Influence Of Pulse Duration Research Articles

Investigating the influence of pulse duration in burst mode ablation of stainless steel

Using ultrashort laser pulses in a megahertz burst to create a smoothing effect in the ablation of stainless steel for various industrial applications.

Influence of pulse duration on the process of laser marking of CT80 carbon tool steel products

Depending on the processing of a particular material, the laser marking process must meet certain requirements. A certain laser peak intensity or fluency must be reached on the treatment surface above which the laser ablation process starts. Some experimental studies have shown that this particular marking threshold is related to many other parameters characterizing the laser source. This requires the realization of an appropriate combination of peak power or pulse energy and the radius of the beam in focus, the frequency of the laser pulses as well as the pulse duration. Achieving high resolution in the marking process requires optimal focusing, and this in turn is associated with the presence of high quality generated and propagated laser radiation. The study concerns the process of laser marking of CT80 carbon tool steel products with wide application in industry. Numerical experiments are performed with specialized software TEMPERATURFELD3D to obtain two-dimensional and three-dimensional temperature fields in the laser impact zone. The influence of the duration of the pulses of fibre laser on the process is investigated. Graphs of the dependence of normalized temperature on time and depth for pulse duration on 10 ns, 100 ns and 1 μs are discussed.

Influence of Pulse Duration of Intense Transcutaneous Electrical Nerve Stimulation on Pressure Pain Thresholds

Influence of Pulse Duration of Intense Transcutaneous Electrical Nerve Stimulation on Pressure Pain Thresholds

Two-photon microperimetry with picosecond pulses.

Two-photon vision is a phenomenon associated with the perception of short pulses of near-infrared radiation (900-1200 nm) as a visible light. It is caused by the nonlinear process of two-photon absorption by visual pigments. Here we present results showing the influence of pulse duration and repetition rate of short pulsed lasers on the visual threshold. We compared two-photon sensitivity maps of the retina obtained for subjects with normal vision using a cost-effective fiber laser (λc = 1028.4 nm, τp = 12.2 ps, Frep = 19.17 MHz) and a solid-state laser (λc = 1043.3 nm, τp = 0.253 ps, Frep = 62.65 MHz). We have shown that in accordance with the description of two-photon absorption, the average optical power required for two-photon vision for a fiber laser is 4 times greater than that for a solid-state laser. Mean sensitivity measured for the first one is 5.9 ± 2.8 dB lower than for the second but still 17 dB away from the safety limit, confirming that picosecond light sources can be successfully applied in microperimetry. This development would dramatically reduce the cost and complexity of future clinical devices.

Rapid laser nanomanufacturing and direct patterning of 2D materials on flexible substrates—2DFlex

Direct synthesis, large-scale integration, and patterning of two-dimensional (2D) quantum materials (e.g. MoS2, WSe2) on flexible and transparent substrates are of high interest for flexible and conformal device applications. However, the growth temperatures (e.g. 850 °C) of the emerging 2D materials in the common gas-phase synthesis methods are well beyond the tolerances limit of flexible substrates, such as polydimethylsiloxane (PDMS). In addition, random nucleation and growth process in most growth systems limits the predicted integration and patterning freedoms. Here, we report a rapid direct laser crystallization and mask-free large-scale patterning of MoS2 and WSe2 crystals on PDMS substrates. A thin layer of stoichiometric amorphous 2D film is first laser-deposited via pulsed laser deposition (PLD) system onto the flexible substrates followed by a controlled crystallization and direct writing process using a tunable nanosecond laser (1064 nm). The influences of pulse duration, number of pulses, and the thickness of the deposited amorphous 2D layer on the crystallization of 2D materials are discussed. Optical spectroscopy and electrical characterizations are performed to confirm the quality of crystallized 2D materials on flexible substrates. This novel method opens up a new opportunity for the crystallization of complex patterns directly from computer-aided design models for the future 2D materials-based wearable, transparent, and flexible devices.

Influence of pulse duration and repetition rate on mid-infrared cascaded supercontinuum.

We experimentally investigate the influence of varying pulse parameters on the spectral broadening, power spectral density, and relative intensity noise of mid-infrared (mid-IR) in-amplifier cascaded supercontinuum generation (SCG) by varying the pulse duration (35 ps, 1 ns, 3 ns) and repetition rate (100, 500, 1000 kHz). The system is characterized at the output of the erbium-ytterbium-doped in-amplifier SCG stage, the thulium/germanium power redistribution stage, and the passive ZBLAN fiber stage. In doing so, we demonstrate that the output of the later stages depends critically on the in-amplifier stage, and relate this to the onset of modulation instability.

