Optical Diagnostic Systems Research Articles

Sidney N. Stone (1922–2011)

Stone was a scientist at Los Alamos National Laboratory who conducted defense related research such as the ionospheric effects of rocket exhaust and optical diagnostic systems for laser-produced shock waves.

Structural analysis of large-scale SS collecting mirrors for ITER diagnostics

ITER is a nuclear fusion research and engineering project. It is supposed to be the first fusion device designed for testing the integrated technologies, materials, and physical aspects necessary for development of the commercially available fusion-power plant. One of the important components of the project is optical diagnostic systems with collecting mirrors. These mirrors have to provide stability of optical systems under severe loads of different types that could possibly arise in the tokamak. The collecting mirrors of several ITER diagnostics have a large scale and should be installed into diagnostic ports. Thermal stress analysis of the mirror updated design is aimed to obtain deformation and rotation values of the mirrors’ reflecting surfaces in order to conduct ray tracing analysis and to edit mirrors alignment to provide correct functioning of the optical systems. The maximum temperature values of the Divertor Thomson Scattering collecting mirrors were estimated for the normal operation mode. The FE model of the second mirror takes into account all the force boundary conditions, basic kinematic boundary conditions and constraints. Boundary conditions taken for the simulation were applied on surfaces contacting with the diagnostic rack. Thermally stressed state was calculated and corresponding displacement and rotation distributions were obtained.

RF circuit analysis for ITER visible spectroscopy reference system first mirror plasma cleaning

The Visible Spectroscopy Reference System (55.E6.VSRS) is going to be one of the first optical diagnostic systems in the ITER tokamak chamber, for which plasma cleaning system of front-end optics has to be implemented. In order to extract light out of the fusion plasma towards diagnostic sensor systems, a set of optics forming a labyrinth will be employed. The VSRS front-end contains a 100 mm diameter first mirror (FM) that is expected to experience contamination with beryllium and tungsten degrading its performance. To maintain or restore the FM optical performance, a high-frequency-discharge-based plasma cleaning system will be implemented. The high-frequency power transmission circuit will contain four parallel mineral insulated radio-frequency (RF) cables, pre-matching elements, signal splitters and a number of interfaces. The circuit ends with the FM, where plasma is ignited in front of it. The FM is combined with the RF power electrode. The whole RF signal transmission circuit is modelled based on realistic characteristics of RF components such as cables and feedthroughs, their dimensions and ITER operational requirements. The goal is to understand the RF power budget, power distributions and losses in the components critical for the design. First simulation results confirm that the presence of a passive L-C pre-matching element next to the FM is critical for acceptable power consumption in the circuit. The results are also useful for other ITER optical diagnostics where RF plasma cleaning of the FM is foreseen and where similar power transmission circuits may be used.

Mathematical model of photoplethysmographic signal recorded in transmitted light

The use of near-infrared laser radiation is currently one of the most promising trends in the development of medical diagnostic research methods. The basic principle of operation of most optical diagnostic devices and systems is the interaction of the incident radiation with the biological environment under study, as a result of which the parameters of the light flux change. When choosing the principles of constructing optical measuring transducers parameters of biological tissue, it is necessary to take into account a number of its specific features as an object of research. The radiation of the optical range falling on the biological tissue under study is capable of influencing it, which manifests itself in the form of heating, additional photochemical reactions. This circumstance is due to the absorption of light, which occurs selectively in most cases. Therefore, the development of optical diagnostic devices and systems should be accompanied not only by taking into account the maximum intensity of the incident radiation, but also by analyzing its spectral composition, since the use of different wavelengths for the study of biological tissue is accompanied by different effects on the biological object and significantly different measurement results. When the light flux passes through biological tissue, its intensity is weakened as a result of absorption (absorption), reflection, scattering. In a number of thematic sources, the process of interaction of laser radiation with biological tissue is considered in detail and it is shown that it is characterized by a number of coefficients: specular reflection, absorption, scattered (diffuse) reflection, scattered (diffuse) transmission, directional transmission, which are completely determined by the following light fluxes: incident to the interface of media, diffusion reflection, reflected, diffusion transmission, directional transmission. It should be noted that the absorption and scattering of the light flux occurs selectively. Therefore, the quantitative characteristic of absorption is determined using monochromatic optical radiation with a strictly fixed spectral composition. This article discusses a photoplethysmographic diagnostic method, the key advantage of which is the ability to assess the dynamics of oxygen transport and consumption in the blood microcirculation system (determining the level of peripheral blood saturation). The low accuracy of the available mathematical models, which do not adequately describe the processes of interaction of optical radiation with biological tissue, should be attributed to the very topical problems of the application of this method. It should be said that there are two approaches to creating such models: analytical and simulation. However, analytical models make it possible to obtain more accurate values of the determined parameters, in contrast to simulation ones, which allow one to obtain only the probabilistic characteristics of their determination. Therefore, this article will use the analytical approach to model development.

