Here, we report a comparative experimental investigation about the radiation sensitivity of Long Period Gratings (LPGs), fabricated in several optical fibers (from standard to radiation hardened ones) by electric arc discharge technique. For the purpose, similar set of gratings were tested under two different conditions. One is gamma radiation produced by a 60Co source using a 0.2 kGy/h dose rate and up to 25-35 kGy total doses. The other is mixed neutron-gamma exposure in a nuclear reactor at 9 Gy/s gamma-rate and 1.25∙1012 n/(cm2 ∙s) neutron flux, reaching a total gamma dose of about 65 kGy and neutron fluence of 9.18∙1015 n/cm2 . The analysis was focused on the real-time radiation-induced wavelength shift exhibited by the gratings. As an outcome, the responses of the LPGs subjected to the different radiations were compared and correlated with fiber compositions.
We have studied the influence of gamma rays on physical properties of different commercially available silica optical
fibers stepwise irradiated up to a total dose of 100 kGy. The detection of radiation-induced changes in silica glass offers
the possibility of using selected optical fibers as distributed radiation sensors. The measurements performed by us were
based on optical backscatter reflectometry and Brillouin distributed sensing. The measurement methods enable an
analysis of radiation-induced modification of the group refractive index and density of the optical fibers. The most
distinct physical effect observed by us concerns the increase of the optical attenuation with rising total radiation doses.
Quantitative measurement results indicate a crucial impact of fiber dopants on radiation-induced physical and sensory
characteristics of silica optical fibers affected by differences in fiber fabrication techniques. Based on the obtained
results, the suitability of distributed Brillouin sensing for dosimetry applications seems to be improved by modifying the
refractive index profile of the fiber core.
In this work, we present long period gratings (LPGs) in two different Fluorine-doped fibers realized by electric arc
discharge (EAD) technique. Firstly, we optimized the EAD fabrication procedure for standard Ge-doped fibers where we
are able to fabricate relatively short LPGs with deep attenuation bands (up to 32 dB) and trivial power losses. Successively,
for the first time to the best of our knowledge, we produced LPGs in F-doped fibers with maximum attenuation band depths
in range 25-30 dB and trivial power losses. We also investigated the sensitivity of LPGs fabricated in such F-doped fibers,
with surrounding refractive index (SRI) and temperature changes, and compared the results with those of LPGs fabricated
in standard fiber. We found that SRI response of LPGs in F-doped fibers is significantly higher than in standard fiber and
it strongly depends on the type of F-doped fiber considered, whereas they exhibit a slightly lower sensitivity to temperature
compared to LPGs in standard fiber.
The sensitivity of low-loss perfluorinated polymer optical fiber (PF-POF) to gamma radiation is investigated for on-line
radiation monitoring purposes. The radiation-induced attenuation (RIA) of a commercial PF-POF based on Cytop material
is measured in the visible spectral region. The fiber RIA shows strong wavelength dependence with rapid increase towards
the blue side of the spectrum. The wide range of radiation sensitivities is available via careful selection of appropriate
monitoring wavelength. The accessible sensitivities span from 1.6 ± 0.2 dBm-1/kGy measured at 750 nm to
18.3 ± 0.7 dBm-1/kGy measured at 420 nm. The fairly high radiation sensitivity as well as its wide tunability makes the
fiber a promising candidate for a broad range of applications.
We report results from a wide range of laser operating conditions, typical for laser induced breakdown spectroscopy (LIBS) and laser ablation (LA) experiments on copper metallic target, which form the basis of further systematically investigation of the effect of laser irradiance, pulse duration and wavelength, on the target, plume and plasma behavior, during and after laser-solid interaction. In the LA experiment, the laser beam was focused through a 25 cm focal length convergent lens on a plane copper target in air, at atmospheric pressure. The target was rotated in order to have fresh areas under laser irradiance. In the LIBS experiment, the Applied Photonics LIBS-6 instrument allowed modifying the laser irradiance at the sample surface by changing the pulse energy or the laser focusing distance. For the duration of the laser pulse, the power density at the surface of the target material exceeds 109 W/cm2 using only a compact laser device and simple focusing lenses. The plasma parameters were experimentally estimated from spectroscopic data generated by the plasma itself, namely by the line intensities and their ratio which reflect the relative population of neutral or ionic excited species in the plasma. The fitting of the Saha-Boltzmann plot to a straight line provides an apparent ionization temperature, whose value depends on the lines used in the plots. For the typical conditions of LA and LIBS, the temperature can be so high that Cu+ ions are formed. The first-order ionization of Cu (i.e., the ratio of Cu+/Cu0 ) is calculated.
