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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - In vivo and online temperature monitoring based on fiber Bragg greatings during tumor treatment with nanosecond pulse electric field
摘要： the clinical practice, a compact, in-vivo and online monitoring scheme is an important requirement. A fiber Bragg grating (FBG) sensing system was used to online monitor the temperature at the surface of / inside the liver tissue of a rabbit under nanosecond pulse electric field (nsPEF). Single point measurement between the electrodes and multi-point measurement surrounding one electrode were both carried out. Experimental results show that, due to equally spaced (Δt=0.5 s) 300 ns-pulses with E=20 kV/cm at a repetition rate of 4 Hz, the temperature rise in the rabbit liver tumor usually does not exceed ΔΤ=6℃ for 300 pulses. Theoretical analysis of Joule heating model fits well with the experimental results. Both direct measurements and theoretical modelling demonstrated that nsPEF could not deliver enough energy to heat the treated tissue significantly, thus a hyperthermic effect on the tissue can be excluded during this kind of treatment with much high electric field strength and extremely short duration.
关键词： Fiber Bragg grating,Nanosecond pulse electric field,In-vivo temperature monitoring
更新于2025-09-16 10:30:52
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Laser Ablation - From Fundamentals to Applications || Nanosecond Laser Ablation: Mathematical Models, Computational Algorithms, Modeling
摘要： The basic mathematical models, computational algorithms, and results of mathematical modeling of various modes of laser action on metals are considered. It is shown that for mathematical description and analysis of the processes of laser heating, melting, and evaporation of condensed media, various theoretical approaches are used: continuum, kinetic, atomistic, etc. Each of them has its own field of applicability, its advantages, and disadvantages. Mathematical description of ns-laser ablation is usually carried out within the framework of continuum approach in the form of hydrodynamic models that take into account reaction of irradiated material to varying density, pressure, and energy both in the target and in the vapor-gas medium. Within the framework of continuum approach, a multiphase, multifront hydrodynamic model and computational algorithm were constructed that were designed for modeling ns-PLA of metal targets embedded in gaseous media. It is shown that proposed model and computational algorithm allow to carry out the simulation of interrelated mechanisms of heterogeneous and homogeneous evaporation of metals manifested as a series of explosive boiling. Modeling has shown that explosive boiling in metals occurs due to the presence of a near-surface temperature maximum. It has been established that in ns-PLA, exposure regimes can be realized in which a phase explosion is the main mechanism of material removal. The verification of reliability of obtained results was carried out by comparing experimental data and calculations with atomistic models.
关键词： explosive boiling,phase explosion,hydrodynamic model,laser action,nanosecond pulse,mathematical modeling,subsurface temperature maximum
更新于2025-09-12 10:27:22
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Correlation between defect absorption and nano-second laser-induced damage of HfO2/SiO2 based high reflective coatings at 1064?nm
摘要： The distribution of defect weak absorption and nanosecond pulse laser induced damage characteristics of HfO2/SiO2 multilayers were investigated. A combination of in-situ measurements of defect weak absorption distribution and laser induced damage threshold (LIDT) map was proposed, whereby the evolution of defect weak absorption and the laser induced damage morphology under laser irradiation was studied. During the laser irradiation, some nodular and scalded defects can be removed or passivated by the low flux laser, and the absorption of these defect types was reduced accordingly. Besides, catastrophic destruction defects with enhanced absorption after laser irradiation would develop into catastrophic damage. Further, two-dimensional scanning of the sample surface was used to study the relationship between defects weak absorption and the LIDT. The results indicated that the correlation of defects weak absorption intensity distribution and LIDT map depended on defect evaluation properties during the laser irradiation.
关键词： Nanosecond pulse laser,HfO2/SiO2 multilayers,High reflective coatings,Laser-induced damage,Defect absorption
更新于2025-09-11 14:15:04
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Semiconductor opening switch generator with a primary thyristor switch triggered in impact-ionization wave mode
摘要： The results of the investigation involving a thyristor switch triggered in the impact ionization wave mode are presented. This switch is intended for operation as a primary switch in a nanosecond pulse generator with a semiconductor opening switch (SOS). The thyristor switch is based on commercial low-frequency tablet thyristors stacked in a joint assembly of up to 6 pieces connected in series. At a charging voltage of 2–12 kV and switching energy of up to 16 J, the switch operates with a discharge current of up to 8 kA, a current rise rate in the range from 14 to 54 kA/μs, and a switching ef?ciency of ～0.9. It is shown that an increase in a voltage rise rate on thyristors at the triggering stage reduces energy loss in the thyristor switch during the current ?ow. The SOS pumping circuit contains one magnetic element—a pulse transformer, which simpli?es the generator and increases its ef?ciency. The SOS generator has an output voltage of up to 300 kV and a peak power of up to 250 MW with a pulse duration of ～50 ns. The thyristor switch in the generator operates at a voltage of 12 kV and provides current ?ow with the amplitude of up to 7.5 kA with a duration of ～500 ns and a current rise rate of ～54 kA/μs. The pulse repetition frequency of the generator is 1 kHz in the burst mode of operation.
关键词： semiconductor opening switch,nanosecond pulse generator,thyristor switch,impact ionization wave
更新于2025-09-10 09:29:36