RF discharge mirror cleaning for ITER optical diagnostics using 60 MHz very high frequency

• First mirror cleaning using 60 MHz very high frequency was optimized. • The pre-matching element is reducing the power consumption. • Cleaning homogeneity on a curved and large size mirror was measured. • End-of-Cleaning Indicator using Optical Emission Spectroscopy was demonstrated. For the fusion reactor ITER, a mandatory monitor of the fusion device and plasma will be performed with optical diagnostic systems. For the metallic first mirrors, the recovery of the reflectivity losses due to dust deposition is proposed to be carried out for 14 different optical diagnostic systems by the plasma cleaning technique. In this work, we studied the influence of the electrode area on the electrode potential as a function of the applied power with a 60 MHz radio very high frequency source. Unshielded copper disks with different diameters were constructed to study the impact of the electrode area in the range of 90 cm 2 to 1200 cm 2 , which corresponds to an Edge Thomson Scattering area ratio of 0.15 to 2. It was observed that the absolute value of the resulting bias decreased from 280 V to 15 V with the increase of the area for a given RF power. Moreover, the power consumption was reduced by 43 % using a pre-matching element close to the vacuum feedthrough. The cleaning homogeneity on a curved and a large size mirror was studied, and the difference between the center and edge maximum/minimum was around 20 % and 40 % for the curved and large size mirror, respectively. For ITER, it is required to have an End-of-Cleaning Indicator (ECI), which shows when the cleaning process would be stopped. In this work, we studied the feasibility of Optical Emission Spectroscopy (OES) as a real-time control tool for the RF cleaning process. With 13.56 or 60 MHz, it was possible to use OES as ECI by following the molybdenum (Mo), rhodium (Rh), and aluminum (Al) emission lines. The decrease of Al I line and increase of the Mo I and Rh I line were recorded as a function of the cleaning time.

Automated full-field polarization-sensitive optical coherence tomography diagnostic systems for breast cancer.

Intraoperative delineation of breast cancer is a major challenge. An effective breast tissue screening technique may reduce the risk of re-excision during surgery by specifically identifying positive margins. In this study, a high-resolution automated full-field polarization-sensitive optical coherence tomography (FF-PS-OCT) system was developed to classify healthy and malignant human breast tissue from quantitative phase retardation information of the tissues in ex vivo. Twelve breast tissue samples [four healthy, eight malignant (cancerous)] were imaged with the FF-PS-OCT system and the different phase features were extracted from the acquired OCT images (106), based on the differences in the optical signatures of the healthy and malignant tissues. A linear support vector model classifier was trained using 75 images, with a sensitivity of 92.10% and specificity of 89.18% was achieved. Thirty-one images were used to test the model, with a sensitivity of 90.90% and specificity of 85.0% achieved.

Investigations of the optical properties of enamel and dentin for early caries detection.

