The laser is one of the most fantastic and versatile tool invented recently, although its story began with luminescent phenomena, which have been always at the center of curiosity of mankind since ancient times. However the important aspects of the luminescence have been discovered in the past century, and only in the present one the various basic and technical knowledges coalesced for the realization of the first laser device. Since then the field exploded almost exponentially, and thousands of different materials, in the state of solids, liquids, vapors, gases, plasmas, and elementary particles have lased up to now. However only a few of them became practical lasers, which have been used with outstanding results both in basic science, and in industrial and commercial applications. Due to the vastness ofthe laser field, only the most important aspects will be considered here, starting from the essential historical background, describing the rapid evolution of the main laser systems in the past decades, and trying to forecast the near future developments. In general, although a few sectors show signs of maturity, the field as a whole looks well alive and there will be a new golden age as a consequence of impressive technological advances.

Referring to the work carried out in our laboratory, we review low-medium power diode pumped all solid state laser systems for scientific, bio-medical and industrial applications. Side- and end-pumping are discussed and compared for such a laser systems. End-pumped scheme is mainly exploited in this report. Coupling solutions and cavity design are described emphasizing energy deposition and extraction optimization, thermal lens effects, beam quality control and longitudinal mode control. Both cw- and quasi-cw-pumped lasers are considered, operating either in continuous wave, passive Q-switching, and mode-locking regimes. Intracavity and extracavity harmonic generation, optical parametric generation and short pulse generation are among the aims of these all-solid-state sources: some result of these applications are reported.

The use of capacitive Radio-Frequency discharges for the excitation of thin diffusion cooled regions of gas has caused a remarkable breakthrough in the establishment of new CO₂ laser sources. Indeed this technique allows specific power loadings more than one order of magnitude higher than those of conventional slow-flow lasers. At the same time it enables efficient laser operation in sealed or quasi-sealed conditions determining an enormous advantage of these sources over fast-flow ones.Advantages are also determined by the potentiality of pulsing this kind of discharge at high repetition rates, in the range 1-10 kHz. Triggered by these considerations a lot of R and D efforts have been made in this field during the laser decade, giving rise to rugged and extremely compact CO₂ laser sources in the 100-2000 W power segment, useful in medical as well as in low-power industrial applications. To obtain this result several problems had to be faced such as the attainment of a uniform plasma excitation in large area discharges or the extraction of a good quality beam form non-conventional gain region formats. The solutions adopted so far are reviewed, hints on further developments are given.

Hercules is a XeCl excimer laser designed and constructed about ten years ago at the Laboratories of ENEA Frascati. It can deliver up to 10 J output energy at a repetition rate of 10Hz. Since 1992, Hercules is a laser facility available to check the feasibility of processes and/or the effects occurring to materials irradiated with ultraviolet radiation at very high energy fluence or at high intensity level or over a large area. Here we present a summary of the main mechanical, electrical and optical characteristics of Hercules, together with a selected list of irradiation experiments, including the generation of soft x-rays amorphous silicon.

The free-electron has proven to be an invaluable source of radiation in the IR spectral range. Its main qualities are its spectral range, its tuning range and tuning speeds, its high peak power and its the short pulse lengths. In the last decade, several FELs have been designed and built as user dedicated facilities. Presently, 7 IR FELs are running more than 1000 hours/year for users, who are working in various scientific fields.

Recoil-induced resonances have been observed in pump-probe spectroscopy with cold atoms. On the other hand, a model for collective atomic recoil laser has been developed by R. Bonifacio and co-workers. These two systems rely on the recoil effect due to the absorption or the emission of a photon by an atom and share may features. In this paper, we shall investigate the relationship between the two models and clarify the underlying physics. We'll review also the experimental results.

Because of the present success of the Erbium doped fibre amplifiers in telecommunication systems, there is now a trend to look for more compact amplifiers, also based on rare earth doped hosts in wave guide structures, but in the much more compact geometry of short planar wave guides. The shortening of the active length shall be obtain only if one of the following conditions are fuffihled: the active ion concentration-cross-sections product can be increased by three order of magrntude. From basic principle, it is shown that because of the rather weak interaction with the surrounthng, the ion crosssections does not vary a lot when changing the glass host arid that the ion-ion interactions shall fundamentally limit the active ion concentration. Tentative solutions to this problem are presented.

Synthetic diamond, deposited by Chemical Vapour Deposition (CVD), is becoming an interesting alternative for ZnSe as a window material for high power CO lasers. Although the infrared absorption of CVD-dianiond is higher than of ZnSe, this drawback is largely overruled by its better thermal conductivity, leading to smaller temperature gradients in the window and hence a less distorted laser beam. Electronic Speckle Pattern Interferometry (ESPI) is applied to study the on-line deformation of ZnSe and CVD-diamond anti-reflective coated output coupler windows exposed to a high power CO laser beam. It is seen that a ZnSe window already starts deforming at moderate beam power (100 W), while a diamond window does not deform considerably up to a beam power of 700 W.

A convenient cw laser source is demonstrated covering the spectral range 1.6 -1.9 run. The light source is based on the cascaded Raman generation in a standard optical fiber with moderate germarnuin concentration. The new Raman laser can be used as a light source ofpuniping for this particular spectral region.

Light amplification resulting from XeCl multiphoton dissociation of mercury-bromide was observed in the blue- green region between 502 and 505 nm. We report the formation of electronically excited HgBr radicals and measured the gain of the medium.

The resistance and inductance of a laser discharge in a pulsed gas laser are considered theoretically in this paper. The total charge and the dimensions of the discharge volume are responsible for the resistance and inductance of the laser channel respectively. Generally, the inductance increases either decreasing electrode length or discharge thickness, or increasing the interelectrode distance. The direct dependence of the resistance and inductance with the microscopically plasma parameters, total charge and drift velocity, was discovered in this paper through the external driving circuit and especially through its capacitance. The values of the capacitors form the total charge while the coupling of the capacitors in the circuits forms the drift velocity. These are inferred dealing with the two most common circuits used in a pulsed gas laser, namely the doubling circuit and the charge transfer circuit for all possible combinations of capacitance allocation.

The uniformity and stability of discharge process in a high pulse repetition frequency long pulse XeCl laser are investigated for three different copper electrode roughnesses in single shot regime and versus PRF. The discharge quality evolution is experimentally analyzed from discharge photographs obtained with CCD video camera and pressure perturbation measurements achieved with a piezoelectric pressure probe placed very close to the discharge volume.

