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Effect of the spot size on ionization and degree of plasma shielding in plumes induced by irradiation of a copper target by multiple short laser pulses
摘要： The plasma plume expansion into argon background gas at atmospheric pressure induced by irradiation of a copper target with a burst of three short laser pulses at 266 nm wavelength is studied numerically for the laser spot diameters ranging from 20 μm to 500 μm. The computational model includes a thermal model of the irradiated target and a kinetic model of plume expansion. The kinetic model is implemented in the form of the direct simulation Monte Carlo method that is redesigned to account for ionization and absorption of laser radiation in the plume. The irradiation conditions are chosen to do not induce ionization and absorption during the first pulse in the burst independently of the laser spot size. During the second pulse, the ionization is initiated in the vicinity of the irradiated target behind the shock wave that is generated during that pulse and propagates through the vapor plume created by the preceding pulse. The simulations show that the degree of ionization and plasma shielding during the second and subsequent pulses strongly increases with increasing the laser spot size. It is explained by different rates of expansion between pulses in the plumes generated at various spot sizes. At a relatively small spot size, the rapid drop of density and temperature in the plume induced by the first pulse can preclude plasma ignition during the second and further pulses. These results suggest that the use of lasers with the spot sizes that are in the order of tens of micrometers can be favorable for mitigating the effect of plasma shielding in multi-pulse laser ablation when the plumes induced by individual laser pulses strongly interact with each other.
关键词： Plume expansion,Multi-pulse irradiation,Laser spot size,Laser ablation,Plasma shielding
更新于2025-09-23 15:19:57
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Selective laser ablation and patterning on Ag thin films with width and depth control
摘要： Silver (Ag) films were deposited on glass substrates by radio frequency (RF) magnetron sputtering and then ablated by a 532 nm nanosecond pulsed laser. The effects of laser fluence and defocusing amount on the width and depth of laser-ablated grooves on 100- and 600-nm-thick Ag films were systematically investigated under single- and multi-scan ablation. The results suggested that the Ag films could be successfully removed from the substrate owing to laser-induced thermoelastic force or vaporization. It was confirmed that laser fluence and defocusing amount played very important roles in controlling the width and depth of the laser-ablated grooves. In the present work, grooves with widths ranging from 53 to 196 μm and depths ranging from 56 to 196 nm were obtained on 100-nm-thick Ag films by single-scan laser ablation, and laser ablation or removal with controllable depths was realized on 600-nm-thick Ag films by adopting single- or multi-scan (i.e., scanning numbers of 1–6). Furthermore, square spiral Ag patterns were successfully obtained by single- and multi-scan laser ablation and showed good electrical conductivity in a simple circuit. This work may have great potential applications in various fields that demand width and depth control of laser ablation/removal.
关键词： Width and depth control,Laser ablation,Ag thin films,RF magnetron sputtering,Nanosecond pulsed laser
更新于2025-09-23 15:19:57
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Outcomes of Two Treatments for Uncomplicated Pilonidal Sinus Disease: Karydakis Flap Procedure and Sinus Tract Ablation Procedure Using a 1,470a??nm Diode Laser Combined With Pit Excision
摘要： Background and Objectives: An ideal treatment for pilonidal disease should feature a low recurrence rate, minimal incision, and rapid return to daily activities. We compared the outcomes of the well‐defined Karydakis technique (KT) and a combination of pit excision (PE) and sinus tract ablation using 1,470‐nm diode laser. Study Design/Materials and Methods: In this study, from January 2016 to January 2018, patients diagnosed with uncomplicated early‐stage pilonidal sinus disease were enrolled and were treated randomly, using KT (n = 28) or a PE/laser ablation technique (PE + LAT; n = 30). Results: The mean operative times were 36.4 (25–45) minutes in the KT group and 15.1 (12–20) minutes in the PE + LAT group. Postoperative Visual Analog Scale pain scores were 4.4 in the KT group and 2.1 in the PE + LAT group. The time periods to return to normal daily activities were 2.6 (1–5) days in the PE + LAT group and 12.8 (10–20) days in the KT group. The mean Likert satisfaction scores were 3.8 in the KT group and 4.8 in the PE + LAT group. The groups did not differ in terms of recurrence. Conclusions: Compared with the KT, the PE + LAT was associated with a shorter operative time, a more rapid return to normal activities, less pain, and a higher level of subjective satisfaction. We found that the PE + LAT was better than the KT for patients with early‐stage disease.