The aim of this study was to experimentally investigate the potential of different light wavelengths to distinguish between healthy and carious tissue using a two-circle goniometer. Tooth slices were prepared from extracted human teeth that were caries free (n = 15) or had occlusal caries lesions (n = 10). The tooth slices were irradiated with diode laser modules of different wavelengths (532, 650, 780 nm). The transmitted and scattered laser light was spatially measured with a detector rotating on a two-circle goniometer. The anisotropy factor and attenuation coefficients were calculated. Enamel was more transparent than dentin and showed wavelength-dependent attenuation. Healthy dentin showed strong light scattering at all wavelengths, independent of the tested wavelength. The calculated attenuation coefficients of carious and healthy tooth tissue differed significantly (p < 0.05; t test). In contrast to healthy enamel, carious enamel showed lower light transmission and an increase in scattering. Differences in the light attenuation of carious versus healthy dentin were less pronounced than those for enamel. Carious dentin was slightly more transparent than healthy dentin. The light of longer wavelengths showed a better penetration of all tooth structures compared with shorter wavelengths. Healthy and carious dentin and enamel exhibited distinct optical properties using laser light at different wavelengths. In dentin, changes in the optical properties caused by caries are significantly less pronounced. The clear distinction between healthy and carious enamel makes optical caries diagnostic systems ideal tools for early caries detection.

IMPROVEMENT OF METHODS AND TOOLS FOR OVERHEAD CONTACT LINES DIAGNOSTICS

This paper describes developments of tools and methods in a wear of contact wire aspect, based on optical diagnostic systems and computer vision. In general, such diagnostic systems contribute towards improved service quality, reduced costs and increased security in railways. The contact wire is an important part of the OCL. It interacts with the pantographs which are mounted on the roof of trains and moving at various speeds. It is subject to abrasion, friction, scraping, corrosion, erosion, vibration, arcing and welding at different degrees of severity depending on the wire and collector strip materials, modes of interaction and the environmental conditions that defines the wear of contact wires. Measuring systems which automatically detect the degree of wire wear are necessary in order to carry out efficient OCL infrastructure management and condition-based maintenance of contact wire. The problem of wear measurement characterized by some important determining factors like lighting conditions, background scenery and the disparity of reflexives properties of the contact wire. Besides, in order to conduct an efficient inspection, the measures have to be carried out in a changing speed of inspection train. Finally, an important issues for designing and developing measurement systems are the number of wire in measurement range. Systems have to be able to measure not less than four contact wires which are simultaneously in a range of vision and the contact wire geometric parameters such as height and displacement (stagger). The measuring systems have to acquire, process and store a considerable amount of data in real time. Due to the amount of information to be processed, a high-performance architecture and effective algorithms are needed for real-time monitoring. The hardware and software modernization of a high-speed laser system for a contact wire parameters measurements are examined. Such modernization is fulfilled mostly by implementing a real-time high-speed compression algorithms and using LED backlighting. The results of the measurement of the contact wire’s wear obtained by a modernized high-speed laser system during an inspection trips on a new modern laboratory-car are given in this article. Keywords:, optical diagnostic systems, LED emitter,overhead contact lines of railways

Medical control of a pulse wave fiber optic sensors

The modern level of development of systems of measurement, processing and data transmission promote creation of optical multiple parameter medical diagnostic systems. One of intensively developed directions is creation of fiber-optical diagnostic systems on the basis of fiber optic sensors. Fiber optic sensors are characterized by high sensitivity to mechanical oscillations of a surface of a body of the patient under power influence of a blood flow. This property creates premises for design miniature, steady against noises, safe sensors of micromovements. Their fixing on a body of the patient allows to reveal a number of the vital parameters characterizing normal and critical condition of the patient. Results of a research of fiber optic sensors of pressure on the basis of standard single-mode optical SMF-28 fiber are presented in article. The principle of operation of sensors consists in use of physical properties of the fiber - the impact which had in some pressure point on throughput characteristic. The purpose of the real work is the research of a possibility of use of fiber optic sensors of the tunnel, flexural and microflexural types on Bragg’s grid for control of a pulse wave providing more exact determination of parameters of a pulse wave. The offered monitoring systems of a status of patients on the basis of fiber optic sensors in medicine are very perspective.