Low energy electron beam irradiation of LiF single crystals and polycrystalline films induces efficient formation of stable laser active defects emitting in the visible spectral range at room temperature, together with a consistent increase of the real part of the refractive index in the same wavelength interval. The use of electron lithography techniques look promising for the realization of active channel waveguides.

Long-wavelength vertical-cavity surface-emitting semiconductor lasers are investigated and heating effects on the light vs. current characteristics of VCSELs are analyzed by thermal-electric, optical, and electronic modeling. The model includes nonuniform current injection, carrier diffusion, stimulated emission, distributed heat sources, and active material band structure calculations. Device parameters such as threshold current, and external quantum efficiency are evaluated. Simulated power vs. current characteristics exhibit the typical thermal roll-over in continuous wave operation. The model is applied to two specific optimized underetched structure designs in order to provide an understanding of the current-funneling mechanism and the thermal limitations of such devices.

In this paper, a detailed analysis of the transient heat flow in a VCSEL is carried out. The transient thermal response of VCSEL axisymmetric structures is calculated based on a Green's functions method to solve the time- dependent thermal conduction equation. Based on this approach, the heat flow inside the device due to the dominant heat sources in the active and passive layers has been assessed. The influence of the current spreading and the material parameters on the transient thermal response is investigated, and the temporal evolution of the temperature distribution and the lasing wavelength shift are calculated and found to be in good agreement with results obtained by a finite element method. Finally, the time constant of the active layer temperature rise due to a stepwise increase in current for a double-fused long wavelength VCSEL is calculated.

Great hopes currently lie in new all-optical switching devices based on polymer film waveguides. Here, the design of a novel all-optical waveguide frequency converter is reported, the research activity for which was carried out within the framework of the Italian Project on Telecommunications.

A fiber optic delay line was designed and developed to be used in a microwave signal processing system. The device was based on a 10km 9/125 microns single mode fiber delay line. A single mode 1550nm/1mW laser diode was used as a transmitter modulated up to 500MHz. A PIN photodiode with incorporated transimpedance amplifier was used to convert the optical signal back to the electrical. The paper presents full technical details and optical performance characteristics of a low cost easy to use fiber optic delay line.

A useful tool in working with non-visible optical radiation is a monitor/indicator with an alarm, activated when the irradiance exceeds a preset value. In extending this tool to more applications, this paper describes the design and development of a small active lightweight indicator in two versions, for detecting, observing and responding to almost every preset level of the optical radiation, extended from low up to high optical power densities. The monitor/indicator, in the form of a small cylinder or a pencil or a thick card, with low power consumption and linear response, may be used as active warning element on the side of goggles, spectacles, helmets etc., or as an active element for replacing the laser indication passive cards. The indicator's audible and visible output alarms are like the indication output of the ionizing radiation monitors. The alarm is activated if the irradiance exceeds a preset limit, which may be set equal to maximum permissible exposure. The main parts in both versions are a photodetector and a FET-input operational amplifier, in an optoelectronic integrator and an intensity/frequency converter. This circuit reacts with sufficient accuracy in CW or pulsed radiation down to the optical irradiance.

Band engineering conception of asymmetric quantum-well (QW) heterostructures widens possibilities to control functional performances of semiconductors lasers and other semiconductor optoelectronic devices. We have analyzed a new type of laser diodes and amplitudes based on asymmetric multiple-QW heterostructures having active layers of different thicknesses and component compositions. For such QW systems, it is possible to change the optical gain spectrum in a wide range and to control the set of definite amplification frequencies due to selecting the width, component composition, and doping of QW and barrier regions.

The rate of spontaneous radiative recombination and gain coefficient for the high-doping superlattices versus the pump current are calculated in the model with no k-selection rule. Results for the inversion current density and differential gain at suitable design of superlattice parameters are presented.

Coherent detection, as a process for demodulation of an optical signal, is used to a great extent in modern optical communications. In some configurations of this technique, the information which exists in the frequency or the phase of the optical signal can be derived by using the same beam as a carrier and as a local-oscillator signal too. In this communication, we present a theoretical analysis of such a self-homodyne system, which is composed of a laser source, an electrooptic modulator, a photodetector and all the necessary optical components. The whole analysis is accompanied with a PC-supported program, which offers the possibility to study the system for various kinds of optical polarization but with the same incident optical power on the photodetector, independently of the various optical components.Furthermore, this program provides the possibility of changing the respective values at will, after we have introduce direct and alternating voltage as a signal. Finally, the study of the various harmonics of the output signal's spectrum gives the possibility to discover the advantages that the circular polarization offers compared with other kinds of polarization.

We demonstrate the applicability of a genetic algorithm (GA) to control the focus of an adaptive optical system using a liquid crystal spatial light modulator. The optical setup and the algorithm applied are set to fitness type reinforcement for learning. The particular GA developed optimizes the phase shifts in 32 independent pixels, and is biased towards approximating continuous functions that suit the focusing problem. The learning process is demonstrated to work reliably even in the presence of experimental noise.

A new concept for generating zero order Bessel beams was studied. A point source illuminated a Fabry-Perot etalon, which produced a concentric interference ring system in front of an imaging lens.If the lens aperture was adjusted so that it transmitted the first ring only and blocked all others, a zero order Bessel bean was generated beyond the lens. The spatial intensity distribution beyond the lens was calculated numerically using a wave optical model. The calculated and measured axial intensity distributions were compared. An approximate analytical expression was derived to describe the radial intensity distribution in planes perpendicular to the optical axis.

The demands on the quality of laser beams are becoming much greater. Traditional methods of measuring laser intensity profile such as burn spots, mode burns, and viewing the reflected beam, are woefully inadequate for today's applications. The increasingly high quality of lasers is to a large extent due to the availability of electronic beam profile instruments. These instruments provide a real time view of the laser beam profile that provides greater intuition to enable laser optimization. Also, electronic laser beam profilers produce much more accurate quantification of laser beam properties. The accuracy of these measurements enables scientists to fine tune the laser properties to a greater extent than previously possible.

