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Complementary Characterization of Laser-Induced Plasmas by Optical Emission Spectroscopy and Triple Langmuir Probe
摘要： In this article, we study the temporal evolution of the electron density and temperature of carbon laser-produced plasmas (LPP) using a combination of optical emission spectroscopy (OES) and the triple Langmuir probe (TLP) method. OES has been widely used to characterize LPPs but it is limited to distances relatively close to the target. On the other hand, the main advantage of TLP over the single-probe method is that it allows to obtain simultaneous measurements of electron temperature (Te) and density (Ne), without any voltage sweeping. In this article, we compare both techniques; measurements by OES were performed at distances from the target <1 cm, whereas the triple probe was employed for distances >5 cm. The plasma was generated by focusing nanosecond laser pulses onto a high purity graphite target placed inside a vacuum chamber. Our results show that the values of Te measured using both techniques predict decreasing exponential behavior. Ne determined by the spectral line Stark broadening in OES (<1 cm) was two orders of magnitude larger than that measured by the TLP (>5 cm). This difference in the electron density can be explained by radiative recombination and the presence of different kinds of plasma species detected by the TLP technique. The results show that both methods are complementary and their combination can be used to characterize LPP in a wide range of distances and timescales.
关键词： triple Langmuir probe (TLP),optical emission spectroscopy (OES),Laser-induced plasmas
更新于2025-09-11 14:15:04
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Oxygen Concentration Distribution Measurement of the Nozzle Flow Field by Toluene/Acetone Planar Laser-Induced Fluorescence
摘要： Planar laser-induced ?uorescence (PLIF) of toluene and acetone is performed for visualization of spatial distribution of oxygen in gas and oxygen mixing region in the nozzle ?ow ?eld. The principle of the calibration methods of oxygen concentration distribution is expounded in this paper. As the two tracers had different situations on oxygen quenching effect, the ratio of the ?uorescence images of the two tracers could be used to measure the oxygen concentration in the mixed area. In this way, the ratio of ?uorescence signal intensity of toluene to acetone was found to be linearly related to oxygen concentration. By using this calibration relationship, we can measure the oxygen concentration distribution of the nozzle ?ow ?eld with an accuracy of 12.6%. It indicates that this measurement method can be applied in a turbulent ?ow ?eld. The variation trend of oxygen concentration distribution in the nozzle ?ow ?eld can be analyzed by capturing multiple PLIF images in time sequence, which has the important reference value for the development of the nozzle burner ?ame.
关键词： nozzle ?ow ?eld,oxygen concentration distribution,?uorescence signal quenching,planar laser-induced ?uorescence,dual-tracers
更新于2025-09-11 14:15:04
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Laser-induced improvement in tribological performances of surface coatings with MoS2 nanosheets and graphene
摘要： To deal with the corrosive property of bio-oil, laser-induced coatings were synthesized on the typical cylinder liner rubbing surfaces. Two nano-additives including MoS2 nanosheets and graphene were introduced into the coatings. The tribological performances of the coated surfaces were tested on a multifunctional cylinder liner-piston ring tribometer. The surfaces before and after sliding were characterized with modern surface analysis technology including Raman spectra, X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and etc. The results show that the nickel-based coated surfaces can effectively prevent the corrosion of the bio-oil. In addition, the laser-induced coatings had better antifriction and antiwear performances than the corresponding traditional electroless plating coatings. With the introduction of MoS2 nanosheets or graphene, the tribological performances of the coatings were further enhanced. Laser irradiation increased the concentration of the nano-additives in the coatings and the thickness of the tribo-layers, which accounted for their outstanding tribological performances.
关键词： Laser-induced coating,Graphene,Bio-oil,MoS2 nanosheets,Tribological performance
更新于2025-09-10 09:29:36
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Mini-review: Laser-induced formation of microbubbles - biomedical implications
摘要： Recent work is summarized that shows how microbubbles may have potential utility in biomedical situations as (i) highly localized generators of intense whitelight in an aqueous environment, (ii) disruptors of matter in aqueous solution, (iii) essential precursors in laser-writing structures on substrates on which biological cells can be spatially aligned, and (iv) mediators in fabrication of hierarchical nano-structures that enhance signals in biological Raman spectroscopy. Indeed, microbubbles generated upon laser irradiation of surfaces have many more ramifications than originally thought, with implications in laser modification of surfaces producing either hydrophilicity or hydrophobicity. Many more possibilities remain to be explored and exploited.
关键词： Raman spectroscopy,biomedical applications,laser-induced formation,microbubbles,surface modification
更新于2025-09-10 09:29:36
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Flexible, multifunctional nanoribbon arrays of palladium nanoparticles for transparent conduction and hydrogen detection
摘要： A novel combination of nanostructuring techniques is undertaken to obtain a multifunctional material system consisting of planar arrays of nanoribbons of Pd nanoparticles (NPs) on polyethylene terephthalate (PET) substrates. The first stage was to prepare a laser-induced periodic surface structure (LIPSS) on the PET substrate, which electron microscopy revealed to be a large area, high coherence nanoripple pattern with spacing of (204 ± 1) nm and amplitude of (46 ± 9) nm. The second stage comprised NP (diameter 5 nm) deposition by orientating the nanostructured substrate to a Pd NP beam from a sputter gas phase aggregation source such that the substrate was partially shadowed by the ripple pattern (the incident angle with respect to the normal of the PET substrate was varied between 60 and 75o). This resulted in the formation of an array of NP ribbons (thickness ? 20 nm) on the ripple ridges, the mean ribbon width depending on the deposition incidence angle, thus confirming the shadowing effect. These planar arrays were studied as candidates for both flexible, transparent conductors and hydrogen sensors. Analysis of optical transmittance indicates that a mean inter-ribbon gap of above 100 nm is required in order to improve the average transmittance beyond 80 %. Four-probe electrical resistance measurements show these nanoribbon arrays to be electrically anisotropic structures whose sheet resistance is understood to be governed by the contact resistance between NPs. An additional functionality is proven for the fabricated substrates: reversible detection of hydrogen at a partial pressure above ? 60 ppm, with good electrical sensitivity in the dilute (?-hydride) regime.
