Fabry-Pérot (FP) polymer film sensors exhibit small element sizes, high acoustic sensitivity, transparency and flat frequency response to enable high resolution 3D photoacoustic (PA) imaging in backward mode. However, conventional raster scan interrogation can result in slow data acquisition (several min for 3D images) compared to parallelized piezoelectric detector arrays. To address this limitation, parallelization using a camera-based readout of FP sensors is investigated. This approach requires the optical thickness of the polymer spacer to be sufficiently uniform over the scan area to obtain high acoustic sensitivity for all active elements. Since the deposition of passive polymer layers with sufficient homogeneity of thickness is challenging, the use of electro-optically (EO) or piezoelectric (PE) tunable polymer film spacers is investigated. The spacers are sandwiched between two dielectric mirrors and transparent electrodes to form an FP sensor. In this work, spin coated guest-host systems consisting of EO chromophores (2-methyl-4-nitroaniline) embedded in a PMMA matrix, and thermally evaporated PE film spacers (PVDF) were examined. Both systems were electrically poled using a corona discharge. The optical transfer function, the transmission spectrum of the excitation passband from 600 nm to 1100 nm and the tuning range of the FP sensors were determined. Furthermore, the detection of PA waves was demonstrated. Tunable FP sensors in conjunction with camera-based interrogation techniques have the potential to provide 3D image acquisition times on the order of seconds.
Urban air pollution causes deleterious effects on human health and the environment. To meet stringent standards imposed by the European Commission, advanced measurement methods are required. Remote sensing techniques, such as light detection and ranging (LiDAR), can be a valuable option for evaluating particulate matter (PM), emitted by vehicles in urban traffic, with high sensitivity and in shorter time intervals. Since air quality problems persist not only in large urban areas, a measuring campaign was specifically performed in a suburban area of Crotone, Italy, using both a compact LiDAR system and conventional instruments for real-time vehicle emissions monitoring along a congested road. First results reported in this paper show a strong dependence between variations of LiDAR backscattering signals and traffic-related air pollution levels. Moreover, time-resolved LiDAR data averaged in limited regions, directly above conventional monitoring stations at the border of an intersection, were found to be linearly correlated to the PM concentration levels with a correlation coefficient between 0.75 and 0.84.
Particulate matter (PM), emitted by vehicles in urban traffic, can greatly affect environment air quality and have
direct implications on both human health and infrastructure integrity. The consequences for society are relevant
and can impact also on national health. Limits and thresholds of pollutants emitted by vehicles are typically
regulated by government agencies. In the last few years, the interest in PM emissions has grown substantially
due to both air quality issues and global warming. Lidar-Dial techniques are widely recognized as a costeffective
alternative to monitor large regions of the atmosphere. To maximize the effectiveness of the
measurements and to guarantee reliable, automatic monitoring of large areas, new data analysis techniques are
required. In this paper, an original tool, the Universal Multi-Event Locator (UMEL), is applied to the problem of
automatically indentifying the time location of peaks in Lidar measurements for the detection of particulate
matter emitted by anthropogenic sources like vehicles. The method developed is based on Support Vector
Regression and presents various advantages with respect to more traditional techniques. In particular, UMEL is
based on the morphological properties of the signals and therefore the method is insensitive to the details of the
noise present in the detection system. The approach is also fully general, purely software and can therefore be
applied to a large variety of problems without any additional cost. The potential of the proposed technique is
exemplified with the help of data acquired during an experimental campaign in the field in Rome.
Recently surveying large areas in an automatic way, for early detection of harmful chemical agents, has become a strategic objective of defence and public health organisations. The Lidar-Dial techniques are widely recognized as a cost-effective alternative to monitor large portions of the atmosphere but, up to now, they have been mainly deployed as ground based stations. The design reported in this paper concerns the development of a Lidar-Dial system compact enough to be carried by a small airplane and capable of detecting sudden releases in air of harmful and/or polluting substances. The proposed approach consists of continuous monitoring of the area under surveillance with a Lidar type measurement. Once a significant increase in the density of backscattering substances is revealed, it is intended to switch to the Dial technique to identify the released chemicals and to determine its concentration. In this paper, the design of the proposed system is described and the simulations carried out to determine its performances are reported. For the Lidar measurements, commercially available Nd- YAG laser sources have already been tested and their performances, in combination with avalanche photodiodes, have been experimentally verified to meet the required specifications. With regard to the DIAL measurements, new compact CO2 laser sources are being investigated. The most promising candidate presents an energy per pulse of about 50 mJ typical, sufficient for a range of at least 500m. The laser also provides the so called "agile tuning" option that allows to quickly tune the wavelength. To guarantee continuous, automatic surveying of large areas, innovative solutions are required for the data acquisition, self monitoring of the system and data analysis. The results of the design, the simulations and some preliminary tests illustrate the potential of the chosen, integrated approach.