In this paper, we report the results concerning electron beam irradiation of mid-IR windows and mid-IR detectors for possible use in trace gas detection systems, in the 1 μm to 5 μm spectral range under ionizing radiation conditions. Four windows materials (CaF2, BaF2, ZnSe, and sapphire) for the mid-IR were tested as they were exposed to electron beam irradiation at a dose rate of 4 kGy/min, for doses from 0.5 kGy to 2.2 kGy. Two IR detectors (photoconductive – PbSe, photovoltaic – InAs) were subjected to the same type of irradiation at dose rate of 4 kGy/min, in three subsequent exposures, for a total dose up to 6.8 kGy. Before the irradiation and after each irradiation step the windows were measured as it concerns the spectral optical transmittance, spectral optical diffuse reflectance, and, in the THz range (0.06 THz – 3 THz), the dielectric constant and the refractive index were evaluated. THz imaging analysis of the irradiated samples was done. For the IR detectors we measured at different irradiation stages the spectral responsivity and the dark current. The most affected by electron beam irradiation was the CaF2 window, in the spectral interval 250 nm – 800 nm. The spectral transmittance of the four windows remained unchanged after their exposure to ionizing radiation in the near-IR and mid-IR. Noticeable variations of the spectral responsivity appeared upon electron beam irradiation in the case of the InAs detector.
Two Organic Photovoltaic devices having a photoactive layer containing Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5- (4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM, 99%), and the layer sequences – glass/ITO/ZnO/PAL/PEDOT:PSS/Ag/encapsulation were non-destructively investigated by diffuse optical spectral reflectance, THz spectroscopy and THz imaging. The proposed methods proved to be powerful tools to support quality assurance in organic solar cells development, facilitating both the localization of manufacturing defects and the device degradation, as they are combined with “classical” evaluation means.
In this paper, we present the first results regarding the on-line monitoring of gamma-ray exposure effects on a commercial multi-mode perfluorinated polymer optical fiber (PF-POF), type GigaPOF-50SR from Chromis Fiberoptics. Our focus was to evaluate on-line the radiation induced attenuation (RIA) over a wide spectral range (320 nm – 1700 nm), in order to assess the fiber’s radiation hardness and its possible use in radiation detection. An Ocean Optics QE65000 high sensitivity spectrometer and a StellarNet near-IR spectrometer were used to cover the spectral ranges 200 nm – 1μm and 900 nm – 1.6 μm, respectively. Electron paramagnetic resonance was used to monitor the recovery of the irradiation induced centers at room temperature. The study indicated that the optical fiber can be used as radiation monitor at low dose rates by measuring the attenuation in the UV, while higher dose rates irradiation can be observed by RIA monitoring at specific wavelengths in the visible spectral range.
We report the evaluation of one long period grating (LPG) and one fiber Bragg grating (FBG) under gamma irradiation. The LPG was produced by the melting-drawing method based on CO2 laser assisted by a micro-flame and was engraved in a commercial single mode fiber SMF28 from Corning, grating length 25 mm, grating pitch of 720 μm. After the manufacturing of the grating, the fiber was re-coated with Acrylate and the grating was inserted into special ceramic case transparent to gamma radiation. The FBG is commercialized by Technica SA, and it is written in SMF-28 optical fiber (λ= 1546 nm; grating length of 12 mm; reflectivity > 80 %; bandwidth – BW @3 dB < 0.3 nm; side lobe suppress ratio – SLSR >15 dB; Acrylate recoating). By on-line monitoring of the LPG wavelength deep with an optical fiber interrogator during the irradiation exposure and pauses, both the irradiation induced shift (maximum 1.45 nm) and the recovery (in the range of 200 pm) phenomena were observed. Temperature sensitivity of the LPS was not affected by gamma irradiation.