A novel definition of the times-diffraction-limit (TDL) number of a laser beam is given. A comparison is made with the commonly used beam-propagation parameter M², which is unreliable for hard-edge beams, like those produced by unstable resonators with diffraction output coupling. The new suggested TDL number definition doesn't rely on the real beam comparison to a Gaussian beam, but on the comparison of the far-field performances of the real beam with respect to those of a uniphase beam with the same amplitude profile in the near field. A practical method is also given for the estimation of the TDL number of real beams. Finally, this procedure is applied to the high-peak-power laser beams generated by two excimer laser systems developed in ENEA.

The evolution of the main parameters of the intracavity laser radiation oscillating in a Gaussian-cavity applied to a XeCl laser, has been experimentally investigated. It has been found that the temporal evolution of the main laser beam parameter was well approximated by the evolution of a Shell-Gaussian model beam propagating in a bare Gaussian cavity, even if the intensity profiles of the oscillating radiation were quite affected by XeCl laser gain characteristics.

We present a measurement of the time-behavior of the divergence of pulsed laser beams, joining the time- resolution capability of photodetectors and the space- resolved information of the knife-edge technique. This method has been tested by using HERCULES, a high output energy XeCl laser facility, equipped with two different unstable resonators. The time-resolved beam divergence was much higher than the time-integrated one at the leading edge of the laser pulse duration, and it had a minimum before the peak of the laser pulse. The consequences on the optimization of laser-matter interaction processes are discussed.

Experimental studies of the spatial power distribution in the radiation beam from the industrial, transverse - flow cw CO₂ laser working in the range up to 1.5 kW are reported. A beam diagnostic system utilizing a rotating pinhole scanner was developed and used to record and measure the spatial distribution of the power density in the laser processing region. The beam dimensions for locations at various distances to the focal plane were derived from the recorded profiles analysis agreed with those obtained by the knife-edge technique implemented in previous experiments.

The evolution operator formalism, combined with appropriate decomposition techniques of exponential operators, has revealed an effective strategy to treat evolution-like problems in both classical and quantum context. The continuous original equation is turned into a set of finite- difference equations, which preserve at a discrete level the basic features of the corresponding continuous model. The resulting scheme is easy to be encoded and demands for less computer time. The method can be applied to the paraxial gaussian optics, described by the 1D parabolic wave equation. Within this context, the formalism generates an explicit difference scheme, which provides a flexible numerical integration procedure, accounting for higher-order aberrations as well.

Some ultrafast phenomena occurring in an active microcavity have been investigated. This device can behave as an efficient source of non-classical light, when a small number of molecules inside are excited by a femtosecond laser.In this way single photon n > states are generated with anon-classical sub-Poissonian distribution. Multiple excitations of a larger number of molecules can give rise to collective phenomena because of the strong super-radiant ultrafast coupling within the transverse region of the microcavity electromagnetic field. This process has been experimentally studied by means of a high efficiency, single photon, femtosecond non-linear optical gate.

This paper presents an experimental technique for measurement of the contrast ratio of ultrashort UV pulses. The multiple shot device based on the scheme of difference frequency generation is, to our knowledge, the only cross correlator in the UV so far, which offers a dynamic range of >= 10⁷ and operates with input pulse energies as low as 5 (mu) J. Changing the cross correlator into single shot mode, the temporal shape of the UV pulse can be measured.

The nonlinear optical response of fullerene solutions is examined as a function of the incident radiation pulse duration and intensity. Using the z-scan technique, the nonlinear absorption and the nonlinear refraction are studied for 10 nsec, 532 nm and 0.5 psec, 497 nm laser pulses. The corresponding nonlinear parameters are determined and their intensity dependence is shown to be the indicative parameter for the understanding of the origin of the observed nonlinearity. Possible applications of the nonlinear optical properties of fullerenes in optoelectronics are proposed.

The stimulated Raman scattering (SRS) technique has been sued for upward and downward shifting the 3rd harmonic of a pulsed Nd:YAG laser into the 274-503 nm wavelength region. The gases investigated were hydrogen (H₂) and deuterium (D₂), using helium (He) as buffer gas. Experimental results on the output Stokes and anti-Stokes conversion efficiencies of the forward SRS technique in H₂, D₂ and He, versus Raman gas pressure and input pump energy, are presented. Conversion efficiencies more than 40 percent were achieved and the output energies obtained at the various ultraviolet and visible wavelengths were of the order of several mJ.

For the first time stimulated Raman scattering (SRS) in multimode silica fibers pumped with long XeCl laser pulses has been observed. The spectral and temporal development of SRS both experimentally and theoretically have been studied. Two orders of SRS have been obtained in the 311 divided by 317 nm spectral region. The experimental result are in good agreement with computer simulations of SRS in which effects of self- and cross-phase modulation and group velocity dispersion are negligible. In the numerical model are included experimentally measured spectra of the Raman gain curve and the pump laser spectra.

Simulated Raman scattering in H₂ has been investigated with circularly, linearly, and randomly polarized XeCl laser pulses by varying H₂ pressure. The effects of pump radiation polarization and focusing geometry on Raman conversion to rotational and vibrational lines have been investigated. It is shown that circularly polarized pump pulses, high-angle focusing geometries, and/or Raman medium pressures favor the conversion to purely rotational lines, as a consequence of gain suppression effects on vibrational scattering.

The 90 femtosecond laser induced fragmentation at 375 nm for a number of different nitro-molecules is compared to that induced by a nanosecond laser at the same wavelength by means of time-of-flight mass spectrometry. The potential of femtosecond laser mass spectrometry for analytical purposes is discussed.

We have studied analytically the theoretical behavior of a Fabry-Perot cavity using a birefringent non-linear material in a polarizer-sample-analyzer system. The working parameter of our device is the direction of polarization of the incident light. Principal results are presented.

We discuss the ability and effectiveness of electronic spectroscopy to reveal rotational isomerism by presenting some examples of the S₁ implied by S₀ electronic spectra of non-rigid molecules. One or two photon electronic spectra have multiple features when the molecule has more than one conformational preference. Torsional bands showing up in the spectrum complicate the assignment of conformers. Hole burning experiments give definite conclusions on the existence of rotational isomerism and an example from the literature is given.

A DFB semiconductor diode laser spectrometer operating between 1 micrometers and 2 micrometers has been developed. High sensitivity detection measurements are carried on with different schemes, from pure linear absorption to two-tone frequency modulation. Results, including collisional lineshape parameters, are reported for various molecules of medical and environmental interest such as CO, CO₂, H₂S, NH₃ and O₂.