In the last decades, atmospheric pollution in urban and industrial areas has become a major concern of both developed and developing countries. In this context, surveying relative large areas in an automatic way is an increasing common objective of public health organisations. The Lidar-Dial techniques are widely recognized as a cost-effective approach to monitor large portions of the atmosphere and, for example, they have been successful applied to the early detection of forest fire. The studies and preliminary results reported in this paper concern the development of an integrated Lidar-Dial system able to detect sudden releases in air of harmful and polluting substances. The propose approach consists of continuous monitoring of the area under surveillance with a Lidar type measurement (by means of a low cost system). Once a significant increase in the density of a pollutant is revealed, the Dial technique is used to identify the released chemicals. In this paper, the specifications of the proposed station are discussed. The most stringent requirement is the need for a very compact system with a range of at least 600-700 m. Of course, the optical wavelengths must be in an absolute eye-safe range for humans. A conceptual design of the entire system is described and the most important characteristic of the main elements are provided. In particular the capability of the envisaged laser sources, Nd:YAG and CO2 lasers, to provide the necessary quality of the measurements is carefully assessed. Since the detection of dangerous substances must be performed in an automatic way, the monitoring station will be equipped with an adequate set of control and communication devices for independent autonomous operation. The results of the first preliminary tests illustrate the potential of the chosen approach.
Lidar and dial are well established methods to explore the atmosphere. Different groups have already shown
experimentally the possibility to measure the density variation of aerosol and particulate in the atmosphere due
to plumes emitted in forest fires with this kind of systems. The aim of the present work is to demonstrate the
capabilities of our mobile Lidar system, based on a CO2 laser, to detect forest fires and minimizing false alarms.
For this purpose, our system can be operated in both lidar and dial configurations in sequence. The first Lidar
measurement is performed to evaluate the variation of the local density into the atmosphere, using a nonabsorption
water wavelength 10R18 (10.571 μm). If the returned signal reports a backscattering peak, the
presence of a fire is probable. To confirm this hypothesis, a second dial measurement is carried out to reveal a
second component emitted during the combustion process. The chosen second component is water vapour,
which is, as it is well-known, largely produced during the first combustion stage. Measuring the water
concentration peak after the detection of the aerosol density increment (referred to the standard mean
atmospheric value) represents a good method to reduce false alarms with a dial system. In order to test this
methodology, a first set of measurements has been performed in a field near the Engineering Faculty of the
University of Rome "Tor Vergata". A quite small controlled-fire has been lighted into a box at a distance of
about one kilometre from the system. The data acquired at the two wavelengths (10R18 and 10R20) have been
averaged on 100 elastic backscattered Lidar signals. The first results confirm the effectiveness of the
measurement strategy for reducing the number of false alarm preserving the early detection.
This paper presents the goals and some of the results of experiments conducted within the Working Package 10 (Fusion
Experimental Programme) of the HiPER Project. These experiments concern the study of the physics connected to
"Advanced Ignition Schemes", i.e. the Fast Ignition and the Shock Ignition Approaches to Inertial Fusion. Such schemes
are aimed at achieving a higher gain, as compared to the classical approach which is used in NIF, as required for future
reactors, and making fusion possible with smaller facilities.
In particular, a series of experiments related to Fast Ignition were performed at the RAL (UK) and LULI (France)
Laboratories and were addressed to study the propagation of fast electrons (created by a short-pulse ultra-high-intensity
beam) in compressed matter, created either by cylindrical implosions or by compression of planar targets by (planar)
laser-driven shock waves. A more recent experiment was performed at PALS and investigated the laser-plasma coupling
in the 1016 W/cm2 intensity regime of interest for Shock Ignition.