We report the first demonstration of single-mode laser beam delivery in hollow-core waveguides (HCWs) operating in the 3.7-7.3 μm spectral range. We investigated the transmission properties of HCWs with 200 μm bore diameter and internal coatings properly designed to enhance the spectral response in the spectral range of 3-12 μm. We achieved single mode output throughout the 3.7-7.3 μm range. We measured a coupling efficiency < 90% and transmission losses as low as 1 dB, when using a 15 cm-long fiber at 3.7 μm under optimized coupling conditions between input beam and HCW.
A PMMA based plastic optical fibre sensor for use in real time radiotherapy dosimetry is presented. The optical fibre tip is coated with a scintillation material, terbium-doped gadolinium oxysulfide (Gd2O2S:Tb), which fluoresces when exposed to ionising radiation (X-Ray). The emitted visible light signal penetrates the sensor optical fibre and propagates along the transmitting fibre at the end of which it is remotely monitored using a fluorescence spectrometer. The results demonstrate good repeatability, with a maximum percentage error of 0.5% and the response is independent of dose rate.
A set of applications of interest for semiconductor lasers constitutes their use under irradiation conditions in nuclear power plants, radiation processing facilities, high energy physics accelerators, nuclear waste management sites, or even space crafts. One such an example is the task related to remote handling and control in fusion installations (i.e. ITER - the International Thermonuclear Experimental Reactor). The paper reports our results on the irradiation effects on different semiconductor laser structures, emitting at 850 nm, 1310, 1550 nm, as they were subjected either to gamma-ray (total dose of 1.5 MGy) or neutron irradiation (total fluence of 1013 n/ cm2 ), in the frame of the European Union's Fusion Program. The electrical, optical and optoelectronics characteristics (the optical power vs. the driving current of the semiconductor laser; the embedded photodiode current vs. the emitted optical power; the direct voltage vs. the driving current, the external quantum efficiency, the serial resistance, the photodiode responsivity) were monitored under these conditions. All the investigated devices were commercially available products. The irradiations were done at room temperature, and the measurements were carried off-line.
In the frame of the European Union funded Comenius project "Hands-on Science", a network of very active high schools
was created, aiming to attract students towards science study by offering them the possibility to learn and to express
themselves through experiments. On the other side, our Institute coordinates the project "Science Education and Training
in a Knowledge-Based Society - SET 2010", project supported by the Romanian Ministry of Education and Research,
which targets the same audience by different means. The paper addresses some of the results of these two projects as they
are linked with photonics teaching in high schools through extra curricular activities such as science clubs, science fairs, and
national contests for high school students. The project results were introduced to the public at various conferences: ETOP
Conference (France), NATO Advanced Workshop (Hungary), Hands-on Science Conference (Greece), Euroscience Forum
(Germany), Communicating European Research (Belgium).
The paper presents a comparative study, by off-line measurements of the irradiation induced optical attenuation in
several large diameter (600 μm) optical fibers subjected to gamma-rays and neutron irradiation. The optical fiber samples
fall into two categories: optical fibers with an enhanced UV transmission (high OH content core) and solarization
resistant optical fibers. The irradiation conditions were as follows: a) gamma irradiation at a 60Co source, with a dose rate
of 0.33 kGy/h +/- 5%, up to the maximum total irradiation dose of 313 kGy; b) neutron irradiation (mean energy 5.2
MeV) using a deuteron beam (13 MeV) and a thick beryllium target, for a total fluence of 6x1012 n.cm-2. Electron
paramagnetic resonance measurements have been carried out to further investigate the radiation sensitivity of the
considered fibers and to identify irradiation induced paramagnetic point defects.
