Based on technological achievements artificial lighting is changing all over the world. The involved changes, mainly driven by minimizing electric energy consumption, imply the replacement of almost every traditional light source by light- emitting diodes (LEDs) in almost every level of human activities. An incipient rapid transition is being carried out on a massive scale since a decade; this fact is still cause of concern and controversies from some researchers, experts, professionals, associations and the public in general. Several characteristics of the new lighting sources including LED screens have been proven to affect individual visual and non-visual health (i.e., digital eye syndrome and disruption of circadian rhythms) as well as general well- being (threats to ecosystems); furthermore, there are claims that regulations should be rethought. This paper provides a panoramic view of several aspects of the problematic posed by new artificial light sources. The main focus of this preliminary work is aimed at presenting and discussing the spectral characteristics of representative cases of commercial domestic lamps (incandescent, fluorescent and LED units) and screens (cold cathode fluorescent and LED units) which are ubiquitous in everyday life of Argentinian society. Given that some sources have important spectral content in the phototoxic region (400- 500 nm), palliative often suggested strategies employing transparent and pigmented commercially available filters as well as free software, were evaluated. Results show that the studied strategies perform within a large range of attenuation in the way they block short wavelengths.
In this work we introduce a new approach to fabricate under SiN platform a small foot print power splitter. The proposed strategy of design is based on the well-known simplified coherent coupling. The sensibility of design parameters are also analyzed and discussed in this paper. By this approach very compact device can be designed and it opens a new avenue to improve and enhance the performance of integrated devices developed under silicon nitride scheme.
In this paper, we propose a new sensing topology based on a differential power analysis, using an array of photonic sensors. The system structure is composed of a 1x4 balanced power divider, three Bragg gratings, and a reference branch. In particular, we present an analysis of the individual sensing parameters of the Bragg gratings, as well as the procedure to be followed in order to optimise the design parameters of the sensing system. The designs were verified with simulations by different numerical methods. Finally, a substantial reduction of the detection limit is demonstrated by easy-to-implement signal post-processing.
Femtosecond laser pulse systems allows to modify in a precise and permanent way the optical properties of a transparent materials. This process enables the direct writing of guiding structures in materials, commonly known as waveguides, which are the base for optical circuit fabrication. It is our interest to study the main characteristics of the waveguides manufactured by the laser micromachining technique. Here, an analysis of the resulting refractive index profile has been carried out. This characteristic is essential for the design and simulation of integrated optical circuits. In particular we have developed our research on the study of light coupling in a pair of type II waveguides made in Lithium Niobate (LiNbO3). These experimental backgrounds provide us with elements to adjust and test the retrieved profile. Taking into account different distance between tracks and writing energies, it is well known that the coupling length changes and the coupling ratio too. Then this study allows us to reconstruct the refractive index profile according to its manufacturing conditions. Modeling of the refractive index distribution profile is a key parameter to perform beam propagation mode simulations (BPM) to achieve more realistic results. So, by means of this method it is possible to obtain a general procedure to describe the characteristics of these kinds of waveguides. As a model test, integrated waveguides were built to corroborate their light coupling. In a first stage it is designed through BPM simulations then it is manufactured in an X-cut LiNbO3 crystal in order to check its operation according to the simulations carried out.
An optical fiber ring resonator (OFRR), a wavelength sensor for testing a single-mode laser system in a wide range of temperature, is presented. We will show that it is possible to calibrate, in relative form, a scale of wavelength, to determine, accurately enough, a thermally induced laser detuning, using the free spectral range of an OFRR. The optical circuit was constructed using 2 × 2 (50/50) optical fiber coupler obtaining an OFRR of 10-cm ring radius. A single-mode diode laser system has been launched into the OFRR, and different experiments have been performed. We tested the OFRR performance, considering fluctuations in the laser wavelength caused by small temperature instabilities, measuring the output intensity from the ring resonator. Theoretical simulations and experimental results were in agreement with the expected behavior. Furthermore, OFRR systems can be used as an excellent control tool to test the wavelength stability for a narrowband laser diode and act as a part of a control system.
The synthesis and study of optical properties of copper nanoparticles are of great interest since they are
applicable to different areas such as catalysis, lubrication, conductive thin films and nanofluids. Their optical properties
are governed by the characteristics of the dielectric function of the metal, its size and environment.
The study of the dielectric function with radius is carried out through the contribution of free and bound
electrons. The first one is corrected for size using the modification of the damping constant. The second one takes into
consideration the contribution of the interband transitions from the d-band to the conduction band, considering the larger spacing between electronic energy levels as the particle decreases in size below 2 nm.
Taking into account these specific modifications, it was possible to fit the bulk complex dielectric function, and
consequently, determine optical parameters and band energy values such as the coefficient for bound electron
contribution Qbulk = 2 x 1024, gap energy Eg = 1.95 eV, Fermi energy EF = 2.15 eV and damping constant for bound electrons γb = 1.15 x 1014 Hz.