The fluorescence spectrum of rhodamine 6G incorporated in thin surfactant films demonstrates an extensive narrowing of the spectral width at relatively low excitation light fluence due to coherent scattering caused by molecular aggregates present in the film.

Experimental results are presented concerning the application of laser-induced breakdown spectroscopy (LIBS) for the detection of metals in plastics and biological tissues. LIBS has been used for the detection and the determination of the concentration of antimony in plastic and manganese in human hairs respectively. Calibration curves are presented for the above metals and the limiting factors of the technique are discussed.

A refined diode laser based resonance ionization mass spectrometer for highly selective ultratrace analysis is presented, which combines coherent narrow-band multistep resonance excitation and ionization with a compact quadruple mass spectrometer. The widespread analytical potential and applicability of this system is demonstrated in the determination of calcium trace and ultratrace isotopes for cosmochemical studies, medical investigations and radiodating. For a detailed theoretical understanding of the coherent high resolution multistep excitation process a description in the density matrix formalism was worked out. For calcium optical isotopic selectivities of more than 10¹⁰ and efficiencies of up to 5 percent are predicted, which compare well to the analytical requirements for ⁴¹Ca-determination, which reach a maximum isotopic selectivity of more than 10¹⁵. Experimentally different ionization schemes, including single-, double- and triple- resonance excitation of calcium, have been investigated. The first-step excitation at 422,7 nm requires frequency doubling of a diode laser, while second and third steps are directly excited with extended cavity diode lasers. Analytical measurements cover meteorite and blood samples and demonstrate the feasibility of the predicted specifications. Continuing work will focus towards the application of the full triple-resonance scheme for ultra low-level measurements of ⁴¹Ca and shall establish resonance ionization mass spectrometry as a competitive technology to accelerator mass spectrometry.

Among the numerous detection methods applicable in spectroscopic gas detection systems photoacoustics is probably the simplest, most cost effective, yet a highly sensitive one. By using a properly designed photoacoustic cell, equipped with a commercial microphone and electronics for phase sensitive detection, absorbed electromagnetic radiation as low as 10 nW can be easily detected. The choice of a suitable light source for PA gas detection, however, is crucial in order to preserve the simplicity and practical advantages of the combined gas detection system. In the photoacoustic system presented here, therefore, external cavity diode lasers have been adopted. Contrary to ordinary diode lasers, external cavity diode lasers are ideal sources for spectroscopic studies as they have a narrow linewidth and ar continuously tunable in a relative wide wavelength range. External cavity diode lasers operating in different wavelength range have been developed and concentration determination of water vapor gaseous mixtures are presented. Sensitivity of the system presented here could reach the ppb. level under optimal conditions.

The laser induced fluorescence (LIF) spectrum of LiCaAlF:Nd³⁺ (LiCAF:Nd) single crystal, pumped by an F₂ pulsed discharge molecular laser at 157.6 nm, was obtained in the vacuum ultraviolet (VUV) region of the spectrum. The fluorescence peaks were assigned to the 4f²5dyields4f³ dipole allowed transitions of the Nd³⁺ ion. The LIF spectrum of the crystals, indicates that the 4f³yields4f²5d dipole transitions, originate from the low Stark components of the ⁴K_11/2 level of 4f²5d configuration. The absorption spectrum of the crystal samples in the VUV was obtained as well. The electric crystal field splits all the levels of 4f²5d mixed configuration. We observed seven dipole transitions, between the ⁴I_9/2 ground level of 4f³ configuration and the Stark components of the levels of 4f²5d configuration of the Nd³⁺ ion.

Vacuum ultraviolet fluorescence emissions of alkali rare gas triatomic ionic excimers have been observed. These molecules have been produced by electron beam excitation of rare gas alkali mixtures at high pressure and high temperature. Spectroscopic and kinetic studies have been performed on Kr₂⁺Cs ions which exhibit a spectrum centered at 159nm. Binding energy of the lowest excited state has been estimated. Simple kinetic considerations allowed us to propose two formation processes of these ions and to estimate their rate constant.

We present a theoretical analysis of temporal autocorrelation functions of multiply scattered light in turbid dynamically heterogenous random media. Particular geometries of planar slab and cylindrical capillary inserted in an otherwise macroscopically homogeneous medium are considered. Analytical expressions for time autocorrelation functions of depolarized scattered electric field measured at the sample surface are derived assuming that scatterers dynamics inside dynamically heterogeneous region differs from that in surrounding medium. We show that space resolved measurements of the temporal autocorrelation function of multiply scattered light at the sample surface provide information on spatially heterogeneous particle dynamics inside the sample and allows one to image hidden dynamic inclusion under conditions of no static scattering contrast. Spatial contrast in this case is purely dynamic and can be provided by different particle sizes as well as by different types of particle dynamics inside the inclusion and in background medium. The limitations of presented theoretical approach are outlined. Finally, we estimate the performance of the imaging technique based on the considered theory.

A series of field experiments for laser triggered lightning have been carried out targeting the winter thunderstorms in Fukui, Japan. A combination of a 2 kJ CO₂ laser system, a 600 J Nd-glass laser and a 4th harmonics 100 mJ YAG laser was used to produce a plasma channel which are effective to trigger and guide an electrical leader from the lightning tower. A new scheme of autotriggering laser system by preliminary breakdown (PB) has been developed. The PB triggering system demonstrated its capability of irradiating the laser at the right timing for triggering the leader. On February 11th 1997, in the field experiment, the electric leader was initiated by the laser plasma using the PB triggering system for the first time. A number of diagnostics including UHF interferometers, a tower current monitor, a capacitive antennas verified the initiation of leader triggered by the laser plasma both in time and space.

This paper describes the needs for establishing a mobile laser laboratory (LIDAR) for air pollution monitoring in the Athens area. It also gives the specifications of the laser unit of the LIDAR system and the various studies to be performed in Athens area.

The increasing need for the recording and monitoring of the marine pollution, as well as the disadvantages usually presented by the conventional methods to qualitatively and quantitatively determine the pollutants in the marine environment, have led to the development of a new method, which is based on the technique of laser induced fluorescence combined with the use of optical fibers. In this work, we present the basic principle of the method and its improvement referred to the appropriate selection of the wavelength excitation: this permits the qualitative determination of gasoline and jet-oil in water. Furthermore, based on the different life-times, we applied the method of time-resolved spectroscopy and succeeded in identifying anthracene and pyrene, in a mixture of both aromatic compounds, despite their spectral overlap and the weak fluorescence of pyrene.

