Satoshi Ikezawa

Detection of Cesium from Pollucite Using Laser-Induced Breakdown Spectroscopy

The purpose of this research is to detect the atomic spectrum of cesium using laser-induced breakdown spectroscopy (LIBS). In this study, pollucite ((Cs,Na)(AlSi2)O6.nH2O) was used as a test sample for the LIBS measurement. LIBS is a useful tool for the determination of the elemental composition of various materials and it does not require any preprocessing step. The Nd:YAG laser was operated at 1064 nm to generate a 50-mJ Q-switched pulse with a width of 8 ns (full width at half maximum, FWHM). The breakdown emissions were dispersed by a grating with a groove density of 1200 lines/mm and the resulting electrical signal was recorded using a streak camera. The plasma intensity was optimized with respect to the background. Spectral measurements were carried out after an appropriate delay time to allow for the decay of the continuum radiation. In the experiments, 100 laser shots were used to record data for each spectrum in ambient air. The results of the experiments showed that the atomic signals corresponding to pollucite were obtained easily by LIBS measurements. Thus, spectrum peaks due to cesium, sodium, aluminum, and silicon are observed. In particular, the characteristics of the cesium spectrum play an important role in establishing the LIBS system for environmental monitoring, which may be used to detect radioactive elements emitted from nuclear plants.

Fabrication of Two Different Probe Architectures for Ultra-Compact Image Sensors for Root Canal Observations

With the development of dental instruments, such as dental microscopes and cone beam computed tomography, the precision of current dental diagnosis and treatment has greatly improved. However, the observation of deep periodontal pockets, fractures near the root apex, and collaterals of root canals is difficult using these instruments. To solve these problems, we developed two types of micro-image sensors that can be used for the observation of root canals. The first image sensor is an external-irradiation probe that uses an external light source. This probe has high resolution and a wide field of view. The other sensor is an internal-irradiation probe, which can be used to observe an image and transmit the illumination light with a single probe. The external-irradiation probe has an image fiber with a diameter of 600 μm and a gradient index (GRIN) lens. The internal-irradiation probe has an image fiber with a diameter of 300 μm, a GRIN lens, and 40 optical fibers with a diameter of 40 μm each as a light source. Using these probes, we captured the image of a resolution chart; line spaces with the widths of 10-100 μm were observed using both types of probes. The evaluations of the visibility of the captured image showed higher measurement values than those of commercially available endoscopes. We will apply this ultra-compact image sensor to various fields besides dentistry, such as medical and industrial applications.

Multi-spectral Analytical Systems Using LIBS and LII Techniques

In this paper, we propose an advanced approach to particle analysis, involving laser-induced breakdown spectroscopy (LIBS) and laser-induced incandescence (LII) temporal analytical techniques. Various technical properties of fine particles are analyzed via LIBS and LII. LIBS is a useful tool for determining the elemental composition and relative concentration of various materials, whereas LII facilitates the measurement of particle size. Both techniques do not require any pre-processing. The combined use of the LIBS and LII techniques enables highly synergistic fine particle measurement. In the LIBS section, we propose spectrometric analysis via a novel ink-jet technique, and we discuss the effectiveness of Ar as a surrounding gas. In the LII section, we compare the calculated particle size prediction with the experimental results.

A novel method for evaluating triaxial strain gages used in printed circuit board assemblies (PCBA) strain monitoring

This paper reports a novel method for evaluating strain gages. In this method, the evaluated gage is attached at a specific location of coupon board, and then deflects 5 known distances by steps by the insertion of shims with different thicknesses. The strain for each bended status is recorded and can be compared against expected variation. If the principle strain values and corresponding angles within the tolerance, the gage passes the test and can be applied in practical strain measurement with increased confidence, otherwise it will be deprived of the qualification to accept. Moreover, this method combines with accredited gages can also be used to find and eliminate many errors due to gage placement, gage attachment, measurement equipment setup, and lead wires. In order to prove the validity of the given method, three types of gages from various suppliers at are evaluated, and the results of test broadly consistent with technical backgrounds of their respective manufacturers.

Development of cesium detection system using laser-induced breakdown spectroscopy

This report presents a new cesium sensing method that uses laser-induced breakdown spectroscopy (LIBS). Conventionally, beta rays and germanium semiconductor detectors have been used for Cs-137 analysis. These methods typically require laboratory-scale analytical facilities. On the other hand, LIBS allows for direct elemental composition measurement of samples regardless of their physical state without preprocessing or laboratory facilities. Even if it is nearly impossible to separate isotopic data from the spectrum of an LIBS measurement, measurement of cesium levels is important for investigating the causes of abnormal radiation levels because the abundance of cesium is low under normal conditions. We report on cesium spectra results as measured by LIBS; the measurements were of sufficient resolution to obtain quantitative information for calculating the expected quantity of radioactive cesium from the isotope ratios.