关键词： pilonidal sinus,karydakis,minimally invasive surgery,1,470‐nm diode laser,laser ablation,pit picking
更新于2025-09-23 15:19:57
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Coal Discrimination Analysis Using Tandem Laser-Induced Breakdown Spectroscopy and Laser Ablation Inductively Coupled Plasma Time-of-Flight Mass Spectrometry
摘要： The contribution and impact of combined laser ablation inductively coupled plasma time of flight mass spectrometry (LA-ICP-TOF-MS) and laser induced breakdown spectroscopy (LIBS) were evaluated for the discrimination analysis of different coal samples. This Tandem approach allows simultaneous determination of major and minor elements (C, H, Si, Ca, Al, Mg, etc), and trace elements (V, Ba, Pb, U, etc.) in the coal. The research focused on coal classification strategies based on principle component analysis (PCA) combined with K-means clustering, partial least squares discrimination analysis (PLS-DA), and support vector machine (SVM) for analytical performance. Correlation analyses performed from TOF mass and LIBS emission spectra from the coal samples showed that most major, minor, and trace elements emissions had negative correlation with the volatile content. Suitable variables for the classification models were determined from these data. The individual TOF data, LIBS data, and the combined data of TOF and LIBS, respectively, as the input for different models were analyzed and compared. In all cases, the results obtained with the combined TOF and LIBS data were found to be superior to those obtained with the individual TOF or LIBS data. The nonlinear SVM model combined with TOF and LIBS data provided the best coal classification performance, with a classification accuracy of up to 98%.
关键词： Principal component analysis,Support vector machine,Partial least squares discrimination analysis,Laser-induced breakdown spectroscopy,K-means clustering,Coal discrimination,Laser ablation inductively coupled plasma time of flight mass spectrometry
更新于2025-09-23 15:19:57
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Optimization of laser-target parameters for the production of stable lithium beam
摘要： A laser ion source coupled with a radio frequency quadrupole linac accelerator is being proposed as a suitable system for the production of a low energy, high-current stable lithium beam. In order to maximize the lithium yield, plasmas generated by laser ablation of different materials based on lithium (Li, LiOH, and LiNbO3) have been characterized by using a Faraday cup and an electrostatic ion analyzer in the time of flight configuration. A wide range of laser power density has been investigated (109–1012 W/cm2) using two Nd:YAG lasers operating at different wavelengths (1064 nm and 532 nm), pulse durations (6 ns and 17 ns), and maximum energies (1400 mJ and 210 mJ). This paper outlines the pros and cons of the investigated materials by studying how the ion energy, yields, and charge state distributions are modified when the laser power density is changed. Considerable attention has been paid to the higher charge states of oxygen, which may occur with the same mass-to-charge ratio of Li3+. The analysis has evidenced that LiNbO3 represents a valid target since it allows minimizing the O6+/7Li3+ ratio down to 2.5% by using a laser power density of 1.8 × 1010 W/cm2. For such a condition, a Li3+ current of 1.4 mA/cm2 has been measured.
关键词： oxygen contamination,laser ion source,lithium beam,charge state distributions,laser ablation
更新于2025-09-23 15:19:57
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Expansion dynamics and chemistry evolution in ultrafast laser filament produced plasmas
摘要： Laser ablation in conjunction with optical emission spectroscopy is a potential non-contact, standoff detection method for all elements in the periodic table and certain isotopes such as radionuclides. Currently, significant development efforts are on-going to use ultrafast laser filaments for remote detection of materials. The application of filaments is of particular interest in extending the range of stand-off capability associated with elemental and isotopic detection via laser-induced breakdown spectroscopy. In this study, we characterize the expansion dynamics and chemical evolution of filament-produced uranium (U) plasmas. Laser filaments are generated in the laboratory by loosely focusing 35 femtosecond (fs), 6 milli Joule (mJ) pulses in air. Two-dimensional spectrally-integrated and time-resolved imaging was performed to study hydrodynamics and evolution of U atomic and UO molecular emission in filament-produced U plasmas. Our results highlight that filament ablation of U plasmas gives a cylindrical plasma plume morphology with an appearance of plume splitting into slow and fast moving components at later times of its evolution. Emission from the slow-moving region shows no distinct spectral features (i.e. broadband-like) and is contributed in part by nanoparticles generated during ultrafast laser ablation. Additionally, we find U atoms and U oxide molecules (i.e. UO, UxOy) co-exist in the filament produced plasma, which can be attributed to the generation of low-temperature plasma conditions during filament ablation.