We present the results of an experiment concerning laser-plasma interaction in the regime relevant to shock ignition. The
interaction of high-intensity frequency tripled laser pulse with CH plasma preformed by lower intensity pre-pulse on
fundamental wavelength of the kJ-class iodine laser was investigated in the planar geometry in order to estimate the
coupling of the laser energy to the shock wave or parametric instabilities such as stimulated Raman or Brillouin
scattering, or to the fast electrons. First the complete characterization of the hydrodynamic parameters of preformed
plasma was made using crystal spectrometer to estimate the electron temperature and XUV probe to resolve the electron
density profile close to the critical density region. The other part of the experiment consisted of the shock chronometry,
calorimetry of the back-scattered light and hard X-ray spectrometry to evaluate the coupling to different processes. The
preliminary analysis of the measurements showed rather low energy transfer of the high-intensity pulse to back-scattered
light (< 5%) and no traces of any significant hot electron production were found in the X-ray spectra.
L. Volpe, D. Batani, B. Vauzour, Ph. Nicolai, J. Santos, F. Dorchies, C. Fourment, S. Hulin, C. Regan, F. Perez, S. Baton, M. Koenig, K. Lancaster, M. Galimberti, R. Heathcote, M. Tolley, Ch. Spindloe, P. Koester, L. Labate, L. Gizzi, C. Benedetti, A. Sgattoni, M. Richetta
Generation of high intensity and well collimated multi energetic proton beams from laser-matter
interaction extend the possibility to use protons as a diagnostic to image imploding target in Inertial
Confinement Fusion experiments. An experiment was done at the Rutherford Appleton Laboratory
(Vulcan Laser Petawatt laser) to study fast electron propagation in cylindrically compressed targets,
a subject of interest for fast ignition. This was performed in the framework of the experimental road
map of HiPER (the European High Power laser Energy Research facility Project). In the experiment,
protons accelerated by a ps-laser pulse were used to radiograph a 220 m diameter cylinder (20 m wall,
filled with low density foam), imploded with 200 J of green laser light in 4 symmetrically incident
beams of pulse length 1 ns. Point projection proton backlighting was used to get the compression
history and the stagnation time. Detailed comparison with 2D numerical hydro simulations has
been done using a Monte Carlo code adapted to describe multiple scattering and plasma effects
and with those from hard X-ray radiography. These analysis shows that due to the very large mass
densities reached during implosion processes, protons traveling through the target undergo a very large
number of collisions which deviate protons from their original trajectory reducing proton radiography
resolution. Here we present a simple analytical model to study the proton radiography diagnostic
performance as a function of the main experimental parameters such as proton beam energy and target
areal density. This approach leads to define two different criteria for PR resolution (called "strong"
and "weak" condition) describing different experimental conditions. Finally numerical simulations
using both hydrodynamic and Monte Carlo codes are presented to validate analytical predictions.
In the lidar-dial method, the amount of the water vapor present in the smoke of the vegetable fuel is detected to reduce the number of false alarms. We report the measurements of the smoke backscattering coefficients for the CO2 laser lines 10R20 and 10R18 as determined in an absorption cell for two different vegetable fuels (eucalyptus and conifer). These experimental backscattering coefficients enable us to determine the error to be associated to the water vapor measurements when the traditional first-order approximation is assumed. We find that this first-order approximation is valid for combustion rates as low as 100 g/s.
The PBL is the lower layer of the atmosphere that is sensitive to the effect of the Earths surface, it controls the flow of
heat and momentum between the surface and the free atmosphere, thus playing a key role in atmospheric circulation.
At University of Rome "Tor Vergata", Quantum Electronic and Plasma Laboratories (EQP), two mobile Light Detection
and Ranging (LIDAR) systems have been developed. With these systems the monitoring of the Planetary Boundary
Layer (PBL) has been performed.
The first mobile Lidar system is based on a pulsed Nd:YAG Q-Switched laser source operating at three wavelengths:
1064 nm, 532 nm and 355 nm. Acquiring the elastic backscattered signals, it has been possible to estimate the aerosolitic
backscattering coefficient at the aim to reconstruct the vertical aerosol profiles.
The second one is a Differential Absorption Lidar system (DIAL), composed by a CO2 laser, working in the window
spectral range between 9 and 11μm. With this system it has been estimated the water vapour concentration in the PBL
region using the two wavelengths 10R20 (10.591 μm) and 10R18 (10.571 μm), which represent, respectively, the
absorbing wavelength and non-absorbing one of the water molecule. The comparison of the backscattered radiation at
these wavelengths yields the trace gas number density as a function of distance along the field-of-view of the receiving
telescope.