Hydroxyl gas-phase reactions play a very important role in air pollution. For the majority of chemical compounds of the atmosphere, the reaction with OH radical s is an intermediate one, part of a long chain reaction. A laser photolysis-laser induced fluorescence technique has been sued to study OH reaction kinetics with dioxane. The apparatus consists of two synchronized pulsed laser systems, a six cross flow/steady gas reactor, a photomultiplier for LIF detection and control electronics. The first laser is used for the production of OH radicals by photolysis. The second laser provides a probe-beam which excites the OH radical electronically. Then, the relative population of OH radicals is monitored time-resolved by laser induced fluorescence. All experiments are performed under pseudo- first order kinetic conditions. The major advantages of this technique are: (1) Capability to measure OH reaction kinetics over an extended temperature range, with different reactants using the same apparatus. (2) Generation of a clean source of OH radicals. (3) Capability of atmospheric pressure measurements. (4) Micro-scale simulation of atmospheric reactions.

The point to point telecommunication in the atmosphere with laser signals using the existing optoelectronic technology is an option of the modern communications design. An optical link is strong depending on the optoelectronic hardware parameters and to the topology or to the environment of the applications area. Many laser-links are already fabricated for use in military or in commercial applications. Main advantages are the freedom from licenses, the RFI-EMI immunity, the wide bandwidth and the information security. Main disadvantages are the atmospheric steady and variable attenuation, the radiation hazards and in some cases the material cost. Based on this know-how we describe in this paper the more important broadcasting parameters of radio- TV-teletext programs with laser beams, starting from the atmospheric transmission influence, continuing with a laser selection guide and with some broadcasting electronic techniques and ending with the proposed modification of a coherent laser-link to a new active receiver system which fulfill normal or special laser broadcasting options. Possible applications of our study may be the point to multi-point optical communications for local pay TV, the allocation of optical bands for broadcasting, the radii of cellular laser broadcasting, the simulcasting with laser and RF carriers, the implementations of an interactive Radio and TV, etc.

Laser techniques for local particle velocity and size measurements in flows are presented and discussed. The laser doppler anemometer utilizing the Doppler shift of light scattered on small particles in a flow for velocity measurements is the basis of the presented techniques. Furthermore phase Doppler anemometry based on the spatial properties of the Doppler shift and shadow Doppler velocimetry utilizing the shadow image of particle for size measurements are briefly discussed. Experimental results illustrating the use of the techniques are presented. These comprise particle velocity measurements in a sudden expansion liquid solid flow as well as in a model of a beater wheel mill. PDA measurements of the size distribution of droplets produced by a nebulizer ar also presented.

The unsteady velocity fields downstream of a cylinder and of a double-circular arc blade under an angle of attack were studied by applying the particle image velocimetry (PIV) technique. The experiments were conducted in a small free- surface water tunnel in the laboratory of hydraulic machines of the National Technical University of Athens. The statistical mean displacements of particles suspended into the fluid, corresponding to two different frames a certain time interval apart, were computed by employing the cross- correlation technique. The result of this analysis was the computation of about 1000 velocity vectors for each pair of frames. Based on this information, it was possible to detect and quantify the interesting flow phenomenon of vortex shedding, like the motion of coherent vortical structures shed into the flow, compute their circulation and vorticity as a function of space and time as well as calculate the forces exerted upon the bodies by the fluid.

Several aspects of the applications of laser technology in cleaning and diagnostics of painted artworks are reviewed. Laser and material parameter studies leading to the optimization of the cleaning process are presented while the use of spectroscopic techniques for obtaining information on the mechanism of the ablation process and probe possible photochemical effects is discussed. Furthermore, holographic interferometric techniques for detecting possible mechanical stress induced by the laser during the cleaning process are employed and preliminary result are shown. Finally, examples of the applications of imaging techniques in artwork diagnostics are presented.

We use optical methods for in-situ diagnostics in pulsed laser deposition of high temperature superconductive thin films. Our interest is focused on the composition modifications experienced by the plume of ablated material during its expansion from the target to the substrate in a molecular oxygen environment, which constitute a key point for the attainment of the correct film stoichiometry. Our diagnostics, based on absorption spectroscopy of atomic oxygen, provide a reliable tool for accurate analysis of the molecular oxygen dissociation involved in the reactive- collisional processes.

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.

Nickel coated mild steel specimens were irradiate with a high power excimer laser. Laser induced surface structures were observed by means of microscopy. The appearance of nickel oxides on the specimens surface was observed on x- rays diffraction spectra. The surface roughness was noted to be dependent on the lasing conditions. Energy dispersive x- rays analysis showed that iron atoms diffused into the nickel coating and nickel atoms diffused into the steel substrate.

Micron-sized deposition and etching of W in WF₆ + H₂ atmosphere is investigated by local laser-induced heating of thin tungsten layers on quartz substrates. The process is strongly dependent on the partial pressures of the two gases. A process with high amount of hydrogen permits deposition of W, whereas etching of W occurs if the working gas does not contain hydrogen.

Pulsed laser deposition technique (PLD) has been successfully used to grow artificially layered films of the CuBa₂(Ca_1-xSr_x)_n-1 Cu_nO_y compound using only two targets having nominal composition BaCuO_y and (Ca_1-xSr_x)CuO_y respectively. n was varied between 2 and 5. The kinematic analysis of the x-ray diffraction spectra reveals that the average random discrete thickness fluctuations which affects both the BaCuOy and (Ca_1-xSr_x)CuO_y layers are much smaller than one atomic layer. Such features are confirmed by the appearance of sharp peaks even for the nequals2 artificially layered structure where only one (Ca_1-xSr_x)CuO_y cell is deposited in the stacking sequence. A major difference is found in the behavior of resistivity between films containing Sr and Ca respectively. Namely (BaCuO₂)₂/[(Ca_1-xSr_x)CuO_y]_n films never show any trace of superconductivity, while [BaCuO₂]_n/[CaCuO₂]_n films result to have, for growth oxygen pressures P > 0.2 mbar a full transition by laser deposition technique with a low interfacial disorder and give strong support to the idea of synthesizing new artificial high Tc structures by the PLD technique.

