Laser-induced Breakdown Threshold Research Articles

Assessment of burner structure for methane-oxygen inverse diffusion flame based on laser detection: Reaction characteristics and soot analysis

The structure of a burner is a key issue of boilers and gasifiers in several industries. It significantly influences the flame formation and combustion reaction determining the mixing degree of fuel and oxidant. This study aims to explore the characteristics of flames at different angles and evaluate their advantages in specific applications. The present work explores the correlation between laser-induced breakdown threshold energy and flame temperature based on laser-induced breakdown spectroscopy (LIBS). Subsequently, the local structure and reaction characteristics of the flame at different burner angles (45, 60 and 90°) were investigated with simulation. The local equivalence ratio of the laminar flame was used to determine the distribution of reactants and components in the flame. The results indicated that the breakdown threshold energy was positively correlated with the temperature of the flame, and it was dependent on the gas concentration. With increased laser energy, the O/H ratio could be used as a function of the local equivalence ratio of the flame. In addition, the study of flame images and the spontaneous radiation of soot revealed that the C/H ratio in the flame reached the maximum value when the burner incident angle was 45°. Through simulation and experimental research, we found that the flame at 60° angle is the most stable, produces the least soot, has the highest combustion efficiency, and has better thermal radiation intensity.

Transient Laser-Induced Breakdown of Dielectrics in Ultrarelativistic Laser-Solid Interactions

For high-intensity laser-solid interactions, the absolute density and surface density gradients of the target at the arrival of the ultrarelativistic laser peak are critical parameters. Accurate modeling of the leading edge-driven target preexpansion is desired to strengthen the predictive power of associated computer simulations. The transition from an initial solid state to a plasma state, i.e., the breakdown of the solid, defines the starting point of the subsequent target preexpansion. In this work, we report on the time-resolved observation of transient laser-induced breakdown (LIB) during the leading edge of high-intensity petawatt-class laser pulses with peak intensities of up to 5.7×1021W/cm2 in interaction with dielectric cryogenic hydrogen jet targets. LIB occurs much earlier than what is typically expected following the concept of barrier suppression ionization. The observation is explained by comparing a characterization study of target-specific LIB thresholds with laser contrast measurements. The results demonstrate the relevance of the laser pulse duration dependence of LIB for high-intensity laser-solid interactions. We provide an effective approach to determine the onset of LIB and thereby the starting point of target preexpansion in other laser-target systems.Received 28 July 2022Revised 2 December 2022Accepted 16 December 2022DOI:https://doi.org/10.1103/PhysRevApplied.19.014070Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHigh intensity laser-plasma interactionsLight-matter interactionPlasma production & heating by laser beams, laser-foil, laser-clusterPhysical SystemsDielectricsRelativistic plasmasTechniquesFemtosecond laser irradiationLaser ablationOptical plasma measurementsPlasma PhysicsCondensed Matter, Materials & Applied PhysicsAtomic, Molecular & Optical

Influence of DC electric field on Nd:YAG laser-induced breakdown in gases

It is well known that pulsed laser can easily generate breakdown plasmas when the beam is focused. The laser-based gas breakdown phenomenon is caused by multiphoton ionization (MPI) and cascade ionization (CI) in a high-intensity electric field near the focal region. However, the phenomenon is complicated because it is affected by the purity of the gas and the focusing quality of the laser and optical systems. For a comprehensive understanding of the laser-induced breakdown phenomenon, the influence of an electric field on the threshold intensity of the laser-induced breakdown was investigated. The applied field disperses electrons generated in the focal area by the intense laser field, thereby increasing the laser-induced breakdown threshold intensity. The observed phenomenon is explained by a simple electron balance model.

Interstitial O2 and Si-H defects produced in fused silica during laser-induced damage

Fused silica irradiated with 6.8 ns 355 nm laser pulses is studied by micro-Raman scattering spectroscopy. Results show that, for laser fluences above the laser-induced breakdown threshold (Fth ~3.9 J/cm2), irradiation results in the formation of four laser-induced defect-related Raman bands centered at 1363, 1557, 1605.9 and 2330 cm−1. Bands centered on 1363, 1557 and 2330 cm−1 are attributed to Si = O, interstitial O2 and Si-H bond. However, defects giving rise to a broad band at 1605.9 cm−1 are unknown. Based on these results, we discuss physical processes occurring during the laser-induced fused silica breakdown, leading to the formation of Si-H bond and interstitial O2 and the fracture of fused silica.