Deuterium as a cleaning gas for ITER first mirrors: experimental study on beryllium deposits from laboratory and JET-ILW

Cleaning techniques for metallic first mirrors are needed in more than 20 optical diagnostic systems from ITER to avoid reflectivity losses. Plasma sputtering is considered as one of the most promising techniques to remove deposits coming from the main wall (mainly beryllium and tungsten). Previous plasma cleaning studies were conducted on mirrors contaminated with beryllium and tungsten where argon and/or helium were employed as process gas, demonstrating removal of contamination and recovery of optical properties. Still, both above-mentioned process gases have a non-negligible sputtering yield on mirrors. In this work, we explored the possibility to use a sputter gas having a small impact on mirrors while being efficient on Be deposits, e.g. deuterium. Two sputtering regimes were studied, on laboratory deposits as well as on mirrors exposed in JET-ILW, namely physical sputtering (220 eV ion energy) and chemically assisted physical sputtering (60 eV ion energy) using capacitively coupled plasma with radio frequency. The removal of Be and mixed Be/W contaminants, as well as the recovery of reflectivity, was achieved when deuterium was employed at 220 eV while cleaning at 60 eV was only fully efficient on laboratory beryllium deposits. On mirrors exposed in JET-ILW, the situation is more complex due to the presence of tungsten in the contaminant film, leading to the formation of a tungsten enriched surface that is not easily sputtered, especially at 60 eV.

Optical diagnostic systems based on Shenguang III

Optical diagnostic system plays an important role in inertial confinement fusion (ICF) experiment. Some key physical quantities and parameters in fusion can be diagnosed intuitively. In this review, three typical diagnostic systems on Shengang III facility are introduced, including imaging velocity interferometer system for any reflector (VISAR), fusion-reaction diagnostic system and backscatter light diagnostic system. VISAR can be used to measure velocity of free surface or shock wave traveling history in transparent media, which is an important diagnostic technique for shock wave velocity regulation, material compression characteristics and radiation temperature measurement. The fusion reaction-history diagnostic system can be used to accurately measure the fusion rate of ICF experiment. It’s a key diagnostic technique to study implosion dynamics and understand the mixed effect. Backscatter light diagnostic system is capable to measuring the energetic quotient stimulated by laser and plasma interaction (LPI), which produce important supports for calculating the coupling efficiency of driven laser and target.

Digital holographic interferometry for cultural heritage structural diagnostics: A coherent and a low‐coherence optical set‐up for the study of a marquetry sample

AbstractCultural heritage conservation is an active field of research, where there is an ever‐growing demand for nondestructive and noninvasive diagnostic techniques, for performing remote analysis and diagnosis of the condition of historical structures and pieces of art, often of very high cultural and historical value. In this context, holographic interferometry is a very well‐established optical technique for research in cultural heritage, which brings together some very basic and critical properties such as contactless examination and nondestructivity, accuracy, repeatability, and a wide range of applicability. In this paper, the optical technique of digital holographic interferometry is tested on mock‐up, art‐related targets, with 2 different light sources, in an attempt to expand the technique towards a new approach that will profit from an easy‐to‐operate, inexpensive, and tunable source, offering a broad spectrum and wavelength selectivity, according to the needs of the experiments. Examples are presented, and the results demonstrate the effectiveness of the proposed modified experimental scheme for defect mapping, to be used in structural documentation reports, and for its exploitation in future hybrid optical diagnostic systems and data processing.