KEYWORDS: Photonics, Education and training, Physics, Professional development courses, Internet, Mathematics, Chemistry, Fiber optic communications, Biology, Sun
From 2004, the Center for Science Education and Training (CSET) participated to the European Union-funded educational network "Hands-on Science". The aim of the Romanian team was to transform teachers and students from end-users of educational aids to active designers and developers of instructional materials. Several science fields were identified, including photonics. The team at CSET is now focusing on: lasers and their applications, optical fiber communications, solar energy as a sustainable source, and the use of optical spectroscopy in physics and chemistry. CSET initiated an international collaboration with the New England Board of Higher Education (NEBHE) in Boston, Mass., when the Center enrolled an experienced Romanian high school science teacher in a twelve-week “Introduction to Photonics” laboratory-based professional development course. The course was developed by NEBHE through an Advanced Technological Education (ATE) program grant from National Science Foundation and is designed for high school and community college educators from both science and technology instructional areas. The paper reports the experience of this international participation which was made possible since the course is delivered via the Internet by Three Rivers Community College, Norwich, Conn. Its impact on photonics education in Romania and the USA is analyzed, as the participant teacher shares her experiences with teachers and faculty in the “Introduction to Photonics” course and with those enrolled into the Romanian “Hands-on-Science” program.
This paper describes the necessity and the procedures for power calibration transfer at different laser wavelengths, and particularly in the range 9.2-10.8 μm where CO2 lasers emit. To accomplish this purpose, the reference laser must be very well characterized, especially regarding its frequency and power instabilities. We have designed and built a line tunable, frequency and power stabilized sealed-off CO2 laser operating in continuous wave and we have measured the operating parameters, such as tunability, frequency instability and power instability in different experimental conditions. The laser was optimized to work as a reliable reference instrument for power calibration transfer.
In the Society of our days there is a major increasing need of an in depth quality education in Science and Technology. Science teaching at school should be generalized aiming not only the sound establishment of a "Science" culture in our societies but also to guarantee a steady basis for the improvement of Science and its technological applications. The European Commission, under the program Socrates, Comenus 3 action (project n°. 110157-CP-1-2003-1-PT-COMENIUS-C3) supports the network "Hands-on Science". The activities of our network focus on the development and or diffusion at European scale of positive hands-on experimental practices on teaching science at basic secondary and vocational training schools, by leading the students to an active volunteer and committed participation in the teaching/learning process through hands-on practice and experimentation, making intensive use of the new instruments and resources of the Information Society.
We are reporting the investigation on the degradation of heterojunction laser diodes as they were subjected to electron beam irradiation. The research was done under the European Union’s Fusion programme, and targets the possible use of semiconductor lasers for remote sensing and robotics, under irradiation conditions. A total irradiation dose of 90 Mrad was achieved at room temperature, and the irradiation geometry was an axial one. The measurements were performed off-line. An automatic measuring set-up was developed including various instruments: a laser diode driver, a laser power meter, a wavelength meter, a fiber optic spectrometer and a laser beam analyzer. After each irradiation step, the following characteristics were monitored, as function of the driving current and laser case temperature: the emitted optical power, the wavelength of the emitted radiation, the embedded photodiode current, the longitudinal and transversal mode structure, as well as the temporal behavior of all these parameters. For each irradiation dose, the laser diode serial resistance, threshold current, and quantum efficiency, and the photodiode responsivity were plotted for different operating conditions (extended graphical information is provided in the paper). The following changes were noticed: an increase by 6 % for the threshold current, a drop by 7 % for the quantum efficiency, a decrease by 9 % for the photodiode responsivity, and a slight modification of the wavelength of the emitted radiation.
A new therapy laser device is presented. The device consists of a central unit and different types of laser probes. The laser probe model SL7-650 delivers seven red (650 nm), 5 mW diode lasers convergent beams. The beams converge at about 30 cm in front of the laser probe and the irradiated area might be varied by simple displacement of the laser probe with respect to the target. The laser probe SL1-808 emits single infrared laser beam up to 500 mW. The efficiency of the use of this device in physiotherapy, and rheumatology, has been put into evidence after years of testing. Dermatology and microsurgery are users of infrared powerful laser probes. The device has successfully passed technical and clinical tests in order to be certified. The laser device design and some medical results are given.
Commercial available red and infrared diode lasers have been tested. A set of ten pieces of red 25 mW nominal output power and five pieces of 0.5 W infrared diode lasers have been investigated. The laser output power has been measured by using an Ophyr power-meter. Ophyr F150 head (3mW noise) was used for power measurements of the infrared diode laser and Ophyr 3A-IS integrated sphere was used in the case of red diode lasers. A Spiricon laser beam analyzer was used to determine the beam intensity distribution. An API wave-check wavelength meter measures the wavelength of the diode lasers. Temporal behavior of the diode lasers over periods of days was recorded. The influence of ambiental conditions is considered. Our study guarantees the proper choice of the diode laser to be used in specific applications such as medical, and industrial applications.