Atomic and molecular LIBS spectra of Al alloys and composite materials for nanosecond and microsecond excitation

Spectral investigations in the UV-VIS range of selected Al alloys and composites, used in the construction of armament components as well as drones, were performed using LIBS technique. Two Nd:YAG lasers were applied: a short pulse 4 ns 60 mJ laser and a long pulse 200/400 (up to 1000) us (~ 2/4 up to 10 J) laser. In experiments with a short laser pulse only atomic spectra were observed while for long pulses, also molecular transitions have been recorded. Electron temperatures of created plasma were found on the base of Boltzmann law. Temperatures are clearly higher for short pulse excitation. Full Text: PDF ReferencesA. Miziolek, V. Palleschi and I. Schechter, Laser-Induced Breakdown Spectroscopy (Cambridge, Cambridge University Press 2006). CrossRef M. Sabsabi and P. Cielo, "Quantitative Analysis of Aluminum Alloys by Laser-Induced Breakdown Spectroscopy and Plasma Characterization", Appl. Spectrosc. 49, 499 (1995). CrossRef D.L. Death, A.P. Cunningham, and L.J. Pollard, "Multi-element analysis of iron ore pellets by Laser-induced Breakdown Spectroscopy and Principal Components Regression", Spectrochim. Acta B, 63, 763 (2008). CrossRef S. Laville, M. Sabsabi and F. Doucet, "Multi-elemental analysis of solidified mineral melt samples by Laser-Induced Breakdown Spectroscopy coupled with a linear multivariate calibration", Spectrochim. Acta B, 62, 1557 (2007), CrossRef D.M. Surmick, C.G, Parigger, "Aluminum Monoxide Emission Measurements in a Laser-Induced Plasma", Applied Spectroscopy, 2015, V.68, No.9, P.992-996. CrossRef J.B. Sirven, B. Bousquet, L. Canioni and L. Sarger,"Laser-Induced Breakdown Spectroscopy of Composite Samples: Comparison of Advanced Chemometrics Methods", Anal. Chem. 78, 1462 (2006). CrossRef E.J. Judge, G. Heck, E.B. Cerkez and R. J. Levis, "Discrimination of Composite Graphite Samples Using Remote Filament-Induced Breakdown Spectroscopy", Anal. Chem. 81, 2658 (2009). CrossRef L.M. Cabalin and J.J. Laserna, "Experimental determination of laser induced breakdown thresholds of metals under nanosecond Q-switched laser operation", Spectrochim. Acta B, 53, 723 (1998). CrossRef T.A. Labutin, A.M. Popov, V.N. Lednev and N.B. Zorov, "Correlation between properties of a solid sample and laser-induced plasma parameters", Spectrochim. Acta B, 64, 938 (2009). CrossRef J.S. Cowpe, R.D. Moorehead, D. Moser, J.S. Astin, and S. Karthikeyan, "Hardness determination of bio-ceramics using Laser-Induced Breakdown Spectroscopy", Spectrochim. Acta B, 66, 290 (2011). CrossRef G. Cristoforetti, , S. Legnaioli, V. Palleschi, A. Salvetti, and E. Tognoni, "Effect of target composition on the emission enhancement observed in Double-Pulse Laser-Induced Breakdown Spectroscopy", Spectrochim. Acta B, 63, 312 (2008). CrossRef

Spatiotemporal distributions of plasma and optical field during the interaction between ultra-short laser pulses and water nanodroplets

The transient changes of free electron density distribution and light field intensity during the interaction between the femtosecond Gaussian laser pulses and millimeter scale water droplets are studied. Based on the nonlinear Maxwell's equations and the ionization rate equation, a transient coupled model is proposed to describe the laser plasma produced in water droplet. The changes of electron density and light field with time are obtained by the finite element method. The calculation results show that the laser induced breakdown threshold in the droplet is about 2 TW/cm2, one quarter of that in a boundaryless water medium under the same condition. We find that the region of plasma generated in the droplet will move along the laser direction at first, however, when the incident laser intensity becomes larger, it will move in the direction opposite to the laser beam propagation and the plasma shielded effect becomes more obvious. The laser beam converged by the droplet focuses outside the droplet, and its power density is five times larger than that of the incident laser. There happen the laser pulse duration compression and waveform distortion at the focus point due to the plasma absorption, and the absorption energy increases with the laser intensity increasing and reaches a saturation finally. We expect the model and calculation results to be able to be used for the study of laser pulse propagation in cloud or rain, the precision control of droplet by laser or eye surgery by laser, and other laser technology applications.

