Including Pulse Energy Research Articles

Elemental quantitation and evaluation of hydrocarbon in shale using fiber-optic laser induced breakdown spectroscopy

To meet the demands of in situ analysis, a fiber-optic laser-induced breakdown spectroscopy (FO-LIBS) system was established to predict the elemental concentrations and pyrolytic parameters. The key parameters, including pulse energy, gate delay, type of surrounding gas, and flow rate of gas, were optimized to improve the signal-to-noise ratio of the spectral lines, and the evolution characteristics of the plasma morphology in different gas atmospheres were investigated. Under the optimized experimental conditions, C, H, Si, Ca, Fe, and Mg were calibrated using pellet samples based on partial least squares regression, and the average relative prediction error of the natural samples was lower than 10%. In addition, the support vector regression method was utilized to predict pyrolytic parameters such as TOC, Pg, and Tmax with the R2 of all calibration curves being higher than 0.97. The abundance and generation potential of hydrocarbons were evaluated using the predicted TOC and Pg, and Tmax could contribute to the thermal maturity of the kerogen.

Influence of working parameters on multi-shot femtosecond laser surface ablation of lithium niobate

This paper presents an experimental investigation on the ultrashort pulsed laser ablation of 128° Y-cut Lithium Niobate (LiNbO3) using multi-shot fs-laser pulses at different pulse repetition frequencies (1, 10 and 100kHz). The ablation threshold fluence was observed to rapidly decrease as the number N of incident laser pulses increased, regardless of the repetition frequency. This behavior, compatible with the incubation effect, was accurately modeled by a power law. The calculated single pulse ablation threshold Fth,1=1.98±0.15J/cm2 is consistent with values reported in existing literature. The incubation coefficient S∗ appears to be independent of the repetition frequencies. In contrast, the asymptotic ablation threshold Fth,∞ decreased as the repetition frequency was increased. The study delves deeper into the impact of laser operational variables, including pulse energy, repetition frequency, total pulse count, and scanning speed, on the surface roughness and milled depth of fs-laser micromilled zones on LiNbO3 substrates. A discernible trade-off between achieving control over the obtained depth and the surface finish of the process was identified, providing valuable insights for achieving precise control over fs-laser processing of LiNbO3 surfaces.

Crystalline / glass nanoscale chemical separation induced by femtosecond laser pulses in aluminosilicate glass

An aluminosilicate glass with a molar composition of 60%Al2O3–40%SiO2 fabricated by the aerodynamic levitation technique was irradiated in volume using an infrared femtosecond laser. Optical retardance was observed and measured upon a wide range of varying laser parameters including pulse energy, repetition rate, pulse duration, writing speed, and laser polarization. A similar analysis was performed in silica glass (Suprasil CG) taken as a reference. We measured retardance values as high as 100 nm in the aluminosilicate glass, which is approximately 2x higher than previously investigated aluminosilicate glasses. Raman spectroscopy and electron microscopy techniques revealed the presence of an orientable lamellar structure, commonly referred to as nanogratings, composed of alternate SiO2-enriched amorphous layers with Al2O3-enriched ones. The latter are essentially crystallized in a 3Al2O3:2SiO2 Mullite phase. This internal structuring, the first one in a congruent glass, brings additional insights into the mechanisms leading to nanogratings formation, and may be proved useful for future glass-based functional optical devices with very large thermal stability.

Photon Diagnostics for the High-Gain THz FEL at PITZ

Research and development of an accelerator-based THz source prototype for pump-probe experiments at the European XFEL are ongoing at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). Proof-of-principle experiments have been performed to generate a high-gain THz Free-electron Laser (FEL) based on the Self-Amplified Spontaneous Emission scheme. The FEL radiation pulses with a central wavelength of about 100 μm (3 THz) and single pulse energy of several tens μm can be generated. In this paper, we present and discuss the photon diagnostic setup for the THz FEL together with examples of diagnostic results, including pulse energy and an FEL gain curve. The upgraded photon diagnostic setup, capable of measuring pulse energy, transverse distribution, and spectral distribution, is expected to be operational in the spring of 2023.