Plasma cleaning of ITER first mirrors

Nuclear fusion is an extremely attractive option for future generations to compete with the strong increase in energy consumption. Proper control of the fusion plasma is mandatory to reach the ambitious objectives set while preserving the machine’s integrity, which requests a large number of plasma diagnostic systems. Due to the large neutron flux expected in the International Thermonuclear Experimental Reactor (ITER), regular windows or fibre optics are unusable and were replaced by so-called metallic first mirrors (FMs) embedded in the neutron shielding, forming an optical labyrinth. Materials eroded from the first wall reactor through physical or chemical sputtering will migrate and will be deposited onto mirrors. Mirrors subject to net deposition will suffer from reflectivity losses due to the deposition of impurities. Cleaning systems of metallic FMs are required in more than 20 optical diagnostic systems in ITER. Plasma cleaning using radio frequency (RF) generated plasmas is currently being considered the most promising in situ cleaning technique. An update of recent results obtained with this technique will be presented. These include the demonstration of cleaning of several deposit types (beryllium, tungsten and beryllium proxy, i.e. aluminium) at 13.56 or 60 MHz as well as large scale cleaning (mirror size: 200 × 300 mm2). Tests under a strong magnetic field up to 3.5 T in laboratory and first experiments of RF plasma cleaning in EAST tokamak will also be discussed. A specific focus will be given on repetitive cleaning experiments performed on several FM material candidates.

Matlab fractal techniques used to study the structural degradation caused by alpha radiation to laser mirrors

Almost all optical diagnostic systems associated with classical particle accelerators or with new state-of-the-art particle accelerators, such as those developed within the European Collaboration ELI-NP (Extreme Light Infrastructure-Nuclear Physics) (involving extreme power laser beams), contain in their infrastructure high quality laser mirrors, used for their reflectivity and/or their partial transmittance. These high quality mirrors facilitate the extraction and handling of optical signals. When optical mirrors are exposed to high energy ionizing radiation fields, their optical and structural properties will change over time and their functionality will be affected, meaning that they will provide imprecise information. In some experiments, being exposed to mixed laser and accelerated particle beams, the deterioration of laser mirrors is even more acute, since the destruction mechanisms of both types of beams are cumulated. The main task of the work described in this paper was to find a novel specific method to analyse and highlight such degradation processes. By using complex fractal techniques integrated in a MATLAB code, the effects induced by alpha radiation to laser mirrors were studied. The fractal analysis technique represents an alternative approach to the classical Euclidean one. It can be applied for the characterization of the defects occurred in mirrors structure due to their exposure to high energy alpha particle beams. The proposed method may be further integrated into mirrors manufacturing process, as a testing instrument, to obtain better quality mirrors (enhanced resistance to high energy ionizing beams) by using different types of reflective coating materials and different deposition techniques. Moreover, the effect of high energy alpha ionizing particles on the optical properties of the exposed laser mirrors was studied by using spectrophotometric techniques.

Repetitive cleaning of a stainless steel first mirror using radio frequency plasma

First mirrors (FMs) are crucial components of optical diagnostic systems in present-day tokamaks and future fusion reactors. Their lifetimes should be extremely limited due to their proximity to burning plasma, greatly influencing the safe operation of corresponding diagnostics. Repetitive cleaning is expected to provide a solution to the frequent replacement of contaminated FMs, thus prolonging their lifetimes. Three repetitive cleaning cycles using radio frequency plasma were applied to stainless steel (SS) FM samples, to evaluate the change of the mirrors’ optical properties and morphology during each cycle. Amorphous carbon films were deposited on mirror surfaces under identical conditions in three cycles. In three cycles with identical cleaning parameters, the total reflectivity was restored at up to 95%. Nevertheless, with successive cleaning cycles, the FM surfaces gradually appeared to roughen due to damage to the grain boundaries. Correspondingly, the diffuse reflectivity increased from a few percent to 20% and 27% after the second and third cycles. After optimizing the cleaning parameters of the second and third cycles, the roughness showed a significant decrease, and simultaneously the increase of diffuse reflectivity was remarkably improved.