Laser induced damage studies of LiNbO_3 using 1030-nm, ultrashort pulses at 10-1000 kHz

R-on-1 laser induced breakdown thresholds are reported for a wide range of lithium niobate crystals at laser parameters relevant for state-of-the-art optical parametric amplifiers pumped with high repetition rate ultrafast Yb-laser sources. The samples included uncoated and anti-reflection coated, blank and periodically poled MgO-doped congruent crystals and were measured at repetition rates between 10 and 1000 kHz, pulse durations of 330 fs and 1 ps, and temperatures between 20 and 170 °C.

Quantitative measurement of electron number in nanosecond and picosecond laser-induced air breakdown

Here we present quantitative measurements of total electron numbers in laser-induced air breakdown at pressures ranging from atmospheric to 40 barg by 10 ns and 100 ps laser pulses. A quantifiable definition for the laser-induced breakdown threshold is identified by a sharp increase in the measurable total electron numbers via dielectric-calibrated coherent microwave scattering. For the 10 ns laser pulse, the threshold of laser-induced breakdown in atmospheric air is defined as the total electron number of ∼106. This breakdown threshold decreases with an increase of pressure and laser photon energy (shorter wavelength), which is consistent with the theory of initial multiphoton ionization and subsequent avalanche processes. For the 100 ps laser pulse cases, a clear threshold is not present and only marginal pressure effects can be observed, which is due to the short pulse duration leading to stronger multiphoton ionization and minimal collisional avalanche ionization.

On the measurement of laser-induced plasma breakdown thresholds

The breakdown threshold of a gas exposed to intense laser-radiation is a function of gas and laser properties. Breakdown thresholds reported in the literature often vary greatly and these differences can partially be traced back to the method that is typically used to determine breakdown thresholds. This paper discusses the traditional method used to determine breakdown thresholds and the potential errors that can arise using this approach, and presents an alternative method which can yield more accurate data especially when determining breakdown thresholds as functions of gas pressure.

Pressure Dependence of Laser-Induced Dielectric Breakdown in Water

The effects of pressure on laser-induced breakdown events at superthreshold irradiances in water were investigated over a range of pressures from 0 to 1380 bar. Breakdown events were generated using 5-ns Nd:YAG laser pulses of wavelength 532-nm. Observations of breakdown events were made using imaging and single detector techniques. Applications for use as a static and/or acoustic pressure sensor were explored. Using imaging techniques over a range of static pressures from 0 to 275 bar, it was observed that the laser-induced breakdown threshold increased with increasing pressure. An ability to infer acoustic pressure via optical breakdown techniques using imaging was demonstrated. Single detector measurements over the same pressure range were observed to follow a similar trend.

Measurement of laser-induced breakdown threshold intensities of high-pressure gasses and water droplets to determine the number density of an aerosol

The laser-induced breakdown threshold intensities of high-pressure gasses as a function of pressure were measured. The breakdown threshold intensity of N 2 gas was found to be much higher than those of He and Ar gasses at a gas pressure of 2.0 MPa. It was also 7 to 11 times higher than that of aerosol droplets, and is sufficiently high to allow the number density of droplets to be measured in a high-pressure aerosol by laser-induced breakdown.

Transient phenomena in the dielectric breakdown of HfO2 optical films probed by ultrafast laser pulse pairs

The laser induced breakdown threshold of HfO2 films is studied with single pairs of pulses of variable delay and 50 fs and 1 ps pulse duration. Two distinct transient regimes are observed that can be related to the relaxation of the electron density from the conduction band via an intermediate state to the valence band. The experimental results are in good agreement with a theoretical model that assumes occupation of mid gap states after the first pulse on a time scale of several tens of picoseconds and subsequent decay of this population via recombination with holes in the valence band on a time scale of several tens of milliseconds.