A highly automated apparatus for ultra-fast laser ablation studies.

We present a novel experimental apparatus that can be used for extensive systematic studies of (single- and multi-shot) ultra-short laser pulse ablation. It is fully automated and generates a large number of ablation sites in a short time on a small sample surface area. For each site, the apparatus takes four in situ images: an image of the incident ablation beam (to determine pulse energy), a white light reference image of the pristine sample site, an image of the reflected ablation spot, and a white light image of the ablated sample site. The setup can perform ablation experiments as a function of many parameters, including pulse energy, pulse duration, number of pulses, time between pulses, and focus size. As a proof of concept, we present example results on single-shot ablation off crystalline silicon. Using only data acquired in situ in the presented setup, we determine the single-shot ablation threshold as a function of pulse duration and verify the threshold value using optical interferometric profilometry. The values we found agree well with literature values.

Liquid-Phase Non-Thermal Plasma Discharge for Fuel Oil Processing

The non-thermal plasma pyrolysis of fuel oil, under the action of low-voltage electric discharges in the liquid phase, has made it possible to develop a new process to obtain valuable petrochemical products. In this study, the main parameters, including pulse energy and the time of impact on the non-thermal plasma pyrolysis process, are studied. The main components of the obtained gaseous products are hydrogen (27.6–49.6 mol%), acetylene (33.6–49.1 mol%), ethylene (6.9–12.1 mol%), methane (3.9–9.1 mol%), and hydrocarbons C3-C5 (3.8–9.3 mol%). Increasing the capacity of electric discharges leads to an increase in the content of acetylene in the gas phase to 49.1 mol% and a decrease in energy costs for the production of gaseous products.

Laser-induced alloy nanoparticles on Au-Sn thin layers

The paper analyses the process of Au-Sn alloy nanoparticles (ANPs) formation by laser-induced dewetting of thin intermetallic layers for the first time. Tests were carried out for several samples with different Au-Sn atomic ratios and different total layer thicknesses (7.5 and 15 nm). The initial parameters of the samples were verified by spectroscopic ellipsometry (SE). To develop the experiment, a nanosecond ytterbium fiber laser (Yb:glass) with a wavelength of 1064 nm was used. The study was carried out both with the use of single laser pulses as well as raster scanning of the given surface. The use of two modes allowed to determine the impact of key process parameters (including pulse energy, degree of pulse overlap and laser fluency) on the formation, evolution, morphology, distribution and chemical composition of the obtained structures. The optimal conditions for the formation of Au-Sn ANPs were established.The samples were analysed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The chemical composition was analysed by means of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The optical properties of the obtained ANPs were determined by spectroscopic ellipsometry and the morphology and chemical composition were examined by transmission electron microscopy (TEM).

Investigation of melting rate in welding of IN738 Nickel-based superalloy by Nd:YAG pulsed-laser method

In this study, the effect of different parameters of pulsed Nd:YAG laser welding, including pulse energy, pulse frequency, pulse duration, and welding speed on the melting rate of IN738 Nickel-based superalloy, was investigated. The results of this study were obtained based on the modification of a formula for calculating the melting rate of welding by pulse method (pulse overlap). According to this formula, effective pulse energy (EPE) affected by pulse overlap, has a significant effect on the melting rate. So that by decreasing the amount of EPE (increasing the pulse overlap), the melting rate increases to 67% overlap and then decreases due to the reduction of the heating rate through heat transfer to the base metal. The study of the effect of pulse laser parameters showed that pulse energy, pulse overlap, and pulse duration have the greatest effect on melting rate, respectively.

Lasers for stone treatment: how safe are they?