Diurnal and nocturnal measurements have been performed simultaneity using the two Lidar/Dial systems. Vertical
profiles of the aerosolitic backscattering coefficient and water vapour concentration profiles have been estimated. The
results and their comparison will be present in this work.
Forest fires can be the cause of environmental catastrophe, with the natural outcomes of serious ecological and
economic damages, together with the possibility to endanger human safety. At the aim to reduce this catastrophe
several author have been shown that the Laser light scattering can be uses to reveals the particulate emitted in the
smoke. Infact experimental and theoretical investigations have shown that lidar is a powerful tool to detect the tenuous
smoke plumes produced by forest fires at an early stage. In early 90's Arbolino and Andreucci have shown the
theoretical possibility to detect the particulate emitted in atmosphere from smoke forest fire. Vilar at all have shown
experimentally the possibility to measure the density variation in atmosphere due to plume emitted in forest fire event.
Gaudio at all. have already shown that it is possible to evaluate water vapor emitted in smoke of vegetable fuel using a
CO2 dial system.
In this paper a theoretical model to evaluate the capabilities of a lidar system in fire surveillance of wooded areas will
be presented. In particular we intend propose a technique to minimizing the false alarm in the detection of forest fire by
lidar based on a measurement of second components emitted in a combustion process. Usually to detect a fire alarm a
rapid increase of aerosol amount is measured. If the backscattering signal report a peak, the presences of a forest fire
will be probable. Our idea to confirm this hypothesis is measure the second components emitted in a forest fire at the
aim to minimize the false alarm. The simulated measurements of the humidity amount within the smoke plume will be
carried out by means of Raman analysis. Fixing the burning rate of the vegetable-fuels, the maximum range of
detection will be evaluated.
The quick increase of terrorism and asymmetric war is leading towards new needs involving defense and security.
Nowadays we have to fight several kind of threats and use of chemical weapons against civil or military objectives is one
of the most dangerous.
For this reason it is necessary to find equipment, know-how and information that are useful in order to detect and identify
dangerous molecules as quickly and far away as possible, so to minimize damage.
Lidar/Dial are some of the most powerful optical technologies. Dial technology use two different wavelengths, in order
to measure concentration profile of an investigated molecule. For this reason it is needed a "fingerprint" database which
consists of an exhaustive collection of absorption coefficients data so to identify each molecule avoiding confusion with
interfering ones. Nowadays there is not such a collection of data in scientific and technical literature.
We used an FT-IR spectrometer and a CO2 laser source for absorption spectroscopy measurements using cells filled with
the investigated molecules. The CO2 source is the transmitter of our DIAL facility. In this way we can make a proper
"fingerprint" database necessary to identify dangerous molecules. The CO2 laser has been chosen because it is eye safe
and, mainly, because it covers a spectral band where there is good absorption for this kind of molecules. In this paper IR
spectra of mustard will be presented and compared to other substances which may interfere producing a false alarm.
Methodology, experimental setup and first results are described.
Detection of smoke from forest fire is one of the practical applications of lidar. As it is well known, smoke contains a
large number of small particles of ash or soot, leading to a large backscattering efficiency and consequently favourable
conditions for lidar application.
We have developed a compact mobile lidar system based on Nd:YAG Q-Switched laser source, operating at three
wavelengths: 1064 nm, 532 nm and 355 nm, with emission rate of 10 Hz and pulse duration equal to 5 ns when the laser
operate at the fundamental harmonic and 4 ns for the second and the third ones.
The system has been tested by experimental measurements of the smoke backscattering coefficients carried out in an ad
hoc cell. Since the spatial resolution of laser pulse is smaller than the cell length it has been possible to evaluate the
profile of the smoke backscattering coefficients inside the cell itself. Moreover it has been developed a computational
model for simulating the temporal and spatial evolution of smoke within the cell. These experimental and theoretical data
have been used to optimize the theoretical already developed to study the smoke evolution into the atmosphere.
In this paper measurements of smoke backscattering coefficients into a cell and simulations of smoke evolution will be
presented.
