Wahyu Setia Budi

Shock Excitation and Cooling Stage in the Laser Plasma Induced by a Q-Switched Nd:YAG Laser at Low Pressures

An experimental study has been carried out on the dynamical process taking place in the secondary plasma generated by a Q-switched Nd:YAG laser (80 mJ, 8 ns) on a copper target at reduced pressure. Accurate dynamical characterization of the cross-sectional view of the plasma has been made possible by the unique combination of a plasma confinement configuration and the time-resolved measurement technique. In addition to reaffirming the role of the blast-wave mechanism in the generation of secondary plasma, an analysis of the time-resolved spatial distributions of emission intensities and the time-resolved spatial distributions of temperature was made. As a result, the occurrence of two-stage emission processes, the “shock excitation stage” and “cooling stage,” has been proved. For instance, at 2 Torr it is shown that the emission process is initiated by a brief shock excitation process (∼ 1 μs) and followed by a longer cooling process (∼ 3 μs). The experimental results concerning the characteristics of the plasma can be well understood by considering the two-stage processes.

Neutral and Ionic Emission in Q-Switched Nd:YAG Laser-Induced Shock Wave Plasma

Excitation mechanisms for copper and zinc atoms as well as their ionic species in the Q-switched (Q-sw) Nd:YAG laser-induced shock wave plasma have been investigated with a time-gated optical multichannel analyzer (OMA) system for various experimental conditions. It is demonstrated that the shock excitation process is the main mechanism responsible for the emission spectra for laser energy ranging from 8 to 86 mJ and surrounding air pressure from 2 to 50 Torr. At air pressure below 2 Torr, collision-induced excitation appears to take over and becomes the operative mechanism. In all cases, the neutral emission dominates over the ionic emission, leading to a high signal-to-background ratio, which tends to decrease, however, at higher laser energy and air pressure.

Design of crack detection system for concrete built infrastructure based on fiber optic sensors

This paper presents crack detection in concrete built infrastructure using fiber optic sensors based on the pressure measurement system. Fiber optic sensors in this experimental study were constructed using micro-bending techniques. The bends in optical fiber were evaluated based on pressures given by Compression Testing Machine (CTM). Pressure was performed on the surface of concrete specimens, in which there was a fiber optic in the middle of each specimen. Dimension of concrete specimen was 15 cm x 10 cm, with thickness variations of 2cm, 4cm and 6cm. The results showed that the higher the pressure value, the lower the intensity of signal light in optical fiber. It is mentioned as the attenuation of fiber optic. It depends on the thickness and the maximum strength of the specimen.This paper presents crack detection in concrete built infrastructure using fiber optic sensors based on the pressure measurement system. Fiber optic sensors in this experimental study were constructed using micro-bending techniques. The bends in optical fiber were evaluated based on pressures given by Compression Testing Machine (CTM). Pressure was performed on the surface of concrete specimens, in which there was a fiber optic in the middle of each specimen. Dimension of concrete specimen was 15 cm x 10 cm, with thickness variations of 2cm, 4cm and 6cm. The results showed that the higher the pressure value, the lower the intensity of signal light in optical fiber. It is mentioned as the attenuation of fiber optic. It depends on the thickness and the maximum strength of the specimen.

Pulsed CO2 laser-induced gas plasma spectroscopy based on single beam splitting for trace metal analysis on a material surface

ABSTRACT Laser-induced gas plasma spectroscopy based on pulsed CO2 laser beam splitting has been applied to the problem of trace film analysis on the silicon surface. In this study, 2.1 J of laser energy (70% of the laser beam) was focused at a 10-degree incidence on a metal mesh attached to a sample surface containing trace metal elements in order to produce a gas plasma. The remaining part of the laser beam (approximately 30% or 0.9 J) was employed to vaporize a film which had been deposited on the material by focusing the laser beam 3 cm under the surface. In this scheme, the vaporized metal film moves into the gas plasma region, in which the dissociation and excitation takes place. Our measurements show that the detection of Cr on the silicon surface can be made with high sensitivity. The limit of detection of Cr in the silicon material was approximately 7.5 × 1012 atom/cm2.

An algorithm for automated modulation transfer function measurement using an edge of a PMMA phantom: Impact of field of view on spatial resolution of CT images

Abstract Purpose The purpose of this study was to introduce a new algorithm for automated measurement of the modulation transfer function (MTF) using an edge of a readily available phantom and to evaluate the effect of reconstruction filter and field of view (FOV) on the spatial resolution in the CT images. Methods Our automated MTF measurement consisted of several steps. The center of the image was established and an appropriate region of interest (ROI) designated. The edge spread function (ESF) was determined, and a suitably interpolated ESF curve was differentiated to obtain the line spread function (LSF). The LSF was Fourier transformed to obtain the MTF. All these steps were accomplished automatically without user intervention. The results of the automated MTF from the edge phantom were validated by comparing them with a point image, and the results of the automated calculation were validated by the standard fitting method. The automated MTF calculation was then applied to the images of two polymethyl methacrylate (PMMA) phantoms and a wire phantom which had been scanned by a Toshiba Alexion 4‐slice CT scanner and reconstructed with various filter types and FOVs. Results The difference in the 50% MTF values obtained from the edge and point phantoms were within ±4%. The values from the automated and fitted methods agreed to within ±2%, indicating that the automated MTF calculation was accurate. The automated MTF calculation was able to differentiate MTF curves for various filters. The spatial resolution values were 0.37 ± 0.00, 0.71 ± 0.01, and 0.78 ± 0.01 cycles/mm for FC13, FC30 and FC52 filters, respectively. The spatial resolution of the images decrease linearly (R 2 > 0.98) with increasing FOVs. Conclusion An automated MTF method was successfully developed using an edge phantom, the PMMA phantom. The method is easy to implement in a clinical environment and is not influenced by user experience.