The characteristics of laser diodes (wavelength of the emitted radiation, output optical power, embedded photodiode photocurrent, threshold current, serial resistance, external quantum efficiency) are strongly influenced by their driving circumstances (forward current, case temperature). In order to handle such a complex investigation in an efficient and objective manner, the operation of several instruments (a laser diode driver, a temperature controller, a wavelength meter, a power meter, and a laser beam analyzer) is synchronously controlled by a PC, through serial and GPIB communication. For each equipment, instruments drivers were designed using the industry standards graphical programming environment - LabVIEW from National Instruments. All the developed virtual instruments operate under the supervision of a managing virtual instrument, which sets the driving parameters for each unit under test. The manager virtual instrument scans as appropriate the driving current and case temperature values for the selected laser diode. The software enables data saving in Excel compatible files. In this way, sets of curves can be produced according to the testing cycle needs.
In this paper we report original results related to the degradation of laser diodes parameters, as they are subjected to electron-beam and gamma-ray irradiation. For this purpose, we investigated two double heterostructures laser diodes, operating at 808 nm, 850 nm respectively. The maximum emitted optical power was in the range of 5 -6 mW, in CW operation mode. Radiation induced modifications of laser diodes electrical, optoelectrinc and optical parameters were studied. Simultaneously, the responsivity of the embedded photodiode was monitored. Slightly changes in the laser threshold current, emitted radiation wavelength, serial resistance and external quantum efficiency were observed, while more important variations of the photodiode responsivity and laser diode spectral distribution were noticed. The temperature dependence of device parameters after the irradiation was also studied. The work under way is performed in the frame of EU’s Fusion Programme.
Several low power medical laser devices were studied. We focused on power, wavelength and beam characteristics (2D and 3D images, point stability, beam profile, gaussian fit and elliptical axis etc). The variation of laser parameters for different time intervals and room temperatures was studied.
It is of great importance from the experimental point of view, to understand the thermal behavior of the optical components during how power/energy laser irradiation. The study of the heat transfer in the sample volume is necessary in designing and manufacturing high quality optical components. In this context, we discuss the surface heat transfer coefficients influence on the temperature profile, during CO2 laser irradiation of homogeneous optical components. The assumption of zero heat transfer across the sample radial longitudinal sections is also analyzed. Thermal profiles deduced from the heat diffusion equation are plotted for different heat transfer values.
Laser products for medical or industrial use have to be evaluated both for their performances (output power/energy power/energy density, bean characteristics, etc.,) and from laser safety point of view. This paper presents an integrated setup for characterization of the laser systems, by connecting, through a dedicated software, stand alone measurement devices. In our set-up two Spiricon laser beam analyzers: LBA 100 and LBA 300-PC as well as an Orphir LaserStar power/energy meter work under a PC control. Some of the software involved was developed by using the LabVIEW 5.0 graphically programming environment, and allows the user to remotely control the measurement process by virtual instruments.
At the European scale, a new strategy practice was developed, in relation to the New Approach. The EC Directives require manufactures and users to carry out risk assessment of the product and/or the working place, respectively. Until now, in Romania there were no conditions referring to a qualified protection concerning laser hazards, neither from legal, nor from technical point of view. The paper refers to the efforts devoted in the last years to overcome these drawbacks, in connection with: the preparation of national standards, the participation to international activities related to the development of written standards, the organization of courses/seminars on laser safety, and the structuring of a national facility for laser metrology. The talk describes how these activities were supported by some European programs, or bilateral cooperation with partners from Western European countries.
Studies on beam power behavior in time and laser beam mode structures of laser diodes/LEDs used in low level laser therapy (LLLT) were performed. Two laser diodes with cw emission in red at 635nm, a cw laser diode emitting in IR at 904nm and 2 LEDs which emit radiation at 904nm, respectively 650nm were analyzed from the point of view of the beam power, 3D, 2D distributions and the variation of radiation intensity in time. A laser beam analyzers, model LBA-100 was used for laser beam profile studies. The time behaviors of the lasers/LEDs beams intensity were achieved with a LASERSTAR energy meter, OPHIR OPTRONICS. These studies are very useful for establishing the appropriate irradiation doses and procedure for LLLT.