To update laser lithotripsy advances in regard to new laser types and technologies as well as review contemporary laser safety concerns. The high prevalence of urolithiasis and the continuing miniaturization of scopes has encouraged the growth of laser lithotripsy technology. The holmium:yttrium-aluminum-garnet (Ho:YAG) laser has been used for over 20 years in endourology and has been extensively studied. Holmium laser power output is affected by a number of factors, including pulse energy, pulse frequency, and pulse width. Several recent experimental studies suggest that the new dual-phase Moses 'pulse modulation' technology, introduced in high-power laser machines, carries a potential to increase stone ablation efficiency and decrease stone retropulsion. A newly introduced thulium fiber laser (TFL) has been adapted to a very small laser fiber size and is able to generate very low pulse energy and very high pulse frequency. Both of these technologies promise to play a larger role in laser lithotripsy in the near future. However, more experimental and clinical studies are needed to expand on these early experimental findings. Even though laser lithotripsy is considered safe, precautions should be taken to avoid harmful or even catastrophic adverse events to the patient or the operating room staff. The Ho:YAG laser remains the clinical gold standard for laser lithotripsy for over the last two decades. High-power Ho:YAG laser machines with Moses technology have the potential to decrease stone retropulsion and enhance efficiency of laser ablation. The new TFL has a potential to compete with and perhaps even replace the Ho:YAG laser for laser lithotripsy. Safety precautions should be taken into consideration during laser lithotripsy.

Systematic experimental study on a highly efficient terahertz source based on two-color laser-induced air plasma

In this paper, highly efficient terahertz radiation generated by two-color femtosecond laser-induced air plasma is reported. A number of variables that can obviously influence terahertz generation and detection have been investigated systematically. The dependence on experimental parameters, including pulse energy, the rotation angle of beta–barium boron oxide (BBO) crystal, the distance between BBO crystal and laser-induced plasma, focal length, chopper frequency, and detection angle are presented, and the optimal values of these parameters have also been obtained experimentally. Finally, a highly efficient terahertz source has been achieved and can be utilized to carry out further investigation on terahertz sensing, spectroscopy, and imaging.

Highly stable and self-started all-fiber Yb3+ doped fiber laser mode-locked by chirped pulse spectral filtering and nonlinear polarization evolution

Without discrete optical components influencing the fiber format, all-fiber mode-locked laser has tremendous potential practical applications due to its advantages of better stability, alignment free, and better compaction. All-fiber laser mode-locked by nonlinear polarization evolution（NPE) can obtain good performances in terms of pulse duration and spectrum. But the effective saturable absorption mirror can be overdriven at high peak power, which leads to multiple pulses, limiting the output pulse energy. And there is a trade-off between avoiding overdriving the NPE and ease of self-starting. In addition, the polarization of the pulse propagating in a long fiber is so sensitive to the environment vibration that it is difficult to implement a stable lone-time operation.All-fiber ring laser mode-locked by NPE alone is analyzed and realized. The simulation results show that even a polarization vibration of up/38 can break the mode-locking completely. Experimentally, after carefully adjusting, single-pulse mode-locking is achieved with the spectrum centered at 1053.4 nm and a maximum pulse energy of 82 pJ. But the output parameters change continually during operating. After 60 min, the mode-locking is broken. The conclusion is obtained that instability and unreliability of self-starting are inevitable for such a laser.Here, we show significant improvements of the pulse energy, operating stability, and self-starting reliability from an all-fiber Yb-doped mode-locked fiber laser. The laser is mode-locked by NPE combined with chirped pulse spectral filtering（CPSF). In order to easily self-start and stabilize mode locking, a spectral filter is employed in the all-normal group velocity dispersion NPE cavity to provide additional amplitude modulation. Combined effects of NPE and CPSF result in desirable pulse output, desirable operating stability, and reliable self-starting simultaneously. Stable mode-locking centered at 1053 nm is achieved with a 3 dB spectral bandwidth of 9.1 nm and pulse duration of 17.8 ps. The average output power is 66.9 mW at a repetition rate of 15.2 MHz, corresponding to a pulse energy of 4.25 nJ. Especially, high operating stability and easily one-button self-starting are achieved simultaneously. The fluctuations of output parameters including pulse energy, pulse duration, and spectrum are within 0.3% during 150-min operation. Self-starting reliability is tested. The testing time lasts two weeks. During the two weeks, the laser is turned off and turned on 48 times by using a power supplying button, without any adjustment. And the re-turned on intervals change randomly. Each time, the mode-locking can start itself. The repeatabilities of output parameters including pulse energy, pulse duration, and spectrum are within 0.55%.