Forest fires can be the cause of serious environmental and economic damages. For this reason a considerable effort has been directed toward the forest protection and fire fighting. In the early forest fire detection, Lidar technique present considerable advantages compared to the passive detection methods based on infrared cameras currently in common use, due its higher sensitivity and ability to accurately locate the fire. The combustion phase of the vegetable matter causes a great amount of water vapour emission, thus the water molecule behaviour will be studied to obtain a fire detection system ready and efficient also before the flame propagation. A first evaluation of increment of the water vapour concentration compared to standard one will be estimated by a numerical simulation. These results will be compared with the experimental measurements carried out into a cell with a CO2 Dial system, burning different kinds of vegetable fuel. Our results and their comparison will be reported in this paper.
Forest fires can be the cause of serious environmental and economic damages. For this reason considerable effort has been directed toward forest protection and fire fighting.
The means traditionally used for early fire detection mainly consist in human observers dispersed over forest regions. A significant improvement in early warning capabilities could be obtained by using automatic detection apparatus.
In order to early detect small forest fires, the use of a dial system will be considered.
A first evaluation of the lowest detectable concentration will be estimated by a numerical simulation. The theoretical model will be used also to get the capacities of a dial system in fire surveillance of wooded areas. Fixing the burning rate for several fuels, the maximum range of detection will be evaluated. The results of these simulations will be reported in the paper.
Two remote sensing techniques used to measure water vapor content in the atmosphere are presented: the Lidar/Dial technique and the GPS data analysis method. The dial method, as is well known, can be used to obtain range resolved measurements or an average concentration measurement on the long path using a target topographic method. This methodology permits measurement of the concentration of atmospheric trace gases and, in particular, water vapour profiles. The second remote sensing method is based on an application of the GPS (Global Positioning System). It enables the assessment of the signal propagation delay from satellites to ground-based receivers. Once ground temperature and atmospheric pressure are measured and the GPS signal delay is known, then an estimate of the columnar water vapour content can be performed. In this paper a comparison between the two remote sensing techniques of water vapour measurement are present.
The DIAL system and the HYPACT model are two useful means to study plume evolution and dispersion. We developed a mobile DIAL system, mounted onto a truck. The DIAL is based on a single TEA CO2 laser source, able to switch between the 'on' and 'off' lines. This set-up allows rapid tuning of the two lines and keeps the misalignment within a range of 0.1 mrad, moderately below the beam divergence. The receiving system is a Newtonian telescope. All the instrumentation and the telescope are located inside the van. A large size scanning mirror, installed on the roof, sends the laser radiation into the atmosphere and, at the same time, it collects the backscattered light. To test all instrumentation, preliminary measurements have been completed to monitor a water vapor plume of a cement factory. The measurements are qualitatively compared against a dispersion plume model run initially from climatological fields.
A dial system based on CO2 laser which can be used routinely having an high degrees of eye safety, has been implemented at the Department of PHysics of University of Calabria. Starting from this, a mobile dial unit has been realized under the project 'LIFE 95/IT/AII/IT/504/CAL' financial support of European Community. We describe the most important feature of the system.
A plasma shutter has been made for cutting nitrogen tail of energy pulse of TEA CO2 laser. Studies to implement all set-ups has been done using preliminarily a TE CO2 laser source. The system is described and the dependence of the gas break down by energy of the discharge is discussed.
Within the framework of our LIDAR activity devoted to air pollution measurements, we realized the injection of a continuous carbon dioxide laser into a high power TE CO2 laser, to get the possibility of better analyze return signal response and to realize a Doppler wind velocimeter. Apart from the need of temporally smooth pulse to examine measurements result, in remote sensing it is desirable to use narrow band laser sources. The request of high spectral performances is manly based on the possibility to use heterodyne detection, on one hand, to improve the signal to noise ratio, and, on the other, to observe and analyze Doppler frequency shift in the return signal. We are engaged into implement a TE CO2 laser source by injection of a cw pulse from a low pressure CO2. Preliminary results we obtained show a smoothing of the output pulse shape and a consequent reduction in spectral band-width, revealing a single longitudinal mode operation.
Recently the application of pulsed laser deposition (PLD) technique to grow different material of relevant interest for applications, especially in the field of micro devices, has been considered. We show that thin films of diamond like carbon (DLC) can be grown by means of the PLD technique, using an XeCl excimer laser. Their characterization was carried out by SEM, Raman spectroscopy and microindenter. We started a study on the etching mechanism of DLC films for possible applications in microsystems technology.
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