The fit of the experimental extinction spectra of the colloidal suspensions obtained by 500 μJ ultrashort pulse
laser ablation of solid target in water and acetone, reveals that the nanometric and subnanometric particles have a Cu-
Cu2O structure due to an oxidation reaction during the fabrication. The results were compared with those obtained by AFM, observing a very good agreement between the two techniques, showing that Optical Extinction Spectroscopy (OES) is a good complementary technique to standard electron microscopy.
In this work we have studied the fragmentation of gold nanoparticles (NPs) after generation by femtosecond laser
ablation of a solid target in deionized water. The fragmentation process was carried out using two different types of
radiation: direct ultra-fast pulses and super-continuum radiation focused in the colloidal solution. In the former case, IR
pulses were applied both in low and high fluences regime, while in the latter, super-continuum was generated by an
external sapphire crystal. In this last case, to assess the effects of the different spectral bands present in the super-continuum
for fragmentation, we have determined different efficiency regions. From the analysis of optical extinction
spectra and Transmission Electron Microscopy (TEM) histograms we can conclude that the main mechanism is linear
absorption in the visible region. Likewise, the super-continuum generated in water during fragmentation resulted more
efficient than that obtained externally by the sapphire crystal. This fact can be attributed to the broadening of the water
continuum band originated due to large intensity used for generation. TEM and Small Angle X-ray Scattering (SAXS)
measurements support the results found from optical extinction spectroscopy.
Optical single backscattering spectroscopy can be used for sizing particles suspended in aqueous solution. In this work, we present results of backscattering spectroscopy applied to the determination of radii of calibrated spherical latex microparticles when a beam of white light is incident on the sample. From Mie calculations and Fourier analysis, we can determine the radius of particles covering the range between 0.5 and 12 µm for monomodal samples, with a mean error of 0.7 µm. To improve the accuracy, a correlation algorithm is applied that reduces the uncertainty in more than an order of magnitude and compares to the traceable error given by the manufacturer. The method can be also applied to bimodal and trimodal samples, allowing the separation of different size components.
A low cost portable spectroradiometer able to operate in the 4 bands of the satellite system Landsat MSS was developed. The radiometer was designed to measure the spectral reflectance of spatially extended targets. Spectral bands were selected with 10 nm bandwidth filters. Measurements were made during 2003, from seedtime to harvest, on an experimental plot of wheat. The culture was divided in parcels that received different treatments (seed variety, fertilizer, herbicide and fungicide). Weekly measurements with the detector at nadir and the sun near midday were made. As result of the spectral measurements of reflectance, the normalized difference vegetation index (NDVI) was calculated. As a comparison, LAI, chlorophyll concentration and diverse gravimetric determinations, were carried out. The results were analyzed by means of statistical techniques and showed a good correlation between the optical index and the culture variables. In the future the geometry of the measurement will be improved to reduce the effect of the canopy and other channel in the near infrared will be added to distinguish water and nitrogen stress.
Optical backscattering spectroscopy offers instrumental advantages over fixed wavelength multiangle scattering measurements. We present results of backscattering spectroscopy of calibrated spherical latex micro particles in aqueous solution when a beam of white light is incident on the sample. From Mie calculations and Fourier analysis, the radius of the particles can be retrieved, both in monomodal (single particle size present) and bimodal (two particle size present) samples.
This work continues with the development of a non-dispersive UV optical sensor for stack emissions for SO2 and NO2. These gases are among the most important ones in the emissions of the petrochemical industry. The NDUV consists of three optical channels sensing different spectral regions: 300 nm for SO2, 380 nm for NO2 and 320 nm used as a common reference. Each channel has an interference filter centered at each channel's wavelength, and a photodiode with control electronics. Calibration curves and the effect of cross interference on concentration measurements of these gases are shown.
12 Non-dispersive analyzers have been used for measurement of gases for many years and were recently introduced as on-line meters for continuous stack emission measurements in industrial plants. SO2 and NO2 are among the most important gases in the emissions of the petrochemical industry. The development of a UV-visible meter for these gases is presented. It consists of three optical channels sensing different spectral regions: 300 nm for SO2, 380 nm for NO2 and 320 nm used as a common reference. Each channel has an interference filter of 10 nm bandwidth centered at each channel's wavelength. Each filter is followed by a photodiode and its electronics which are housed in a single compartment with no moving parts. An incandescent lamp with high output in the UV region was selected and mounted on the opposite side of the stack by appropriate flanges. The equipment was designed to measure in the range between 0 and 500 ppmv with a resolution of about 2 ppmv. Performance parameters like signal stability, dark current, detection limit and calibration curves are shown.
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