This paper present a new computing procedure for measuring the bulk absorption coefficient of the laser optical components that present a layered structure as the coated otpical components. Previously, this measurement has ben conducted usually by laser calorimetry with the procedures provided by ISO 11551. However these methods assume the probes to be homogenous and for the inhomogeneous samples this assumption may introduce significant errors in the value of the absorption coefficient. The method is based upon the general solution of the heat diffusion equation calculated for an optical component irradiated by a laser beam with all parameters known. Because the optical component has a layered structure, in order to obtain the solution of the mentioned equation in each layer, a system of heat equations has to be solved. The solutions of this system correspond to the diffusion in each layer and they strongly depend upon the absorption coefficient of each layer. Due to the fact that the values for absorption coefficient are small for the studied samples, these solutions are developed in Taylor series with respect to the absorption coefficient. This development leads to a set of algebraic equations that provides the absorption coefficient value of each layer if the temperature in one point of that layer is known. This method has been experimentally tested by evaluating the absorption coefficient of a ZnSe sample with an AR coating of BaF2 and the result proved to be in agreement with the results obtained by numerically simulating this process.
LabVIEW is a consistent development and execution environment that provides a method to implement various test and measurements' systems containing stand alone laboratory instruments. This paper describes a virtual instrument created in LabVIEW that facilitates the control of a dual channel laser power/energy meter through a computer serial port, for accurate laser power/energy data logging and handling. The program has a modularity structure and could be easily used in conjunction with the device in any application involving laboratory laser power/energy measurements. The program was tested with very good results for the characterization of different types of lasers.
In this paper the applications of holographic interferometry to ionizing radiation dosimetry are presented. The determination of the accurate value of dose delivered by an ionizing radiation source (released energy per mass unit) is a complex problem which imposes different solutions depending on the experimental parameters and it is solved with a double exposure holographic interferometric method associated with an optoelectronic interface and Z-80 microprocessor. The method can determine the integral absorbed dose as well as the tridimensional distribution of dose in a given volume. The paper presents some results obtained in radiation dosimetry. Different transparent liquids were used as ionizing radiation transducers. Integral dose and spatial dose-distribution were recorded for equivalent tissue liquids and blood plasma. Boundary phenomena, during a irradiation of successive layers of liquids having different atomic numbers, were investigated.
The algorithms developed can be used for any application, which requires tridimensional visualization and additional processing of experimentally acquired images. This paper especially refers to image processing and visualization in laser beam analysis. The information, acquired by a CCD camera and stored as a matrix of gray levels, is processed and the result is a 3-D representation of the beam intensity profile. An interpolation-and-averaging method (independent of the matrix dimensions) was developed, aiming at reducing the time required for data representation in on-line applications and also to diminish the camera noise and sampling errors. The experimental works were performed using a COHU 4913 camera, connected to an LBA-100 laser beam analyzer, which were coupled to a PC compatible computer. Several lasers, such as He-Nw, He-Se, pulsed and cw Nd:YAG lasers, laser diodes, and laser diode arrays, operating at different wavelengths, were studied. The developed algorithm was implanted on the computer, so that the overall system performances were improved, obtaining a user-friendly interface for data visualization and further processing.
Two Fresnel birhomb (lambda) /4 retarders have been realized from glass and fused quartz respectively, both having identical geometrical parameters but different residual stress birefringence of the raw material. Their behavior as achromatic retarders were examined in a null spectroscopic ellipsometer. The way in which the performances of this type of retarder depend on the residual stress birefringence is presented.
We have developed a laser-diode pump system for continuous-wave end-pumping of Nd:YAG lasers. The pump system includes a pair of 1 W diode-arrays mounted in coaxial enclosures, a driver unit and the pump optics. The array wavelength was temperature tuned to achieve the maximum absorption of the pump radiation in the Nd:YAG crystal. The characteristics of the pump system are presented and the pump-beam profile is investigated.