Intense Pulsed Light Sintering of Copper Nanoink for Conductive Copper Film

Conducting electrodes and films are becoming increasingly important for the printed electronics which can be applied in various fields such as RFID tags, photovoltaics, display and PCB. And copper nanoparticle inks serve as an attractive potential replacement to silver nanoparticle inks because its low cost and good electrical conductivtiy.In this paper, the commercial copper nanoparticle powder with oxide shells were dispersed in the solvent of ethylene glycol. Poly (N-vinylpyrrolidone) (PVP K30) was added to the solvent as capping materials. The prepared copper ink was spin-coated on glass substrate under ambient conduction. Then, the deposited Cu ink was sintered by an intense pulsed light (IPL) system. The sintering effects were investigated with different sintering conditions including pulse energy and pulse duration. The resulting electrical resistivity was 94.1uΩ·cm which is about fifty times as high as that of bulk copper. The high resistivity may be mainly attributed to the porosity of sintered film. Also, crystal phase analysis was performed using x-ray diffraction (XRD) and was found the XRD peaks corresponding to cuprous oxide disappeared after IPL sintering. It was believed that PVP reduced the copper oxide to copper in the process of IPL sintering.

High aspect ratio, high-quality microholes in PMMA: a comparison between femtosecond laser drilling in air and in vacuum

Microholes, especially high aspect ratio, high-quality microholes with small diameters (<100 μm), have broad applications. However, it is very difficult for traditional drilling methods to obtain deep microholes, especially with aspect ratios of over 50:1. Femtosecond lasers provide a promising solution for efficient drilling of deep microholes with high-precision material removal, reduced recast/microcracks, minimized heat-affected zones, and the absence of plasma-shielding effects. In this work, a comparison study of high aspect ratio, high-quality microholes fabricated in a poly(methyl methacrylate) (PMMA) bulk substrate with the ambient pressure adjusted from 105 Pa (air) down to 1 Pa (vacuum) is presented. High aspect ratio (over 100:1) microholes were obtained in a vacuum environment. The contrast between microhole evolution in air and in vacuum was investigated. The results indicate that efficient energy propagation and easy ejection of ablated material/plasma are probably the most important benefits of drilling microholes in vacuum. The dependence of microhole shapes on different fabrication parameters, including pulse energy and ambient pressure, was investigated to quantitatively reveal the underlying mechanisms. The enhanced drilling effect in vacuum was only found in a high pulse energy region (E p > 20 μJ), and it becomes saturated when the ambient pressure was reduced to ~102 Pa at a pulse energy of 50 μJ. Drilling microholes in a vacuum provides a simple and effective way of rapidly fabricating high aspect ratio, high-quality microholes.

