loss in a SPADs
(Single Photon Avalanche Detectors) array of 32x32 pixels, 50-μm pitch, up to a factor of 38
Banco ottico per la caratterizzazione di matrici di microlenti
Full text linkWe describe in the following an Optical Test Bench suitable to measure both Concentration
and Back Focal Length of optical microlens arrays. Individual lens within an array can be
characterized without array repositioning. The Optical Test Bench is easy to use and PCcontrolled.
The reproducibility achieved is better than 0.15% for Concentration and less than
300nm for Back Focal Length
SPAD-Array Photoresponse is Increased by a Factor 35 by use of a Microlens Array Concentrator
No full textUsing an array of 32x32 plano-convex microlenses, fabricated by co-polymer casting in a photoresist replica mold, we have been able to increase the detection sensitivity of a SPAD (Single Photon Avalanche Detector) array of 32x32 pixels, 50-μm pitch, up to a factor of 3
Uniformity of Concentration Factor and Back Focal Length in Molded Polymer Microlens Arrays
No full textAn array of polymer microlenses, made of 32x32 individual elements spaced by a 50-μm pitch, is used in connection to an array of 32x32 6-μm diameter SPADs (Single Photon Avalanche Detector), with the aim of mitigating the loss in sensitivity due to the area fill-factor. The lens array is fabricated by polymer casting in a photoresist replica mold. Results about repeatability of concentration factor and back focal length are reported. At
C= 35 and a focal length F=40 μm, the spread of concentration is < 6%, and that of BFL is <0.5 μm
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