Engineering design and analysis of an ITER-like first mirror test assembly on JET

The ITER first mirrors are the components of optical diagnostic systems closest to the plasma. Deposition may build up on the surfaces of the mirror affecting their ability to fulfil their function. However, physics modelling of this layer growth is fraught with uncertainty. A new experiment is underway on JET, under contract to ITER, with primary objective to test if, under realistic plasma and wall material conditions and with ITER-like first mirror aperture geometry, deposits do grow on first mirrors. This paper describes the engineering design and analysis of this mirror test assembly.The assembly was installed in the 2014–15 shutdown and will be removed in the 2016–17 shutdown.

Optical diagnostics of selective laser melting and monitoring of single-track formation

The article presents the optical diagnostics results of the selective laser melting process of single-track production. The track defects detection (such as balling effect, powder free zone formation, sparking) was shown, as well as the visualization of the independent particles consolidation in a solid track. The metal evaporation and the formation of the melt pool specific gas dynamic conditions were considered as important physical phenomena. The velocities of the particle emission from the melt pool, the rate of their involvement, and the velocity of the gas flow were estimated. The results make it possible to evaluate the kinetics of mass transfer under selective laser melting process. The surface thermal field of the laser-irradiated zone strongly influences the material qualitative characteristics after selective laser melting. The results becomes the basis for the development of optical monitoring and diagnostic systems for laser additive manufacturing processes based on the melt pool temperature online controlling.

Low-Coherence Reflectometry for Refractive Index Measurements of Cells in Micro-Capillaries.

The refractive index of cells provides insights into their composition, organization and function. Moreover, a good knowledge of the cell refractive index would allow an improvement of optical cytometric and diagnostic systems. Although interferometric techniques undoubtedly represent a good solution for quantifying optical path variation, obtaining the refractive index of a population of cells non-invasively remains challenging because of the variability in the geometrical thickness of the sample. In this paper, we demonstrate the use of infrared low-coherence reflectometry for non-invasively quantifying the average refractive index of cell populations gently confined in rectangular glass micro-capillaries. A suspension of human red blood cells in plasma is tested as a reference. As a use example, we apply this technique to estimate the average refractive index of cell populations belonging to epithelial and hematological families.

Overview: Development of the National Ignition Facility and the Transition to a User Facility for the Ignition Campaign and High Energy Density Scientific Research

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory has been operational since March 2009 and has been transitioning to a user facility supporting ignition science, high energy density stockpile science, national security applications, and fundamental science. The facility has achieved its design goal of 1.8 MJ and 500 TW of 3ω light on target, and has performed target experiments with 1.9 MJ at peak powers of 410 TW. The National Ignition Campaign (NIC), established by the U.S. National Nuclear Security Administration in 2005, was responsible for transitioning NIF from a construction project to a national user facility. Besides the operation and optimization of the use of the NIF laser, the NIC program was responsible for developing capabilities including target fabrication facilities; cryogenic layering capabilities; over 60 optical, X-ray, and nuclear diagnostic systems; experimental platforms; and a wide range of other NIF facility infrastructure. This paper provides a summary of some of the key experimental results for NIF to date, an overview of the NIF facility capabilities, and the challenges that were met in achieving these capabilities. They are covered in more detail in the papers that follow.

Plasma cleaning of beryllium coated mirrors

Cleaning systems of metallic first mirrors are needed in more than 20 optical diagnostic systems from ITER to avoid reflectivity losses. Currently, plasma sputtering is considered as one of the most promising techniques to remove deposits coming from the main wall (mainly beryllium and tungsten). This work presents the results of plasma cleaning of rhodium and molybdenum mirrors exposed in JET-ILW and contaminated with typical tokamak elements (including beryllium and tungsten). Using radio frequency (13.56 MHz) argon or helium plasma, the removal of mixed layers was demonstrated and mirror reflectivity improved towards initial values. The cleaning was evaluated by performing reflectivity measurements, scanning electron microscopy, x-ray photoelectron spectroscopy and ion beam analysis.