Enhanced optical breakdown in KB cells labeled with folate-targeted silver-dendrimer composite nanodevices

Enhanced optical breakdown of KB tumor cells folate-targeted with silver-dendrimer composite nanodevices (CNDs) is described. CNDs [(Ag 0) 25-PAMAM_E5.(NH 2) 42(NGly) 74(NFA) 2.7] were fabricated by reactive encapsulation, using a biocompatible template of dendrimer–folic acid (FA) conjugates. Preferential uptake of the folate-targeted CNDs (of various treatment concentrations and surface functionality) by KB cells was visualized with confocal microscopy and transmission electron microscopy. Intracellular laser-induced optical breakdown threshold and dynamics were detected and characterized by high-frequency ultrasonic monitoring of resulting transient bubble events. When irradiated with a near-infrared, femtosecond laser, the CND-targeted KB cells acted as well-confined activators of laser energy, enhancing nonlinear energy absorption, exhibiting a significant reduction in breakdown threshold and thus selectively promoting intracellular laser-induced optical breakdown. From the Clinical Editor This study presents a novel method to selectively destroy cancer cells by combining biochemical targeting with topical laser irradiation. A human epidermoid cancer cell line was targeted with folated silver-dendrimer composite nanodevices and the labeled cancer cells were subsequently destroyed by the microbubbles generated due the enhanced energy uptake of the silver nanoparticles from the laser irradiation, as compared to unlabeled cells.

Laser-induced ionization and intrinsic breakdown of wide band-gap solids

A simple scaling of bulk laser-induced breakdown threshold for wide band-gap solids is derived on the basis of a recent modification of the Keldysh photo-ionization model [43, 46]. Contrary to most traditional models, the modification is based on rigorous energy dependence of reduced effective electron–hole mass. The dependence leads to a specific ionization regime with an extremely high ionization rate resulting in intensive generation of conduction-band electrons. The regime is characterized by a well-determined threshold intensity that is proposed to be associated with the threshold of bulk intrinsic laser-induced breakdown (LIB) by visible and near-infra-red laser radiation. That allows deriving dependence of LIB threshold on laser and material parameters. The presented model provides explanation for the experimental results on LIB thresholds that have not received theoretical interpretation. In particular, it reproduces empirical dependence of breakdown threshold on the average inter-atomic spacing derived from the experimental data. The LIB threshold evaluated from the presented model is very close to experimental data on bulk LIB by tightly focused beams in wide band-gap solids.

Surface ablation of lithium tantalate by femtosecond laser

We report measurements of the laser induced breakdown threshold in lithium tantalate with different number of pulses delivered from a chirped pulse amplification Ti: sapphire system. The threshold fluences were determined from the relation between the diameter D 2 of the ablated area and the laser fluence F 0. The threshold of lithium tantalite under single-shot is found to be 1.84 J/cm 2, and the avalanche rate was determined to be 1.01 cm 2/J by calculation. We found that avalanche dominates the ablation process, while photoionization serves as a free electron provider.

Laser-induced breakdown threshold and fracture versus the nanostructure of two-phase glass

The radiation hardness and mechanical strength of single-and two-phase glasses are studied for the case when nanosecond laser pulses (λ= 1.06 μm, τ0.5 ≈ 12.5 ns) are focused inside the material. Laser interferometry is applied to measure the displacement of the free surface, find optical breakage thresholds, and carry out the fractographic analysis of damaged regions. It is shown that breakdown channels and damage regions develop in a nonlinear manner according to optical breakdown mechanisms, changing each other with an increase in the laser energy. The strength of the two-phase glass is found to be more than four times that of the single-phase glass, although their elastic properties differ insignificantly. Such a considerable difference in the hardness of these materials with chemically similar constitutents is attributed to the presence of the double-lattice nanometer-scale structure of the two-phase glass.

Decomposition of KH2PO4 crystals during laser-induced breakdown

The structure of KH2PO4 single crystals (so-called KDP) irradiated with ∼3ns, 355 nm laser pulses with fluences above the laser-induced breakdown threshold is studied by a combination of Raman scattering, photoluminescence, and soft x-ray absorption spectroscopies. We compare spectra from the as-grown material, surface and bulk laser-induced damage sites, as well as from KPO3 references. Results show that irradiation with fluences above the laser-induced breakdown threshold leads to decomposition of KDP at surface damage sites but not at bulk damage sites. New spectroscopic features are attributed to dehydration products. For the laser irradiation conditions used in this study, the decomposed near-surface layer absorbs photons at ∼3.4eV (364 nm). These results may explain the recently reported fact that surface laser damage sites in KDP crystals tend to grow with subsequent exposure to high-power laser pulses, while bulk damage sites do not.