关键词： palladium,Laser Induced Periodic Surface Structures,oblique deposition,nanoparticles,transparent conductors,hydrogen detection
更新于2025-09-10 09:29:36
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Kinetics of liquid-mediated crystallization of amorphous Ge from multi-frame dynamic transmission electron microscopy
摘要： The kinetics of laser-induced, liquid-mediated crystallization of amorphous Ge thin films were studied using multi-frame dynamic transmission electron microscopy (DTEM), a nanosecond-scale photo-emission transmission electron microscopy technique. In these experiments, high temperature gradients are established in thin amorphous Ge films with a 12-ns laser pulse with a Gaussian spatial profile. The hottest region at the center of the laser spot crystallizes in (cid:2)100 ns and becomes nano-crystalline. Over the next several hundred nanoseconds crystallization continues radially outward from the nano-crystalline region forming elongated grains, some many microns long. The growth rate during the formation of these radial grains is measured with time-resolved imaging experiments. Crystal growth rates exceed 10 m/s, which are consistent with crystallization mediated by a very thin, undercooled transient liquid layer, rather than a purely solid-state transformation mechanism. The kinetics of this growth mode have been studied in detail under steady-state conditions, but here we provide a detailed study of liquid-mediated growth in high temperature gradients. Unexpectedly, the propagation rate of the crystallization front was observed to remain constant during this growth mode even when passing through large local temperature gradients, in stark contrast to other similar studies that suggested the growth rate changed dramatically. The high throughput of multi-frame DTEM provides gives a more complete picture of the role of temperature and temperature gradient on laser crystallization than previous DTEM experiments.
关键词： liquid-mediated crystallization,dynamic transmission electron microscopy,amorphous Ge,kinetics,laser-induced crystallization
更新于2025-09-09 09:28:46
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Investigation on the dynamic characteristics of LIBS for heavy metal Mn in liquid matrix
摘要： Laser-induced breakdown spectroscopy in composition analysis of materials has many advantages over other analytical methods.Based on our Laser Induced Breakdown Spectroscopy (LIBS) survey system of heavy metals in the mixed solution and the optimum experimental parameters, we measured the integrated intensities of partial spectral lines of Mn when the ICCD gate delay time and the sample ?ow rate were ranged from 500ns to 2500ns, 35ml/min to 55ml/min respectively. With increasing the time delay, the electron temperature of the plasma decreases gradually, the electron density decreases ?rstly,then the change amplitude tends to be ?at.As the ?ow rate continue increasing,the electron temperature of plasma increases ?rstly, then the change tends to be ?at, the electron density increase gradually.The element particle density ratio of Mn at ?rst ionization state to ground state and Mn at ?rst ionization state are also obtained respectively. Finally, by comparing the experimental value of spectral line intensity ratio of Mn with the calculated value, the nonexistent conditions of local thermal equilibrium and self-absorption of laser plasma are veri?ed.It provides the suppuration for forward quantitative analysis of the trace heavy metal elements in liquid matrix.
关键词： Liquid matrix,Laser induced breakdown spectroscopy,Elements particle density ratio,Electron temperature,Electron density
更新于2025-09-09 09:28:46
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A hydrophobic ultralow refractive-index silica coating towards double-layer broadband antireflective coating with exceptionally high vacuum stability and laser-induced damage threshold
摘要： We report the fabrication of nanoporous silica coatings with tunable refractive indices by a one-step base-catalyzed sol-gel process using tetraethoxysilane as the precursor, hexamethylisilazane as the modifier at ambient conditions. The advantages of the present method are inexpensive, etchant-free and without high temperature calcination treatment. Importantly, porosity of the coatings can be tunable by changing the monomer ratio of the starting solution, which makes them suitable for top layer of broadband AR coatings. The tri-wavelength broadband AR coating with the refractive indices of the bottom and top layers as 1.27 and 1.16 was achieved on a fused silica substrate, which possessed high transmittance of 99.6%, 98.0% and 99.3% at 351 nm, 527 nm and 1053 nm, respectively. Moreover, the double-layer coating showed significant stability, when tested with polydimethylsiloxane pollution in vacuum for a week. In addition, LIDT of the double-layer coating was up to ca. 19.0 J cm?2 at a 6.3 ns laser pulse of 351 nm wavelength. This double-layer AR coating possesses excellent broadband AR performance, high LIDT, and excellent vacuum stability, which can open a new avenue to explore applications in high-power laser systems.
关键词： Antireflective coating,Laser-induced damage threshold,High-power laser system,Sol-gel,Vacuum stability
更新于2025-09-04 15:30:14