Synthesis and characterization of high-purity gold nanoparticles by laser ablation method using low-energy Nd:YAG laser 1064 nm

High-purity gold nanoparticles (GNPs) has been successfully synthesized by using laser ablation method utilizing low-power neodymium yttrium aluminum garnet (Nd:YAG) laser at the fundamental wavelength. Experimentally, pulse laser beam (Nd:YAG laser, 1064 nm, 7 ns, 30 mJ) was directed and focused onto a high-purity gold sheet (99.95%), which was placed into a pure liquid of deionized water, to produce GNPs colloid. Dark-red color colloid of high-purity GNPs was successfully synthesized. The GNPs had a spherical shape with an average diameter of 23.5 nm and standard deviation of 6.4 nm. The surface plasma resonance was centered at wavelength maximum at 520 nm.

The impacts of multiple lightshelves on natural lighting distribution and effective temperature at office rooms

Daylighting with light-shelf is not a simple strategy. Therefore, this research aims to investigate how far the application of light-shelf can block direct sunlight and how much the distribution of daylight at office rooms is produced. This research is a simulation using EnergyPlus from OpenStudio. Data as measurement results collected from on-site research were used as the validation base of the simulations both with multiple light shelves and without multiple light shelves. The building orientation is toward north east (azimuth 51°), and the result showed that using multiple light shelves on the building was able to distribute evenly the intensity of natural lighting into the rooms. On the edge of the windows, there has been change of the light intensity which was previously too bright (from 925 Lux at 5 p.m. for the lowest and 7200 Lux at 9 a.m. for the highest; to 460 Lux at 5 p.m. for the lowest and 1400 Lux at 12.00 p.m. for the highest). Besides, the use of multiple light shelves was also able to lower the room temperature particularly at rush hours starting from 9.00 a.m. to 3.00 p.m. where the biggest difference of the temperature occurred at 3.00 p.m. (between 29.1 °C and 28.4 °C in which the temperature decreased 0.7 °C). These aforementioned facts have given contribution to the efficiency of energy used in AC while the main benefit of this research is developing knowledge about daylighting in architectural design particularly in passive design method.

EFFECT of VARIATION of C-ARM ANGLE POSITION to DOSE RATE was RECEIVED in SURGICAL PROCEDURE at the CENTRAL SURGICAL INSTALLATION

An anthropomorphic phantom dose rate measurement has been done in C-Arm room at Central Surgical Installation with surveymeter. Measurements were made with 8 variations of the C-Arm fluoroscopy angle commonly used in the operating procedure, as well as the 1 meter point of measurement against the radiation source. The variations of these angles are 00, 450, 900, 1350, 1800, 2250, 2700, and 3150. The dose rate measurements at a distance of 1 m from the radiation source with angle variations are 380 μSv/h, 430 μSv/h, 680 μSv/h, 29 μSv/h, 220 μSv/h, 350 μSv/h, 1370 μSv/h and 1020 μSv/h. The measurement results showed that the highest dose rate at the C-arm angle of 2700 and the lowest dose at the C-Arm 1350 angle position. From the measurement results can be seen the effect of angular position used with the acceptable dose rate, the lowest to highest dose rate received based on the angular position in sequence are 1350, 1800, 2250, 00, 450, 900, 3150, 2700. Keywords— C-Arm, Laju dosis, Fluoroskopi, Phantom Antropomorfik, Titik pengukuran

Rapid Detection of Oil Pollution in Soil by Using Laser-Induced Breakdown Spectroscopy

Detection of oil pollution in soil has been carried out using laser-induced breakdown spectroscopy (LIBS). A pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (1,064 nm, 8 ns, 200 mJ) was focused onto pelletized soil samples. Emission spectra were obtained from oil-contaminated soil and clean soil. The contaminated soil had almost the same spectrum profile as the clean soil and contained the same major and minor elements. However, a C–H molecular band was clearly detected in the oil-contaminated soil, while no C–H band was detected in the clean soil. Linear calibration curve of the C–H molecular band was successfully made by using a soil sample containing various concentrations of oil. The limit of detection of the C–H band in the soil sample was 0.001 mL/g. Furthermore, the emission spectrum of the contaminated soil clearly displayed titanium (Ti) lines, which were not detected in the clean soil. The existence of the C–H band and Ti lines in oil-contaminated soil can be used to clearly distinguish contaminated soil from clean soil. For comparison, the emission spectra of contaminated and clean soil were also obtained using scanning electron microscope-energy dispersive X-ray (SEM/EDX) spectroscopy, showing that the spectra obtained using LIBS are much better than using SEM/EDX, as indicated by the signal to noise ratio (S/N ratio).