Real scene capturing using spherical single-element lens camera and improved restoration algorithm for radially variant blur

A camera module employing spherical single-element lens imaging system (SSLIS) is introduced in this study. This type of imaging system can be used in compact digital cameras or mobile phone cameras, and it provides the advantages of simple design, reduced device bulkiness, and reduced manufacturing costs. When compared with conventional camera modules, our system produces radially variant blurred images, which can be satisfactorily restored by means of a polar domain deconvolution algorithm proposed in our previous study. In this study, we demonstrate an improved version of this algorithm that enables full-field-of-view (FOV) image restoration instead of the partial FOV restoration obtained via our previous algorithm. This improvement is realized by interpolating the upper and arc-shaped boundaries of the panoramic polar image such that the ringing artifacts around the center and four boundaries of the restored Cartesian image are greatly suppressed. The effectiveness of the improved algorithm is verified by image restoration of both computer simulated images and real-world scenes captured by the spherical single lens camera module. The quality of the restored image depends on the overall sparsity of all the point spread function (PSF) block Toeplitz with circulant blocks (BTCB) matrices used to restore a radially blurred image.

Sensing system for quantitative analysis of metal particles using laser-induced breakdown spectroscopy

This report describes a real-time sensing system for the detection and analysis of fine metal particles using laser-induced breakdown spectroscopy (LIBS). In conventional particle measurement methods, the scanning mobility particle sizer (SMPS) is widely used to obtain particle size distributions. However, when more details on particles are required, another chemical analysis must be performed separately from the one involving the SMPS. Hence, it is difficult to obtain the size and composition of fine particles in real time by conventional methods. By the proposed LIBS method, it is possible to obtain information on the density of fine particles as well as the chemical components of even ultrafine particles. Metal particles are focused on because the use of metal nanoparticles is expanding with emerging micro- and nanotechnologies. This work describes the use of the LIBS system as a fine metal particle monitoring system in a fabrication process using nanometal materials.

Development of sensing system for carbonaceous particles using LIBS combined with LII temporal analytical technique

This report describes a new sensing system for carbonaceous particles detection using combination with two techniques of laser-induced breakdown spectroscopy (LIBS) and laser-induced incandescence (LII). Our research group has improved LIBS system applied for quantitative analysis. Although the basic principal of the LIBS quantitative measurements were well understood, several uncertainties still remained for complete description especially for the particle size measurement. Elemental composition and density of the particle were determined by using LIBS. Particle size measurement was accomplished with the help of LII. On the presented system, only controlling the power density of the light source allowed to switch from LIBS to LII.

Control of a Micro-Droplet for Laser-induced Breakdown Spectroscopy Solution Measurement

In this paper, laser-induced breakdown spectroscopy (LIBS) using micro-droplet NaCl solution and set-up for control of micro-droplets are described. Micro-droplets controlling technique is important for solution quantitative analysis. In this study, micro-droplet ejection system for sampling is designed and presented. This micro-droplet ejection system enable a constant volume of the sample liquid to be obtained and it takes advantage of the liquid physical state; the density of the solution can be controlled accurately. The method presented here generates small droplets (diameter 30 μm) by confining the entire volume of the sample material in the laser beam spot area (minimum beam spot diameter: 53.2 μm) and separating it from its surroundings. Using this liquid micronizing method, improved sensitivities are obtained. The Advantage of LIBS is a useful method for determining the elemental composition of various materials regardless of their physical state (solid, liquid, or gas) and without any preprocessing; it is a type of atomic emission spectroscopy (AES). Despite the advantage of qualitative analysis, quantitative analysis is difficult because of sample and plasma fluctuations. Generating constant volume of micro-size sample and proper sample control technique contribute to LIBS quantitative analysis.

Development of an Image Sensor for Dentistry - Fiber Connecting Technique with the Gradient Index (GRIN) Rod Lens

In dentistry, endodontic treatment becomes necessary when dental caries progresses deep into the tooth and reaches the dental pulp or the periapical tissue. A large part of this treatment is performed without direct observation of the root canals. Previously, we reported a prototype of a dental endoscope. In this study, we attempted to develop a novel image sensor for dental endodontic diagnosis and treatment that allows capturing an image of the fine constructions inside the root canals.　Our fabricated probe contains an image fiber, a GRIN lens, and optical fibers as light sources. These materials are encased inside a stainless steel tube to ensure the durability. In previous experiments, we attempted to connect all materials in one step. However, the captured images had deviations along the center axis between the image fiber and GRIN lens. To solve this problem, we considered a new, two-step method for connecting the two materials. In this method, an image fiber and a GRIN lens with the same diameter were placed on stages capable of three-dimensional fine positional adjustments at a resolution of 0.01 mm. The surfaces of the materials were connected under observation through a microscope. An evaluation of the captured images showed that the deviations in the previous images were 22.4 μm along the X-axis and 45.7 μm along the Y-axis. In contrast, the deviations with the new method were 16.7 μm and 8.9 μm along the X-axis and Y-axis, respectively. Therefore, the new method greatly improved precision along each axis. With this method, our fabricated probe could capture and evaluate images more efficiently. We are now trying to fabricate and evaluate a new image sensor.