Sharif Digital Repository

The luminescence parameters of laser-induced bubble in the presence of an acoustic field in water are studied. A comparison is made between parameters such as bubble radius, interior temperature, and pressure of the bubble induced by laser and an acoustic field influenced by different driving pressure amplitudes. It is found that the bubble volume induced by laser at the collapse instant is more than 106 times larger than the one induced by an acoustic field. It is also noticed, by increasing the driving pressure amplitude, the bubble radius decreases in both cases, however, the bubble interior pressure and temperature increase  

This paper describes a double-cell method, which offers some advantages in image capturing and analysis of the planar laser-induced fluorescence (PLIF) experiments. Double static-cell and circulating-static designs are tested and the fluorescence results are reported. The static-static design offers some advantages when comparing the fluorescence signals for two different dyes, the effect of additives, and of oxidation, whereas the circulating-static design provides an effective method to study the thermal contributions of the measured signal, the photostability of a particular dye, the effect of adding agents, and the quenching effects on a dye under study. In this experiment Rhodamine-WT... 

The Possibility of the laser assisted sonofusion is studied via single bubble sonoluminescence (SBSL) in Deuterated acetone (C3D6O) using quasi-adiabatic and hydro-chemical simulations at the ambient temperatures of 0 and -28.5 °C. The interior temperature of the produced bubbles in Deuterated acetone is 1.6 × 106 K in hydro-chemical model and it is reached up to 1.9 × 106 K in the laser induced SBSL bubbles. Under these circumstances, temperature up to 107 K can be produced in the center of the bubble in which the thermonuclear D-D fusion reactions are promising under the controlled conditions. © 2016 Author(s)  

By using the planar laser induced florescence experiment (PLIF), a resorufin (RSRF) dye solution was tested as an oxygen probe. The photoreaction of RSRF dye was investigated and the oxidation process of this fluorescent probe molecule was demonstrated. The effect of the oxygen bubbles on tracing dissolved oxygen was also investigated in this study. Results obtained for this sensitive molecular probe dye are very interesting and verify that such an agent can be used effectively for investigating different interesting phenomena affecting the fluorescence. The temporal and spatial behaviors of the oxidation and fluorescence processes were described in this report. For a delay time of 4500 ms... 

The goal of this paper is to describe essential criteria for image analysis of planar laser-induced fluorescence (PLIF) signals. A new image file conversion method is introduced and some typical illustrative examples showing the potential applications of the method in PLIF experiments are presented. Analysis of row, column, and total pixel counts, and the dark noise related to an image are discussed. Image segmentation, averaging and background correction can be easily done by the reported method. In our analysis it is straightforward to inspect the pixel counts and check for saturation of the camera sensors. It is also feasible to obtain a particular row or column for interpretation and it... 

Propagation of a chirped laser pulse with a circular polarization through an uprising plasma density profile is studied by using 1D-3V particle-in-cell simulation. The laser penetration depth is increased in an overdense plasma compared to an unchirped pulse. The induced transparency due to the laser frequency chirp results in an enhanced heating of hot electrons as well as increased maximum longitudinal electrostatic field at the back side of the solid target, which is very essential in target normal sheath acceleration regime of proton acceleration. For an applied chirp parameter between 0.008 and 0.01, the maximum amount of the electrostatic field is improved by a factor of 2.... 

Contamination of pistachio nuts with aflatoxin is one of the most significant issues related to pistachio health and expert. A fast pistachio aflatoxin concentration measurement method based on the laser induced fluorescence spectroscopy (LIFS) is proposed. The proposed method from theoretical and experimental points of view is analyzed. In our experiments XeCl Excimer laser is employed as an Ultra Violet (UV) source (λ=308 nm) and a UV-visible (UV-vis) spectrometer is used for fluorescent emission detection. Our setup is employed to measure the concentration of different type of Aflatoxins in pistachio nuts. Measurements results obtained by the LIFS method are compared with those are... 

Laser induced breakdown spectroscopy and subsequent acoustic response during microplasma formation are employed to identify cancerous human breast tissues. The characteristic optical emissions identify Ca, Na, and Mg rich species in cancerous tissues compared to those of healthy ones. Furthermore, we show that the characteristic parameters of the microplasma, generated on the unhealthy tissues, are elevated. We report higher decibel audio signals emanating from laser induced microplasma and a subsequent audio blueshift for malignant tissues. The higher abundance of trace elements in cancerous tissues as well as higher plasma temperature and electron density in laser induced microplasma... 

The lasing mechanism and temporal output profile of distributed feedback dye lasers is investigated, using a model based on induced polarization in the dye solution, where a more accurate behavior of the laser output is predicted. It is found that the temporal output profile of the laser is mostly determined by the concentration of dye solution and the lifetime of the upper laser level of dye molecules. To a large extent, the results of this work agree with experimental studies, even at high-level pump intensities where the self Q-switched model fails to be applied. Especially, the experimentally observed irregular intensity profile of laser output is explained. It is also shown that, when... 