Fundamental investigations of ultrashort pulsed laser ablation on stainless steel and cemented tungsten carbide

An ultrashort pulse laser, capable of varying the pulse duration from 0.2 ps up to 10 ps, is used to study the ablation characteristics of stainless steel and cemented tungsten carbide. In addition to the influence of pulse duration, the number of pulses and the wavelength are examined for their influence on the ablation process. By determining the ablation diameter of generated cavities, the ablation threshold of the materials is calculated as a function of the number of pulses, the pulse duration, and the wavelength. The experimentally determined ablation thresholds tend to agree with calculated values. Due to the incubation effect, the ablation threshold decreases with increasing the number of pulses. In this context, the incubation factor (0.81@1030 nm and 0.80@515 nm for stainless steel, 0.90@1030 nm and 0.77@515 nm for cemented tungsten carbide) for the investigated materials is determined. On the basis of the measured ablated volume, the effective penetration depth (a reduction in a range from about 12 nm and 15 nm to 6 nm for stainless steel and in a range from 22 nm and 32 nm to 11 nm and 13 nm for cemented tungsten carbide by increasing the pulse duration from 0.2 ps to 10 ps) of the energy is calculated and it is proven that in the femtosecond regime the penetration depth increases compared with the picosecond regime. In consequence, the efficiency of the ablation process is increased by using shorter laser pulses.

High-energy femtosecond laser system based on a fiber laser seeder, Yb:YAG single crystal fiber and chirped volume Bragg grating

A high-energy chirped pulse amplification system based on a Yb doped fiber seeder, two-stage single crystal fiber (SCF) amplifier with a simple single-pass structure is demonstrated in this work. An amplified power of 52.2 W with a beam quality of less than 1.3 at 200 kHz is obtained, to our best knowledge, this is the highest power obtained with a single-pass amplification structure of the SCF with the energy of hundreds of microjoules. An excellent power stability of 0.32% is obtained. Dispersion between the chirped fiber Bragg grating (CFBG) stretcher and the chirped volume Bragg grating compressor is matched via the use of a self-made temperature tuning device of CFBG. As a result, a pulse duration of 740 fs and a compressed power of 31.4 W are obtained at a repetition rate of 200 kHz. In order to assess the influence of pulse duration induced by the nonlinearity during the amplification and increase the output pulse energy,the repetition rate of the self-made fiber seeder is changed to 100 kHz. A compressed power of 28.4 W and a pulse width of 858 fs are obtained, corresponding to a pulse energy of 284 µJ and a peak power of 331 MW. This compact and high-energy femtosecond laser system will find various applications in both scientific research and industrial implementation.

Influence of pulse duration and pulse frequency on micro-roughness for laser micro polishing (LµP) of stainless steel AISI 410

Press plates for decorative laminates are often made from AISI410 and typically need a surface finish created by polishing. A new manufacturing process that can overcome disadvantages from conventional polishing processes is laser micro-polishing (LµP). Therefore, this experimental investigation focuses on the effect of LµP on the micro-roughness in the nanometer range for stainless steel AISI410. This study closes a gap regarding investigations for LµP with pulse durations from 10 ns to 220 ns and pulse frequencies from 20 kHz to 240 kHz using a commercially available 35 W fiber laser. The feasibility for LµP on AISI410 in terms of achieved micro-roughness and avoidance of surface defects was successfully demonstrated. A significant reduction of surface roughness was achieved using pulse durations as short as 10 ns and pulse frequencies as high as 240 kHz. In addition, indications for a fundamental change of the process from a discrete, pulsed process to a continuous remelting process were observed and an empirical estimation for the prediction of this change was derived. Furthermore, spatially resolved laser polishing was demonstrated on textured press plates. With area rates of up to several square meters per hour within reach, LµP on AISI410 stands ready for industrial implementation.

Optical rectification of ultrafast Yb lasers: pushing power and bandwidth of terahertz generation in GaP

We demonstrate broadband high-power terahertz (THz) generation at megahertz repetition rates by optical rectification in GaP driven by an ultrafast Yb-based thin-disk laser (TDL) oscillator. We investigate the influence of pulse duration in the range of 50–220 fs and thickness of the GaP crystal on the THz generation. Optimization of these parameters with respect to the broadest spectral bandwidth yields a gap-less THz spectrum extending to nearly 7 THz. We further tailor the driving laser and the THz generation parameters for the highest average power, demonstrating 0.3 mW THz radiation with a spectrum extending to 5 THz. This was achieved using a 0.5 mm thick GaP crystal pumped with a 95 fs, 20 W TDL, operating at 48 MHz repetition rate. We also provide a simple method to estimate the THz spectrum, which can be used for design and optimization of similar THz systems.