Zinc specimens were irradiated with a high power excimer laser. Under specific lasing conditions, zinc oxide was detected on the x-rays diffraction spectra. The surface roughness of laser treated specimens was found to be depended upon the lasing conditions. The surface layers of laser treated zinc specimens presented higher microhardness as compared to the untreated zinc specimens.

Industrial manufacturers produce many types of pressure gauges and transducers according to the applications, for gas or liquid, for high-medium and low pressure ranges. Nowadays the current production technology generally prefers to weld by micro TIG source the metallic corrugated membranes to the gauge or transducer bodies for the products, operating on the low pressure or medium pressure ranges. For the other ones, operating to high pressure range, generally the two components of the transducers are both threaded only and threaded and then circularly welded by micro TIG for the other higher range, till to 1000 bar. In this work the products, operating on the approximately equals 30 divided by 200 bar, are considered. These, when assembled on industrial plants, as an outcome of a non-correct operating sequence, give a 'shifted' electrical signal. This is due to a shift of the 'zero electrical signal' that unbalances the electrical bridge - thin layer sensor - that is the sensitive part of the product. Moreover, for the same problem, often some mechanical settlings of the transducer happen during the first pressure semi-components, with an increasing of the product manufacturing costs. In light of all this, the above referred, in this work the whole transducer has been re-designed according to the specific laser welding technology requirements. On the new product no threaded parts exist but only a circular laser welding with a full penetration depth about 2.5 divided by 3 mm high. Three different alloys have been tested according to the applications and the mechanical properties requested to the transducer. By using a 1.5 KW CO₂ laser system many different working parameters have been evaluated for correlating laser parameters to the penetration depths, crown wides, interaction laser-materia times, mechanical and metallurgical properties. Moreover during the laser welding process the measurements of the maximum temperature, reached by the transducer top, has been read and recorded. At least some transducers, before the usual destructive testings, have been undertaken to many pressure test cycles to verify any pressure drops, the transducer sealing and the total quality of the new product.

Even if many steels and alloys have been welded on the last years, nowadays there are some other stainless steel alloys that need a further comprehension when they have to be welded. Typically these alloys are martensitic and precipitation hardening ones that still present some problems to be weld, i.e. hot cracks, fragile beads, an excessive grain size and other surface defects. In this work some martensitic stainless steels of which a AISI 420B, a AISI 440C and a AISI 630 have been studied. The last one is always with a martensitic structure but, in particular, some interesting mechanical properties are reached by a precipitation hardening process. This research has experimented and studied the mechanical and technological properties of the welds obtained on the above cited AISI 420B, AISI 440C and AISI 630, welded by 1.5 kW CO₂ laser. The results have also been compared with the ones obtained on ferritic stainless steels AISI 430 and 430F. A technological characterization of the welds has followed as metallographic tests and evaluations, microhardness, tensile and fatigue tests.

It has been demonstrated that the laser irradiation of the specially synthesized polymer Poly(bis-alkylthio-acetylene)- PATAC induces the generation of highly permanently conducting sites in the material which remains an insulator in the unexposed areas. Conductivity changes by 16 orders of magnitude have been observed. The conductivity values of the final reaction products are in the level of a heavily doped semiconductor. These conductivity values make the PATAC coated materials suitable for microelectronic applications such as the laser direct imaging of conducting paths and circuit structures.

3D-structures obtained by means of laser cladding of the metal alloy powders: bronze B10 and stellite 6 and the process parameters are studied experimentally. The structures are made trace-on-trace by remelting of the metal powder injected into the focusing region of the 1.2 kW CO₂ laser beam. For the powder and sample feeding rates of 8-22 g/min and 0.4-1.2 m/min, respectively, and the applied beam intensities not exceeding 2 X 10⁵ W cm^-2 the process is stable and regular traces connected via fusion zones are produced for each material. The thickness of these zones does not exceed several per cent of the layer height. The process results in the efficient formation of multilayer structures. From their geometry the effect of energy coupling and interaction parameters are deduced. Moreover, the microanalysis by means of SEM- and optical photographs of samples produced under different experimental conditions confirms the expected mechanical properties, low porosity and highly homogenous structure of the multilayers. In addition to the known material stellite 6 the bronze B10 is originally proposed for a rapid prototyping.

In this work the electron beam current and beam emittance measured for an Al and a diamond film cathode irradiated with two different UV excimer lasers, XeCl and KrCl, are presented. The output current was measured with a fast Rogowski coil while the emittance was determined with a new diagnostic setup composed by two movable slit arrays and an array of small cups. The phase space area occupied by the electrons at the output was determined by the current measured with the cups and by the position of the slits. With a 4 mm² beam spot the maximum current from an Al cathode was 740 mA and from a diamond cathode was 560 mA with the KrCl laser. The corresponding emittance values were 130 and 50 for the Al and the diamond cathode, respectively. From these values the normalized beam brightness were estimated to be 0.18 X 10⁹ A((pi) m rad)^-2 for Al cathode and 0.92 X 10⁹ A((pi) mrad)^-2 for diamond cathode.

A coherent laser sensor, able to achieve measurement of absolute and relative distance of real targets, has been developed for advanced robotic applications. A brief theoretical description of the expected behavior of such system is reported for static and dynamic targets; the theoretical range error dependence from the signal to noise ratio is also described. Experimental results for measurements of static and vibrating real targets are discussed.

In robot arc welding applications, in order to overcome inaccuracies of the robot itself and the workpiece, the tracking of the seam is of primal importance. To detect the seam, a novel sensor based on a laser scanner and using triangulation methods has been developed. A definite problem of the development is the difference in the optical power emitted by the arc which is in the range of hundreds of Watts and the power of the diode laser in the range of mW. In order to achieve good signal to noise ratio, it is necessary to select a wavelength where the glow of the arc is minimal and design an appropriate interference filter. For this purpose detailed measurements and analysis of the spectrum of the welding arc have been performed. The measurements extend for the UV region of the spectrum to the near IR region. The study was concentrated on the welding of ferrous metals using as shielding gas a mixture of 80 percent Ar and 20 percent CO₂ and welding currents in the range of 100A to 160A. The measurements have revealed the presence of many strong emission lines in the spectrum.

Lasers have many industrial applications, ranging from very high precision mechanics, to industrial marking for functional and/or decorative purposes. In this paper the author, on previous specific experience deals with the extension of the equipment capability. The goal is reached with an easy marking process modification and a high performance software development.

