Over the past century there has been a dramatic increase in the demand for float glass in many fields of industry.
Usually, 10 to 30% of produced float glass is coated with various coatings for different purposes. As a consequence
quality control of the coatings is one of the most current issues during the process of float glass manufacturing.
In this work we describe a system designed for the online control of reflectivity, transmittance and color coordinates of
the coatings during the glass production process. The working principle of the system is based on the measurement of the
spectral characteristics of reflectivity and transmittance of coatings within the 400-700 nm spectrophotometer spectral
range during the online coating process.
The measurement unit consists of two microspectrometers (one for the measurements of the spectral characteristics of
the reference source, and the other for the measurements of the reflectance spectrum), illumination head (consisting of
one white 1W LED and collimating lenses), stabilized power supply, microprocessor and 18 bits precision ADC. The
use of the reference channel allows us to stabilize the intensity of the incident light up to 10-4 level. The repeatability of
the measurement of reflectivity coefficient in laboratory conditions was in range of ± 0.001. However, in the
measurements in the factory environment, due to the vibration of the glass ribbon on the conveyer, the measurement
reproducibility was about ± 0.005.
Progresses in the optical coatings and optical material fields require an increase in the sensitivity and accuracy of the
optical parameters' measurement methods and systems. In this work we describe a flexible and high-accuracy system for
measuring the main optical characteristics at 632.8 nm wavelength. The system comprises two methods: a laser ratio-metric
measurement method for absolute measurement of the transmittance and the specular reflectance, and an
integrating-sphere method for assessment of the total integrated scattering. The system utilizes an intensity stabilized He-
Ne laser as a light source. Two four-element trap detectors are used: the first for monitoring of laser power, the second
(fixed on a motorized stage) for the measurement of reflectance and transmittance, one after another. A PMT mounted to
the exit port of a 40 cm diameter integrating hemisphere, is used for measuring the total integrated scattering. A series of
measurements with several reference mirrors showed that the system is able to measure the specular reflectance with a
reproducibility of <0.005%, transmittance of 0.005% with a reproducibility <0.005%, and total integrated scattering
about 10 ppm, with a reproducibility of < 5 ppm at 2 sigma. The system allows characterizing of optical components
with diameters between 5 mm and 50 mm.
Particle Image Velocimetry (PIV) is a non-invasive, full-field optical measurement technique that has become a
dominant tool for velocity measurement of fluids and gases at both macro (traditional PIV) and micro (microPIV) scales.
In PIV experiments, the fluid under the investigation is seeded with tracer particles, which are shining under an
excitation by a properly tuned light source. The idea behind the method is to precisely register the position of
corresponding particles in two shifted instances of time and then using these records calculating particle displacements,
i.e. flow velocity. In most PIV experimental setups, illumination is performed using dual cavity pulse lasers, whose
outputs reach several hundreds mJ at short pulse lengths (tens of nano-seconds). Unfortunately, such laser systems are
very expensive and bulky. In this work, we investigate a possibility to replace the laser illumination with a high power
LED illumination, aiming towards the development of the cost effective and portable microPIV systems.
We have developed an electronic circuit, which drives LEDs with a high current over short time duration. The driver
circuit is triggered by an internal electronics of the CCD camera, and is able to produce single or double current pulses
per camera trigger. Besides, the circuit also allows i) flexible adjustment of the pulse duration (from 1 μs up to tens of
msec), ii) the time delay within pulse pairs, which is crucial for double-frame mode, and iii) time delay between the
trigger signal and current pulses.
We present experimental results of flow velocity measurements obtained using the microPIV system and the developed
illumination setup. We have investigated the flow of water, which was seeded with the spherical-polystyrene-fluorescent
particles, inside rectangular microchannels. For illumination, a LumiLED LED with a peak wavelength at 470 nm was
used at the double-illumination mode, where current pulses of up to 10 A at duration of 5 μs were achieved.
In recent years CCD manufacturers have been supplying their devices with multi-purpose abilities to manipulate the
CCD's readout pattern, where one of these versatile options is a flexible pixel binning option. The pixel binning is a
process of combining multiple pixel charges in horizontal, vertical or in both directions simultaneously, into a single
charge. The binning process positively influences to the signal-to-noise ratio, sensitivity and frame rate at the cost of
decreasing spatial resolution, which, in its turn, negatively influences to the spatial frequency response of the imaging
system (i.e. to the output image quality). The modulation transfer function (MTF) is an essential measure for
characterizing the spatial-frequency response of the array imaging system. In this work we have performed a theoretical
and experimental investigation of the MTF of CCD array in the context of the pixel binning option. We have derived a
generalized equation of the geometrical MTF for the v x h binning mode, where v and h denote the numbers of binned
pixels in vertical and horizontal directions, respectively. The MTF measurements were performed using a method, based
on the generation of laser speckle and utilizing the high resolution (1360×1024) monochrome CCD array. The MTF of
normal mode, 2×1-horizontal, 1×2 - vertical, and 2x2 quadratic binning modes were measured by employing single-slit
aperture method. CCD binning is widely used in spectroscopy, astronomy, in many image processing applications, such
as autofocus, object tracking, etc. The results of this work can be useful for designing optical systems, involving CCD
pixel binning option.
Visible photoluminescence (PL) in anodized porous Si (PS) at room temperature has opened the way to realize different types of quantum electronics devices based on silicon technology. Such devices require a strong PL intensity and a controlled shift of the PL peak on the energy scale. Porous silicon is produced by electrochemical etching of either p- or n-type crystalline silicon. Illumination is one of the most complicated parameters in PS formation, because it changes the properties of microporous as well as macroporous layers. It is necessary to illuminate the wafer during the anodization in order to create the holes required by the chemical reaction to form the PS. In this paper we present the results of the effects of illumination level during fabrication on the PL properties of p-type PS and it time degradation dynamics.
Nonlinear photoinduced absorption of hydrogenated amorphous silicon (a-Si:H) was studied by excitation spectroscopy. The experimentally obtained excitation spectra are in compliance with the spectra of unperturbed absorption in 1.2 - 3.2 eV spectral range. The applicability of the method for the absorption coefficient measurement in broad range of 1 - 105 cm-1 (1 micrometers film) is demonstrated. A proposed model of photoinduced absorption from localized states is discussed.