Different tendencies of breakdown threshold on pulse duration in the subpicosecond regime in fused silica

Measurements of the single-shot laser-induced breakdown threshold in bulk fused silica were performed at a wavelength of 800 nm for pulse durations ranging from 240 fs to 2.5 ps. Objectives with different numerical apertures (NAs) were used to focus the laser pulse into the sample. It was found that the threshold started to increase with the decrease of the pulse duration when it was less than 700 fs for effective NA = 0.126, while for effective NA = 0.255 it kept decreasing. Numerical simulations based on the nonlinear propagation model revealed that the generated plasma played an important role in the breakdown process and was responsible for the different tendencies observed in this study. Moreover, it was noticeable that the trend of the threshold on pulse duration was sensitive to the assumed threshold electron density, which implied that various definitions of breakdown might lead to different tendencies of the threshold.

Effets tissulaires et mécaniques observés lors de l’expérimentation d’un microkératome laser femtoseconde pour la chirurgie réfractive cornéenne

Despite progress in mechanical microkeratomes used in refractive surgery, mechanical complications during cutting of the cornea still occur. Cutting by laser could reduce these complications and to date, the femtosecond laser is the only potential candidate for this purpose. Our study reports preliminary results with a femtosecond microkeratome for cutting porcine corneas ex vivo. We first examined the fundamental principles of the interaction between the femtosecond laser and the corneal stroma, including the volume of tissue lesions, the laser breakdown threshold of the stroma and the laser ablation selectivity. We then analyzed the quality of cutting corneal flaps with the laser, focusing on collateral tissue effects and the roughness of the interfaces observed both histologically and with scanning electron microscopy. The photoablative and photodisruptive effects were very similar with the femtosecond laser. This characteristic is specific to ultrashort impulsion photodisruptor lasers and allows for a very precise surgical procedure. The laser-induced breakdown threshold of porcine corneal stroma was found to be 0.55 J/cm2. Collateral tissue lesions were on the submicrometer level. The roughness of the stromal bed was optimal for postage stamp cutting, providing very many contiguous points of impact which were as spherical as possible. Corneal photodisruption with a femtosecond laser is reproducible and extremely accurate. The optomechanical parameters involved with this technique require great technological skill and should be placed in experienced hands.

Sub-50-fs laser retinal damage thresholds in primate eyes with group velocity dispersion, self-focusing and low-density plasmas.

In vivo retinal injury studies using sub-50-femtosecond laser pulses in the near-infrared must consider nonlinear effects such as group velocity dispersion (GVD), self-focusing, laser-induced breakdown (LIB) and low-density plasmas (LDPs). In this paper we present the results of our theoretical calculations of nonlinear effects and our experimental measurements for the visible lesion thresholds in live eyes. We compare these values with the measured LIB and LDP thresholds in an artificial eye. All three thresholds were measured with and without pre-chirping the input pulse to compensate for GVD effects. We recorded the minimum visible lesion (MVL) thresholds in vivo for sub-50-fs laser pulses, with and without pre-chirping the input pulses. In addition, we measured the LIB and LDP thresholds, with and without pre-chirping, within an artificial eye. Different degrees of pre-chirping were required to give optimal compensation for GVD in the live eye and the artificial eye. Probit analysis was used on all data, and comparisons among thresholds were made, to determine the effects on the three thresholds of chirp compensation for GVD. Results of our nonlinear modeling and calculations for GVD compensation, self-focusing, LIB, and low-density plasmas were compared with our experimental results using live eyes and the artificial eye. The damage threshold in live eyes dropped in energy from 0.25 microJ, for the flat-phase input, to 0.17 microJ when optimally chirped pulses were used, while the LIB threshold was reduced from 0.29 microJ to 0.19 microJ with optimally chirped pulses. The LDP threshold dropped from 0.21 microJ to 0.14 microJ with the pre-chirped pulse. At 44 fs, these energies produced peak powers at least twice the calculated critical power that produces nonlinear self-focusing and beam collapse, for propagation of non-aberrated gaussian beams in a uniform medium. Based on our measurements of the MVL thresholds, with and without GVD compensation, we conclude that the visible lesion thresholds produced by 44 fs pulses in rhesus eyes are increased in energy due to GVD. The MVL ED50 was reduced by one third when the pulse was pre-chirped to compensate for GVD in the eye. This reduction in amplitude also holds true in the artificial eye for the LIB ED50 bubble thresholds and the LDP ED50 plasma channels, when using pre-chirped pulses versus non-chirped pulses. We also conclude from the data presented that low-density plasmas, and not LIB cavitation bubbles, are the probable mediating factor at the visible lesion thresholds observed within live eyes, for pulse durations at and below 50 fs. Therefore, the plasma channel created by LDPs is the major damage mechanism, if not the only damage mechanism, at MVL threshold energies for these pulse durations.