Selective rear-side ablation of aluminum thin layers with ultrashort-pulsed laser radiation

In recent years, several applications for laser ablation of thin metal layers from the fused silica substrate side have been studied. The rear-side ablation is a highly effective ablation method for thin layer structuring and reveals a high structuring quality. Therefore, the present work dealt with the selective rear-side ablation of thin aluminum layers (10–50 nm) on fused silica with ultrashort-pulsed laser radiation (λ = 1028 nm, $$ \tau_{\text{H}} $$ = 0.2–10 ps and w0,86 = 15.2 µm). The influences of pulse duration and layer thickness on the ablation thresholds as well as the incubation coefficients were determined. For layer thicknesses of 30 and 50 nm, a decrease of the ablation threshold with increasing pulse duration was determined. Whereas, the ablation threshold remained constant for layer thicknesses of 10 and 20 nm. Different morphologies were observed depending on the process parameters. The rear-side ablation of aluminum proceeded over the melting phase and no lift-off process had taken place. In addition to experimental investigations, calculations were carried out to determine the theoretical threshold fluences. The theoretical values were compared to experimental data. With the help of these investigations, the quality of the structuring of aluminum layers can be improved.

Impulse breakdown of liquid water - influence of pulse duration and gap distance

In this study, the impulse breakdown of conductive water (350 μS/cm) was carried out under 25~1500 μs pulses and with a gap distance of 0.5~100 mm. The influence of pulse duration, gap distance and voltage polarity on the breakdown characteristics are shown. Martin's equation and streamer linear propagation (SLP) model for breakdown voltage calculation are compared, and their application conditions are indicated. The results show the pulse duration and the gap distance on the breakdown characteristics are opposite; however, their influence on voltage polarity are similar. Martin's equation is only appropriate for short impulse breakdown (nanosecond) while the SLP model is shown to be suitable for long impulse breakdown (microsecond or longer).

On the pulsed laser ablation of polycrystalline cubic boron nitride—Influence of pulse duration and material properties on ablation characteristics

Polycrystalline cubic boron nitride (PCBN) is widely used in industry as a cutting tool material for the machining of hardened steels, cast iron, or nickel-based super alloys. For the generation of geometrical features on such cutting tools, laser ablation is a novel and promising technology, which offers wear-free processing, high automation potential, and geometrical flexibility. In this study, the ablation mechanisms are experimentally investigated for a wide range of laser pulse durations (fs–ns regime), and the effects on ablation depth, ablation efficiency, and surface roughness are investigated. It is shown that melting and recrystallization of binder material when processing with nanosecond pulse duration leads to a reduction of the ablation efficiency and reduced surface quality. These defects can be avoided by using a shorter pulse duration (picosecond and femtosecond). The highest ablation efficiency is achieved for femtosecond laser ablation. Moreover, fs-laser processing shows beneficial behavior in the ablation of coarse-grained PCBN grades, where grain excavation due to binder removal is prevented and the resulting surface roughness is significantly decreased compared to ns-laser processing.

Effect of different hardness and melting point of the metallic surfaces on structural and optical properties of synthesized nanoparticles

The relations between macroscopic and microscopic characteristics of materials are of utmost importance for synthesis of multi-atomic structures with advanced properties. We analyze the influence of pulse duration, pulse energy and temperature of liquid on the process of formation of nanoparticles (NPs) of the metals (In, Sn, Zn and W) with different hardness and melting temperature by laser ablation in liquid environment. Composition, morphology dynamics and properties of nanoparticle suspensions are studied using TEM analysis and Z-scan technique. The nonlinear optical properties of NPs are analyzed at 800 and 400 nm using 60 fs and 200 ps pulses. We show that pulse energy have little influence on the formation, morphology and size of NPs during ablation of low hardness and melting point metal (In). However, pulse duration plays a very important role during the formation of NPs, especially the ultra-short pulse has a positive effect on the preparation of NPs with smaller particle size. In addition, the temperature of liquid environment influences the formation of NPs and their nonlinear optical properties.