In this study, simultaneous particle image velocimetry and planar laser induced fluorescence of hydroxyl radical, chemiluminescence imaging, and hot-wire measurements are utilized to study reacting low swirl flow dynamics under low to high amplitude acoustic excitations. Results show that a temporal weak recirculation zone exists downstream of the flame, which is enlarged in size under acoustic excitations. Investigations show that temporal behaviors of this recirculation zone play a significant role in flame movements and instabilities. As the acoustic wave amplitude increases, the flame lift-off distance changes drastically, resulting in flame instabilities (flashback and blowout) during... 

Gold nanoparticles are widely used as high efficient photon-thermal energy converters in a broad range of applications. This paper presents a theoretical investigation on using the optothermal properties of gold nanoparticle arrays to generate nanoscale molten and rubbery regions on the surface of an amorphous polymeric film. Nanoparticles are assumed to be embedded in a transparent silica layer and illuminated with a 7.5 ns pulsed laser at 532 nm. Simulation results are presented for systems with single gold nanoparticles, dimers and chains. Both electromagnetic and thermal interaction between nanoparticles are found to be important factors in determining the result of surface processing.... 

Relativistic electrons, generated in the interaction of an ultra-intense laser pulse with plasma in front of a high-Z solid target, when passing near the nuclei of the solid target produce several MeV highly collimated Bremsstrahlung gamma beam, which can be used to induce photo-nuclear reactions. In this work the possibility of photo-induced transmutation (γn) of a nuclear waste of 126Sn with a half-life of 100,000 years into 125Sn with a half-life of 9.64 days was investigated for the first time. Calculations based on the available experimental data show that the Bremsstrahlung γ beam generated by irradiating a 2 mm thick tantalum target as a converter with 1020Wcm-2μm2 and 10 Hz table-top... 

Optothermal properties of noble metal nanoparticles can be used in a wide range of applications. This paper presents the results of a theoretical study on the utilization of laser-induced heating of a gold nanoparticle (GNP) to melt a region of a transparent material with sub-wavelength spatial resolution. The considered system consists of a 10 or 15nm diameter GNP fixed inside a silica substrate. The silica surface is covered with a thick film of the transparent polymeric or crystalline material. The heating and melting processes are studied under a 7.5ns pulsed laser illumination. Calculations are conducted under three temperature limits, on the maximum temperature of the free electrons,... 

We present in situ whole-field measurements of the temperature field using laser-induced fluorescence in a study of bottom-chilled uni-directional solidification of aqueous ammonium chloride. We utilize a two-color, two-dye, ratiometric approach to address the significant spatial and temporal variations of laser sheet intensity field due to refractive index variations caused by the evolving concentration and temperature fields. In our work we take advantage of two temperature sensitive fluorescent dyes with opposite temperature sensitivities in order to increase the overall sensitivity and temperature resolution of the measurements. The resulting temperature sensitivity (about 4% K-1) is... 

Mixing has become a challenge in micro-fluidic systems because of the low Reynolds number in micro-channels. The method which is implemented in this paper is to use freely-swimming bacteria to enhance the mixing process. Accordingly, the Serratia marcescens bacteria were used for this matter. The mixing performance of the system is quantified by measuring the diffusion rate of Rhodamine B in a particular section of a channel connected to a chamber with varying Rhodamine B concentration. The concentration of Rhodamine B was measured using the Laser Induced Fluorescence (LIF) technique. The channel is in the form of a pipe and is closed on the extending side. In this paper, it is demonstrated... 

Laser shock peening (LSP) is known as a post processing surface treatment which can improve the mechanical properties of some materials. Shock waves are generated by confining the laser-induced plasma to cause a large pressure shock wave over a significant surface area. In the present study, effects of LSP on the electrochemical corrosion and micro hardness properties of 316L stainless steel alloy were investigated by changing the laser parameters such as the laser spot size, the average number of impacts, and the laser intensity. Since laser parameters do not cover the desired region of LSP, we have to use the proper design of experiment method, in which the D-optimal design of MATLAB was... 

A warm relativistic ideal fluid theory is proposed to study the dynamics of laser-induced high amplitude longitudinal waves in rarefied plasmas. It is demonstrated that fluid equations may be closed using an adiabatic approximation in the local rest frame of the plasma fluid. It is shown that considering three-dimensional thermal fluctuations of plasma for an interacting laser pulse that is invariant in transverse directions, considerably changes the features of describing fluid equations compared to that of previously considered one-dimensional thermal-fluctuations models. For a given shape of laser pulse these equations are solved numerically and their results are compared with those...