Update on lasers in urology 2014: current assessment on holmium:yttrium–aluminum–garnet (Ho:YAG) laser lithotripter settings and laser fibers

The purpose of the study was to review the existing literature on holmium:yttrium-aluminum-garnet laser lithotripsy regarding lithotripter settings and laser fibers. An online search of current and past peer-reviewed literature on holmium laser lithotripsy was performed on several databases, including PubMed, SciElo, and Google Scholar. Relevant studies and original articles about lithotripter settings and laser fibers were examined, and the most important information is summarized and presented here. We examine how the choice of lithotripter settings and laser fibers influences the performance of holmium laser lithotripsy. Traditional laser lithotripter settings are analyzed, including pulse energy, pulse frequency, and power levels, as well as newly developed long-pulse modes. The impact of these settings on ablation volume, fragment size, and retropulsion is also examined. Advantages of small- and large-diameter laser fibers are discussed, and controversies are highlighted. Additionally, the influence of the laser fiber is examined, specifically the fiber tip preparation and the lithotripter settings' influence on tip degradation. Many technical factors influence the performance of holmium laser lithotripsy. Knowing and understanding these controllable parameters allows the urologist to perform a laser lithotripsy procedure safely, efficiently, and with few complications.

Beam shaping and compensation for high-gain Nd:glass amplification

Beam shaping and compensation are reported for a high Nd:glass amplification system based on the liquid crystal spatial light modulation technique. As a typical application, a signal Gaussian beam of 1 nJ, with a pulse width of 3 ns, was amplified to 5 J with a flat-top intensity distribution. A spot modulation of 1.41 on the dimension of 50 mm × 50 mm was obtained. The minor beam distortion was further eliminated by applying a closed loop control. Most parameters including pulse energy, frequency, spot intensity distribution, etc., can be measured and calculated simultaneously via this proposed system. Moreover, the structure of image transfer was confirmed to be capable of maintaining high-quality image transmission in the amplification process.

A study on laser-fibre coupling efficiency and ablation rate in femtosecond laser deep microdrilling

Laser microdrilling is a common micromachining operation in many industrial applications. This paper presents a new laser microdrilling technique in which a hollow-core fibre is employed to transmit femtosecond laser pulses to the target position. The coupling efficiency between the laser and the fibre is investigated and found to be strongly related to pulse energy and pulse duration. A parametric study on the ablation rate indicates that in microdrilling of a stainless steel (type 303), the operating parameters including pulse energy, pulse duration, sample thickness, focal length and sample-fibre distance can affect the ablation rate. The experimental results show that the new technique developed in this study is feasible to conduct microdrilling of holes with high aspect ratio.

Investigation of Laser Scribing Technics for Reducing Core Loss of Grain-Oriented Silicon Steels

A laser is often considered to scribe the steel surfaces after cold-rolling and annealing to reduce the energy losses associated with hysteresis and eddy currents. In order to maximize the loss reduction of this process, the laser scribing technics was investigated in details. In this work, three laser scribing parameters including pulse energy, scanning velocity and scribing spacing, which are highly related to the loss reduction, were selected for the study. A L9(34) orthogonal experiment was designed and carried out by an Nd:Yag laser marking machine. The results indicate that the subsequence of significance of the three factors on core loss reduction is as follows: pulse energy, scribing spacing and scanning velocity. And an optimized combination of parameters is obtained by range method.

Modeling of passively Q-switched Er/sup 3+//Yb/sup 3+/-codoped clad-pumped fiber lasers

We present the modeling of passively Q-switched Er/sup 3+//Yb/sup 3+/-codoped double-clad fiber lasers (EYDFL). Both two-level and three-level saturable absorbers (SAs) are used. The model is based on detailed rate equations of SAs, Er/sup 3+/, and Yb/sup 3+/ populations in the fiber, and light propagation equations including spontaneous emissions due to both Er/sup 3+/ and Yb/sup 3+/. Laser output characteristics including pulse energy, width, peak power, repetition frequency (PRF), and average power are computed as functions pump power, fiber length, single-mode/multi-mode fibers, Er/sup 3+//Yb/sup 3+/ concentrations, out-coupling reflectivity, focus area on the SA, and SA doping and length. Several transition metal-doped crystal SAs and semiconductor SA mirrors (SESAM) are considered and compared.