The morphological and compositional changes which take place during the laser irradiation of YBCO targets are discussed. The understanding of the evolution of target composition, will lead to better control of film quality. In the case stated here, a XeCl excimer laser was used to irradiate rotated and also non-rotated YBa₂Cu₃O_7-x targets. The modified surface of these targets was systematically studied by scanning electron microscopy and energy dispersive x-ray microanalysis. It was observed that some crucial deposition parameters, such as the number of pulses and fluence has a strong effect on the roughening of the target. A comparative study was done on the derived High-Tc superconducting thin films. It was shown that the conditions during the preablation procedure which affect the target surface morphology correlate closely with the appearance of laser droplets on the film surface.

We report a YBa₂Cu₃O₇ PLD method designed to reduce the oxygen deficiency in the as deposited YBCO superconducting thin films.OPtical dissociation of O₂ buffer gas in front of the plume using a second IR laser pulse simultaneously with the UV laser beam producing the ablation plasma is proposed as a method for oxidation enhancement and oxygen enrichment in the deposited film. Oxides enhancement measurements were performed by optical spectroscopy on YO, BaO and CuO lines at large distances from the target surface. Temporal evolution of ionic, neutral and oxide lines was analyzed in 400-620 nm region, in correlation with plasma expansion in the ambient gas.

Pulsed laser ablation is well established as a universal tool for surface processing of organic polymer materials. The polymer ablation efficiency of different laser wavelengths, from 355 nm to 532 nm, is studied for short laser pulses, of nanosecond pulse duration. Ablation rates of polymers have been measured by irradiating the polymers using a pulsed Nd:YAG laser. This laser source produced pulses at the second and third harmonic simultaneously at (lambda) equals 532 nm and (lambda) equals 355 nm. Effective ablation was also observed by irradiating the polymer samples with the Raman-shifted Nd:YAG laser, at (lambda) equals 397.1 nm, in order to investigate comparatively the ablation efficiency at different laser settings. For transparent materials, in the corresponding ablation wavelengths and pulse width, the dependence of the ablation rate on the laser spot diameter and the laser energy fluence has been investigated. In general, the polymers used in this work show a more or less pronounced increase of the ablation rate with decreasing spot diameter for the same fluence, especially in the case of visible laser irradiation.

The development of conical structures on the surface of excimer laser ablated polymers, is studied. It is demonstrated that this phenomenon has a lower threshold and an upper limit fluence which values depend on the material. The lower value is equivalent of the ablation threshold of the sample, below which the etch does not occur. In accordance with our assumption the upper limit corresponds to the ablation threshold of the particulate impurities which are responsible for the formation of cones, because these impurities remove from the surface of the polymers with the other ablating fragments when the fluence exceeds the upper limit. The dependence of the apex angles of the cones on the fluence and the number of pulses is investigated. A simple etching model based on the diffraction and interference theories is proposed to explain the formation of the conical structure.

A successful enhancement of sticking of PTFE is demonstrated using ArF excimer laser irradiation in the presence of novel photoreagents. The applied laser fluence was very low at the sample - photoreagent liquid interface compared to the energy density applied in earlier investigations. After the treatment the PTFE films were glued by epoxy resin. It was found that at low doses the tensile strength of the sticking increased rapidly with the UV pulse number and the reached a saturation value, which was 6.66 MPa for triethylamine, 5.56 MPa in the case of 1,2-diaminoethane and 4.64 MPa for triethylene-tetramine. These are around two hundred times higher than the value of the untreated surface. It was found that this procedure makes the metallization and painting of PTFE surface also possible. A photoinduced electron transfer mechanism was suggested to describe the photoreaction, which is responsible for the increase of adhesion features on PTFE surface.

In this paper experimental results in high-precision processing of various materials carried out with a 10 W copper bromide laser are presented.

A high brightness x-ray source has been obtained by focusing the large aperture excimer laser HERCULES on a solid target with a laser intensity of more than 10¹³W/cm². The characteristics of the x-ray source for different laser time evolution in the range 6-120 ns are investigated. Experimental result on specific applications of the source, like the soft x-ray contact microscopy and the low photon energy radiobiology will be presented.

We report on the use of an epoxy novolac chemically amplified photoresist, to get x-ray images of living biological species in the water window of soft x-rays. This photoresist response was at least two orders of magnitude 'faster' than the standard used PMMA in contact x-ray microscopy. Atomic force microscopy of the resist, relief images obtained with biological specimen masking, suggests a resolution better than 300 nm in lateral dimensions - the size of the cell flagellas - and 20 nm in depth profiles.

Photodynamic tumor diagnosis and therapy is efficiently carried out by endogenous protoporphyrin IX as photosensitizer, induced by external addition of the precursor 5-aminolevulinic acid (ALA). In the present study, PpIX localization and photodynamically induced damage was investigated in normal and transformed human fibroblasts. PpIX formation reaches its maximum after incubation for at least 20 h with 700 (mu) g/m1 ALA, and increases with the pH- value. ALA has to be given 20-30 times more than external PpIX in order to produce the same cytotoxic damage. As detected by Low Light Imaging, PpIX is generated in the mitochondria, released to the cytoplasm and distributed to cytoplasma and nuclear membranes.The nucleus is not stained. Intracellular targets of PpIX damage after irradiation are mainly mitochondria, ER and nuclear membrane. The organelles show a decomposition pattern, which resembles apoptotic morphology and occurs faster in the co-cultivated transformed than in the normal cells. ALA-treated hepatocytes produce micronuclei and chromosomal aberrations, which indicates some mutagenic potential. Expression studies of the (proto)oncogenes c-myc and bcl-2 sublethally treated fibroblasts by quantitative RT-PCR show high deviations from the constitutive expression level, which are accompanied by cell cycle disturbances, indicating a possible precursor role to apoptosis introduction.

The effectiveness of photodynamic treatment modality has been proven experimentally for a large variety of tumors, during the last years. This therapy utilizes the combined action of light and photosensitizing drug. Until now, a disadvantage of PDT has be the low tissue penetration of light, at the wavelengths of most commonly available lasers, for clinical studies. The red wavelength offers the advantage of increased penetration depth in tissue, in addition several new wavelength offers the advantage of increased penetration depth in tissue, in addition several new photosensitizers present absorption band at the region 630nm to 690nm. The development of high power red diode laser system for photodynamic therapy, has provided a cost effective alternative to existing lasers for use in PDT. This paper will describe the system design, development and performance of a diode laser system, connected with a fiber optic facility, to be used for PDT. The system was based on a high power semiconductor diode laser emitting at 655nm. The laser output power was approximately 60mW at the output of a 62.5/125/900 micron fiber optic probe. FUll technical details and optical performance characteristics of the system will be discussed in this paper.