关键词： optical emission spectroscopy,Laser ablation,plasma chemistry,ultrafast laser filaments,uranium plasmas
更新于2025-09-23 15:19:57
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Metal organic frameworks composite Eu2O3@[Zn2(1,4-ndc)2dabco] synthesized by pulsed laser ablation in flowing liquid and its fluorescent sensing of fatty alcohol with different branch chains
摘要： This work reports the metal organic frameworks composite Eu2O3@[Zn2(1,4-ndc)2dabco] synthesized by pulsed laser ablation in flowing liquid. Powder X-ray Diffraction (PXRD) and SEM were used to characterize its structure and morphology. The results show that the Eu2O3 nanoparticles with the average particle size of 3.08 nm are uniformly distributed among the crystal and the BET specific surface area of the composite Eu2O3@[Zn2(1,4-ndc)2dabco] is 1087 m2/g. At 296 K, the adsorption capacities of C2H2 on composite are up to 117.3 cm3/g, which is larger than that of the compound [Zn2(1,4-ndc)2dabco]. The C2H6/CH4 selectivity of the composite Eu2O3@[Zn2(1,4-ndc)2dabco] is 25.9 and much higher than that of some familiar MOFs materials. Moreover, the composite Eu2O3@[Zn2(1,4-ndc)2dabco] can emit very intense characteristic fluorescence at 613 nm of Eu3t ion under ultraviolet radiation and can be used for detecting of fatty alcohols with different branch chains in fluorescence sensing because of its fluorescence intensity at 613 nm is sensitive to fatty alcohol with different carbon chains. The luminescence based sensing mechanism of the composite Eu2O3@[Zn2(1,4-ndc)2dabco] was discussed.
关键词： Flowing liquid,MOFs composites,Adsorption,Fatty alcohol with different branch chains,Pulsed laser ablation,Fluorescent sensing
更新于2025-09-23 15:19:57
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Photoluminescence and Raman spectroscopy of silicon thin films grown by laser ablation
摘要： Silicon thin films were prepared by Laser Ablation technique onto fused quartz substrates. The effect of thermal annealing on the silicon films and the pressure and temperature dependence show an unusual behavior of photoluminescence (PL) spectra of the silicon (Si) thin films. An intense PL energy band around 3.0 eV (400 nm) was observed at room temperature after thermal annealing. Raman spectra of the samples showed an asymmetric peak shifted to 517 cm?1; a broadening (7 cm?1) of the phonon line is also observed. These results agree quiet well with the relaxation of the q-vector selection rules for the Raman active optical phonons. The red-shifted asymmetric Raman line shape was fitted by using the phonon-confinement model, in order to estimate the size of the particles constituting the films.
关键词： Photoluminescence,Raman spectroscopy,Si-nanocrystals,Laser ablation
更新于2025-09-23 15:19:57
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Clear observation of the formation of nanoparticles inside the ablation bubble through a laser-induced flat transparent window by laser scattering
摘要： To understand the formation mechanism of nanoparticles via laser ablation in liquids direct observation of the dynamics inside the ablation bubble is essential. One powerful technique for this is small-angle X-ray scattering. Applying the laser-scattering technique in a similar context faces some difficulties, because, firstly the probe laser does not easily go into the bubble due to the curved bubble surface, and secondly the extremely weak scattering signal from inside the bubble is overwhelmed by the very strong reflection at the bubble surface. In this paper we solve those two problems by sending the probe laser into the bubble through a laser-induced flat transparent window, and demonstrate the clean observation of laser-scattering signals from the inside of the ablation bubble. We observe the signature of the formation of nanoparticles around the two areas inside the bubble, i.e., around the central area and apex inside the bubble. The scattering signals originating from the centre of the bubble persist throughout the entire growth and shrinkage stages of the bubble, while practically no scattering signals are found outside the bubble and this clearly implies that almost all nanoparticles are formed inside the bubble. Interestingly, the scattering signals originating from the apex inside the bubble gradually emerge after the bubble reaches the maximum size, and they become brighter as it further shrinks. Those findings are consistent with the scenario of nanoparticle formation obtained by small-angle X-ray scattering experiments.
关键词： nanomaterial synthesis,light scattering,nanoparticles,laser ablation,bubble dynamics
更新于2025-09-23 15:19:57
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PMMA-BN composites incorporated with Au nanoparticle fabricated by laser ablation
摘要： As a class of layered materials, two dimensional (2D) materials have attracted great attention all around the world due to their inherent use for next generation nano technology devices. We can see 2D materials including carbon in our daily life and at many places, for instance, graphite, diamond and so on. New study is also being conducted to produce new functional materials by combining 2D material and polymer. Hexagonal boron nitride (h-BN) which is one kind of 2D material is dispersed in Poly methyl methacrylate (PMMA) or poly styrene (PS). The composite material of h-BN coated with polymer shows an improvement in the properties such as the higher thermal conductivity and higher mechanical strength. In this study, the composite material of PMMA, h-BN and gold nanoparticles has been synthesized. Boron nitride nano-structures were prepared by nanosecond laser ablation in acetone and was carried out at room temperature with laser ablation time of 120 min. The PMMA films were made by PMMA granules dissolved in acetone solvent and then mix with h-BN and gold colloid solution. The prepared composite films were characterized by scanning electron microscopy (SEM), and UV-vis spectroscopy. Such type of unique 2D nano-composite materials make their mark for the future exploitation in electronics and nanocomposite-related applications.
关键词： gold nanoparticles,nanocomposite,2D materials,PMMA,laser ablation,h-BN
更新于2025-09-23 15:19:57