Laser-target interactions during pulsed laser deposition of superconducting thin films

The theoretical analysis of thermal effects induced by nanosecond laser irradiation on bulk YBa2Cu3O7 superconductor targets provides insight into the nature of the target’s ablation/evaporation characteristics during pulsed laser deposition of superconducting thin films. We have simulated the thermal history of YBa2Cu3O7 targets under intense nanosecond laser irradiation by numerically solving the one dimensional heat flow equation and taking into account the phase changes occurring at the near surface of the target. The numerical method is based on a higher-order finite difference scheme with a smaller truncation error and is not restricted by any stability criterion, thereby allowing faster convergence to the exact solution. Temperature-dependent optical and thermal properties of the irradiated material as well as the temporal variation in the laser intensity can be taken into account by this method. During planar surface evaporation of the target material, the subsurface temperatures were calculated to be higher than the surface temperatures as a result of combination of two unique effects. While the evaporating surface of the target is constantly being cooled due to the latent heat of vaporization, subsurface superheating occurs due to the finite absorption depth of the laser beam. The effects of various laser and target parameters, including pulse energy density, pulse duration, absorption coefficient, thermal conductivity, and latent heat on the transient thermal characteristics of the irradiated target, have been investigated in detail. Subsurface superheating was found to increase with decreasing absorption coefficient and thermal conductivity of the target, and with increasing energy density. The superheating may lead to subsurface nucleation and growth of the gaseous phase which expands rapidly leading to microexplosions and ‘‘volume expulsion’’ of material from the target.

Pulsed-laser evaporation technique for deposition of thin films: Physics and theoretical model.

We have studied in detail the physical phenomena involved in the interaction of high-powered nanosecond excimer-laser pulses with bulk targets resulting in evaporation, plasma formation, and subsequent deposition of thin films. A theoretical model for simulating these laser-plasma--solid interactions has been developed. In this model, the laser-generated plasma is treated as an ideal gas at high pressure and temperature, which is initially confined in small dimensions, and is suddenly allowed to expand in vacuum. The three-dimensional expansion of this plasma gives rise to the characteristic spatial thickness and compositional variations observed in laser-deposited thin films of multicomponent systems. The forward-directed nature of the laser evaporation process has been found to result from anisotropic expansion velocities of the atomic species which are controlled by the dimensions of the expanding plasma.Based on the nature of interaction of the laser beam with the target and the evaporated material, the pulsed-laser evaporation (PLE) process can be classified into three separate regimes: (i) interaction of the laser beam with the bulk target, (ii) plasma formation, heating, and initial three-dimensional isothermal expansion, and (iii) adiabatic expansion and deposition of thin films. The first two processes occur during the time interval of the laser pulse, while the last process initiates after the laser pulse terminates. Under PLE conditions, the evaporation of the target is assumed to be thermal in nature, while the plasma expansion dynamics is nonthermal as a result of interaction of the laser beam with the evaporated material. The equations of compressible gas dynamics are set up to simulate the expansion of the plasma in the last two regimes. The solution of the gas-dynamics equations shows that the expansion velocities of the plasma are related to its initial dimensions and temperature, and the atomic weight of the species. Detailed simulations analyzing the salient features of the laser-deposition process have been carried out. The effects of various beam and substrate parameters including pulse energy density, substrate-target distance, irradiated spot size, and atomic mass of the species have been theoretically analyzed. This model predicts most of the characteristic experimental features of the laser evaporation and deposition of thin films. These characteristic features include (a) the effect of pulse energy density on atomic velocities, (b) the forward-directed nature of the deposit and its dependence on energy density, (c) spatial compositional variations in multicomponent thin films as a function of energy density, (d) dependence of the atomic velocities with atomic weights of various species in multicomponent films, (e) athermal non-Maxwellian-type velocity distribution of the atomic and molecular species, and (f) thickness and compositional variations as a function of substrate-target distance and irradiated spot size.