The paper presents the theoretical background of laser calorimetry as a method to investigate the absorptance of optical components, according to the recently adopted ISO Standard 11 551. An experimental set-up for optical absorption measurements, including a cw CO2 laser and a calorimetric chamber, is presented. The calibration of the laser calorimetric set-up is also described. The calibration involved several steps: laser power calibration, evaluation of chamber sensitivity, electrical calibration using electrically heated samples and optical calibration utilizing 100% absorptance samples. There were measured the conversion factors for the laser power and for the sample temperature; there were calculated over-all correction factors for the different substrates and they could be placed within +/- 4% around their mean value.
The paper describes the methods used to adapt an industrial TEA- CO2 laser to the requirements of the ISO standard 11 254-2 for a laser induced damage threshold experimental facility. The goals were to improve the pulse energy stability and the laser beam spatial profile and the methods were: (1) finding the best discharge voltage; (2) adapting the laser cavity, (3) using suitable apertures. There is also presented the experimental set- up for beam characterization, which included a laser beam profiler (a line of 60 pyroelectric detectors), an energy-meter to monitor the pulse energies and KCl optical components for beam splitting and beam guiding. Every beam distribution was regarded as a linear combination of normalized Gauss-Hermite functions and the fitting algorithm allows the calculation of the coefficients of this combination.
The theoretical model for the heat diffusion in the case of a high power IR electrically calibrated laser powermeter, developed at the Institute for Atomic Physics in Bucharest, is presented. The IR laser beam falls onto a laser detector, a special design copper disc wafer which absorbs the laser beam, heats its center. A daisy-chain of thermocouple elements having one set of junctions thermally connected to the central region of the disc and the other ones to the disc's boundary is used to detect temperature rise induced by the exposure to the laser beam. For calibration, the copper disc is electrically heated and the electric power that produces the same temperature rise as one induced by an incident laser beam, should equal the laser beam power. The electric heater is designed to provide a uniform heating of the copper disc. The solution for heat diffusion equation was searched as a series of Bessel functions of zero order, the cold junction's temperature was imposed as boundary condition and the heat induced by the laser beam in the disc's center was regarded as input data. To find the correct solutions, there must be taken into account the designing elements of the copper disc: termic material's properties (caloric capacity, termic conductibility), laser detector's geometry, copper's density. The electric power for calibration was injected using a precision power injection circuit which allows a stability of the calibration power, better than 0.1%.
A simplified formula to accurately compute the influence of the temperature, pressure and humidity on the refractive index of the air is deduced. It is studied also the contribution of the measuring errors of the air parameters (temperature, pressure, humidity) and of the object investigated by laser interferometry (expansion coefficient), to the final error of the measurement.
For high luminosity hadron collider experiments, the microstrip gas chamber (MSGC) seems to be the longtime expected position detector. Its high spatial resolution (tracks of less than 35 micrometers ), high rates (particle fluxes of about 106 s-1 mm-2), good time resolution (around 50 ns), proportional gain (2 divided by 5 X 103), guaranteed lifetime (about 20 years) strongly recommended it for further investigations. The purpose of this paper is to indicate preliminary results concerning the optical investigation of MSGC electrodes, in order to check-up their quality both at the end of manufacturing process and after their use. The optoelectronic control device used for MSGC electrodes' evaluation is described.
Two high accuracy, high productivity measuring devices for checking mechanical products in fine mechanics factories are described. The first one enables the evaluation of the mechanical characteristics of dial indicators. The second is dedicated to metrological checking of graduated rules, used as length standards for the traveling parts of machine tools. The operating principle as well as the parameters of both devices are given.
The paper reports the results obtained at the Institute of Atomic Physics, Department of Laser, in the field of absolute measurements of laser radiation. For the IR range of wavelengths an electrically calibrated detector was developed. For the visible laser radiation a Romanian made, predictable quantum efficiency silicon detector was used, which was compared with similar detectors provided by the National Institute of Standards and Technology, during an international intercomparison.
Graduating rules used as length etalons in optical measuring instruments and tools need to be checked for graduation accuracy. The best way to perform this is by using a laser interferometer as a linear displacement transducer, some specially designed optoelectronic interfaces, and a computer for control and data processing. Implementation of measuring equipment consisting of these assemblies is described below.
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