Photodynamic therapy (PDT) is a promising new treatment for a variety of malignant tumors. Recently, PDT has been investigated as an alternative treatment for pancreatic carcinoma. The selection of photosensitizer and laser light are equally important for the treatment efficacy. The purpose of this study is to evaluate drug and light dose dependence of photodynamic effect in pancreatic cancer cells. Zinc tetrasulfonated phthalocyanines used as photosensitizer and a novel diode laser system terminated at alight shaping diffuser was used as light source. Viability was measured 24 and 72 hours after treatment and almost 100 percent lethality levels were achieved, by using low light doses independently of drug concentration. The results are discussed in correlation with light and drug doses.

PDT cytotoxicity is likely to occur through photooxidative reactions. In that way mechanisms that define poor oxygenation should be involved in defining resistance to photo-dynamic treatment (PDT). On the other hand bcl-2 anti- apoptotic protein has been shown to delay cell death and protect cells from toxic oxidative products. We examined 134 specimens from T1,2-NO,1 staged patients treated with surgery alone. Specimens were immunohistochemically examined for vascular grade using the JC70 MoAb, and bcl-2 oncoprotein expression. Bcl-2 expression correlated with low vascular grade. Only 3/27 of bcl2+ case had high angiogenesis vs. 34/107 of cases without bcl-2 expression. In the present study we provide evidence that bcl-2 overexpression directly suppresses angiogenesis in non-small cell lung cancer, which obviously results in decreased blood supply and oxygenation. This finding implies that reduced intratumoral angiogenesis and immortalizing oncoprotein overexpression are linked to each other and may have a role in defining tumors resistant to PDT.

In the last few years, there has been an increasing interest for the 3.0 micrometers laser radiation, as this wavelength is very strongly absorbed by the water and the other components of soft and hard tissue, in various medical applications, as soft tissue treatment, atherosclerotic plagues removal, treatment of eye lenses, vitreous surgery, hard tissue treatment, bone cutting and drilling, dentistry applications, etc. For all these medical applications reliable lasers emitting in the 3.0 micrometers wavelength range are needed and thus an intensive development effort is going on throughout the world. Our laser development effort, with the Er:YAG and the HF lasers, the only lasers emitting in the 3.0 micrometers wavelength part of the spectrum, in N.T.U.A., is briefly described in this article. For each one of the above possible medical applications, a demand for good flexible delivery systems, for pulsed Er:YAG or continuous wave and pulsed HF laser radiation arises. Several research groups around the world have suggested some possible solutions and among them are sapphire fibers, zirconium fluoride glasses, hollow metallic waveguides, hollow dielectric waveguides, hollow plastic waveguides, etc. In this paper we present the transmission properties of dielectric coated silver hollow glass waveguides fabricated in Japan, dielectric coated quartz waveguides and hollow plastic waveguides fabricated in Israel, sapphire fibers fabricated in USA, and fluoride glass fibers fabricated in France, we compare their straight and bent loss characteristics and we discuss their potential in the above mentioned medical applications.

The earlier investigations showed that the corneal haze can be due to the scattering effect of the excimer laser induced surface structure. In this paper a comparative study is presented regarding the development of these. Several human corneas were irradiated by an ArF excimer laser. The applied fluence was 193 mJ/cm². The developed surface structures after each excimer pulse were investigated by an atomic force microscope under physiological salt solution in natural environment. It was found that the structures of cells and fibers forming the cornea were observable on the ablated surface in the form of surface roughness. Scanning electron microscopic observations were also performed to compare the two surface investigation methods. It was found that this showed the same structures, but differently from the atomic force microscopic observation some distortions appeared produced by preparation processes of the samples, which were necessaries for the electron microscopic investigations.

The goal of this study is to further clarify the influence of the laser parameters on the safety of excimer laser angioplasty and to demonstrate the potential of XeCl laser to be a probe and a fire source simultaneously. On the base of a simple model it is demonstrated that the heat accumulation effects in the XeCl laser irradiated tissues is dependent on the ratio of the laser pulse repetition rate and the tissue thermal diffusion time and that there would not be a thermal injury of the tissues for pulse repetition rates under 15Hz. It was demonstrated that with a specially designed for use with optical fibers and a XeCl excimer laser angioplasty system fluorometer the real time diagnosis of vascular diseases and the feedback control for efficient and safe excimer laser angioplasty are possible.

This work is focused on the measurement of glucose in various diluted solutions and aims to be implemented in testing the glucose content in the anterior chamber of the eye by means of an electro-optic modulation method. By using solutions containing only glucose concentrations, a calibration curve displaying the dependence of the glucose concentration on a DC field, applied to a modulator, was obtained.

In the paper there have been proposed methods for increasing the accuracy of spectronephelometrical investigations of medical objects. This method is based on the measurements, that use the combination of the same apparatus blocks and their different positioning. The distinctive feature of the discussed methods is their stability to the changes of apparatus constants, the pollution of the optical components, as well as the elimination or minimization of the used a priori information or assumptions about the object. The efficiency of diagnostics of the blood formed elements by the developed methods was estimated.

The wide use of laser pointers must be compatible to the national and international 'avoid hazards' rules. Thus the owners and users of these lasers must follow all the safety standards, in order to avoid an ocular over-exposure to themselves or to the near audience persons. Many users are not laser specialists and do not know all the safety procedures or the exposure limits. For an average user the meaning of the warning label is not so clear, he may understand the wavelength and the output power, but what is the class of the laser. The word 'danger' in the pointer's label is clear, but for some young persons is the motive to use the pointer as the optical 'weapon' against the eyes of other people. The subject of our report is the identification of some hazard situations on the pointers use, starting with the basic hazard analysis, followed by application of optical metrology with calculations and measurements of the exposure levels and ending with the comparison to the maximum permissible exposure limits, in order to make clear that in some applications the hazard is a strong possibility. Thus a specialist consultant may take the advantage from our results and explain to the users that the laser pointer must be used with all the safety procedures and with the necessary care.