Investigation of laser pulsing parameters’ importance in Er:YAG laser skin ablation: a theoretical study conducted via newly developed thermo-mechanical ablation model

Objective: Importance of laser pulsing parameters and tissue’s mechanical properties in the Er:YAG laser skin-tissue ablation is not adequately understood. The goal here was to develop a computational model that incorporates skin tissue’s mechanical properties to investigate the influence of Er:YAG laser pulsing parameters on tissue ablation and coagulation.Methods: Tissue’s mechanical properties were incorporated by modeling ablation as a tissue water vaporization occurring under elevated pressures that depend on tissue’s stress–strain relationships. Tissue deformation was assumed unidirectional; therefore, a one-dimensional model was utilized. Analytical solution and experimental results were used to verify and validate the model. Then, influence of pulse duration (10 µs–2 ms) and fluence (0–30 J cm−2) on coagulation depth and ablation efficiency was explored.Results: Verification and validation results suggested that the model is acceptably accurate. Minimal effect of pulse duration on coagulation depth was predicted at sub-ablative conditions. At those conditions, coagulation depth increased asymptotically to ∼90 µm with increasing pulse fluence. At ablative conditions, coagulation depth decreased asymptotically to 22–28 µm with increasing pulse irradiance. Ablation efficiency plateaued at high pulse fluences and long pulse durations. Mechanical properties were important as about 50% increase in coagulation depth and 25% decrease in ablation efficiency were predicted when considering the high strain-rate loading effect in comparison with quasi-static loading.Conclusions: Proper tuning of Er:YAG laser pulsing parameters can substantially improve its therapeutic outcomes. The effect of these parameters varies and depends on whether the laser-tissue conditions are ablative or sub-ablative.

Influence of Pulse Duration on High-Precision Manufacturing of 3D Geometries

Influence of Pulse Duration on High-Precision Manufacturing of 3D Geometries

Effects of pulse durations and environments on femtosecond laser ablation of stainless steel

The influence of pulse durations (35fs and 260 fs) and environments (air and vacuum) on the laser-induced damage thresholds (LIDTs) and ablation rates of 304 stainless steel were studied. Two distinct ablation regimes were obtained from the ablation rate curves. At low fluence regime, the ablation rates were similar in spite of the differences of pulse durations and experiment environments. At high fluence regime, the ablation rates of 35 fs pulse duration in vacuum were obviously higher than others. The ablation craters showed smooth edges, moth-eye such as structures, and laser-induced periodic surface structures (LIPSSs). At a fixed fluence, the periods of LIPSSs decreased monotonously in their mean spatial period between ~ 700 nm (5 pulses) and 540 nm (200 pulses) with the increase of pulse numbers in air with 35 fs pulse duration. The formation mechanisms of moth-eye like structures and LIPSSs were also discussed.

High efficiency plasma treatment of water contaminated with organic compounds. Study of the degradation of ibuprofen

The degradation of ibuprofen in water by nonthermal plasma is studied using a pulsed corona discharge above liquid, generated in oxygen. The influence of pulse duration (50–430 ns FWHM) on removal efficiency and on mineralization was investigated. Complete removal of the target compound was achieved within 15–20 min plasma treatment and the mineralization degree reached 76% after 60 min. The energy efficiency was greatly enhanced by reducing pulse length: 20.2 g kWh−1 was obtained for 50 ns pulses at 90% IBP removal, more than one order of magnitude higher than the value for the longest pulses. Higher initial concentration of the target compound led to further improvement of the energy yield, but required more time to complete the degradation process.

Influence of Pulse Duration on Effective Energy on Material Removal in Micro-processing of Mild Steel by Several Hundred Nanoseconds Pulsed Laser

Influence of Pulse Duration on Effective Energy on Material Removal in Micro-processing of Mild Steel by Several Hundred Nanoseconds Pulsed Laser

Electrical Discharge Machining of Polycrystalline Diamond Using Copper Electrode - Finishing Condition

Research on machining process of Polycrystalline Diamond (PCD) is becoming important as the material was believed suitable to be used for cutting tools of advanced aeronautical structure. Electrical Discharge Machining (EDM) was regarded as the suitable method to machine PCD due its noncontact process nature. The objective of this research is to determine the influence of several EDM parameter such as sparking current, pulse duration, and pulse interval to the material removal rate and surface roughness of the machined PCD. Instead of significantly influenced the material removal rate, the sparking current was also highly influenced tha surface roughness. Highest material removal rate of approximately 0.005mm3/s was recorded by the EDM process with the highest current used of 5A, and lowest pulse interval of 1µs. The influence of pulse duration is not clearly seen at the lowest pulse interval used. On the other hand, 0.4pm was the lowest surface roughness value obtained in this research indicated by the highest sparking current, highest sparking duration and lowest sparking interval of 5A, 1μs and 1μs respectively.