Optimal Number Of Pulses Research Articles

Analysis of the Heat-Affected Zone and Ablation Efficiency in Terms of Burst Mode Parameters During High Power Picosecond Laser Micromachining of Metals

Abstract This paper presents a systematic study on using the burst mode ablation to limit the heat-affected zone (HAZ) while maintaining a high ablation efficiency using a high-power industrial picosecond laser with burst fluence larger than 10 J/cm2. An extended three-dimensional two-temperature model (3D-TTM) was employed to study the mechanism of the HAZ development and to predict the ablation efficiency with experimental validation. The essentiality of including the lattice heat conduction to predict accurate HAZ was discussed. The effect of the number of pulses per burst and pulse-to-pulse separation time was investigated. The optimal number of pulses per burst was obtained by using the 3D-TTM for copper and stainless steel. The 3D-TTM suggested that by using the optimal number of pulses per burst, a maximum reduction of 77% and 61% in HAZ could be achieved for copper and stainless steel respectively. And the corresponding ablation efficiency will be increased by 24% and 163% for copper and stainless steel at the same time. This study showed that burst mode laser machining at high fluence is an effective way of increasing efficiency while limiting the HAZ.

Photon energy transfer on titanium targets for laser thrusters

Abstract Using two infrared pulsed lasers systems, a picosecond solid-state Nd:YAG laser with tuneable repetition rate (400 kHz–1 MHz) working in the burst mode of a multi-pulse train and a femtosecond Ti:sapphire laser amplifier with tuneable pulse duration in the range of tens of femtoseconds up to tens of picoseconds, working in single-shot mode (TEWALASS facility from CETAL-NILPRP), we have investigated the optimal laser parameters for kinetic energy transfer to a titanium target for laser-thrust applications. In the single-pulse regime, we controlled the power density by changing both the duration and pulse energy. In the multi-pulse regime, the train’s number of pulses (burst length) and the pulse energy variation were investigated. Heat propagation and photon reflection-based models were used to simulate the obtained experimental results. In the single-pulse regime, optimal kinetic energy transfer was obtained for power densities of about 500 times the ablation threshold corresponding to the specific laser pulse duration. In multi-pulse regimes, the optimal number of pulses per train increases with the train frequency and decreases with the pulse power density. An ideal energy transfer efficiency resulting from our experiments and simulations is close to about 0.0015%.

Glass Substrate Dust Removal Using 233 fs Laser-Generated Shockwave.

Eliminating dust is gaining importance as a critical requirement in the display panel manufacturing process. The pixel resolution of display panels is increasing rapidly, which means that even small dust particles on the order of a few micrometers can affect them. Conventional surface cleaning methods such as ultrasonic cleaning (USC), CO2 cleaning, and wet cleaning may not be sufficiently efficient, economical, or environment friendly. In this study, a laser shockwave cleaning (LSC) method with a 233 fs pulsed laser was developed, which is different from the laser ablation cleaning method. To minimize thermal damage to the glass substrate, the effect of the number of pulses and the gap distance between the focused laser beam and the glass substrate were studied. The optimum number of pulses and gap distance to prevent damage to the glass substrate was inferred as 500 and 20 μm, respectively. With the optimal pulse number and gap distance, cleaning efficiency was tested at a 95% removal ratio regardless of the density of the particles. The effective cleaning area was measured using the removal ratio map and compared with the theoretical value.

Characteristics of Non-Ablative Resurfacing of Soft Tissues by Repetitive Er:YAG Laser Pulse Irradiation.

Background and ObjectivesRecently, several minimally invasive gynecological, ENT and esthetic procedures have been introduced that are based on delivering “smooth” sequences of Er:YAG laser pulses to cutaneous or mucosal tissue at moderate cumulative fluences that are not only below the ablation threshold but typically also do not require local anesthesia. To explain the observed clinical results using “smooth‐resurfacing,” it has been suggested that in addition to the direct heat injury to deeper‐lying connective tissues, there is an additional mechanism based on indirect triggering of tissue regeneration through short‐exposure, intense heat shocking of epithelia. The goal of this study is to improve understanding of the complex dynamics of the exposure of tissues to a series of short Er:YAG laser pulses, during which the thermal exposure times transition from extremely short to long durations.Study Design/Materials and MethodsA physical model of laser‐tissue interaction was used to calculate the temperature evolution at the irradiated surface and deeper within the tissue, in combination with a chemical model of tissue response based on the recently introduced variable heat shock (VHS) model, which assumes that the tissue damage represents a combined effect of two limiting Arrhenius′ processes, defining cell viability at extremely long and short exposure times. Superficial tissue temperature evolution was measured during smooth‐resurfacing of cutaneous and mucosal tissue, and compared with the model. Two modalities of non‐ablative resurfacing were explored: a standard “sub‐resurfacing” modality with cumulative fluences near the ablation threshold, and the “smooth‐resurfacing” modality with fluences below the patient′s pain threshold. An exemplary skin tightening clinical situation was explored by measuring pain tolerance threshold fluences for treatments on abdominal skin with and without topical anesthesia. The obtained temperature data and pain thresholds were then used to study the influence of Er:YAG laser sequence parameters on the superficial (triggering) and deep (coagulative) tissue response.ResultsThe simulations show that for the sub‐resurfacing modality, the parameter range where no excessive damage to the tissue will occur is very narrow. On the other hand, using pain tolerance as an indicator, the smooth‐resurfacing treatments can be performed more safely and without sacrificing the treatment efficacy. Two preferred smooth‐resurfacing treatment modalities were identified. One involves using optimally long pulse sequence durations (≈1–3 seconds) with an optimal number of pulses (N ≈ 10–30), resulting in a maximal short‐exposure superficial tissue response and moderate coagulation depths. And for deeper coagulation, without significant superficial heat shocking, very long pulse sequences (>5 seconds) with a large number of delivered pulses are to be used in combination with topical anesthesia.ConclusionsA comparison of the simulations with the established smooth‐resurfacing clinical protocols in gynecology, ENT, and esthetics suggests that, through clinical experience, the clinical protocols have been optimized for the maximal superficial heat shock triggering effect. Further research is needed to gain a better understanding of the proposed role of heat shock triggering in the clinically observed regeneration of cutaneous, vaginal, and oral tissues following Er:YAG laser smooth‐resurfacing. Lasers Surg. Med. © 2021 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC.

Simulation of Square Cluster Planting

Introduction. For cultivated crops, the optimal form of spacing is square form, which is provided by the square cluster method of planting. Currently, due to the high metal consumption and low productivity, this method of planting has been replaced with a single-seed planting one. But this does not solve the problem of rational distribution of seeds in the field, so the problem of plant spacing with the use of the optimal square form of spacing is relevant. The aim of the study is to develop and analyze a simulation model of square cluster planting based on an algorithm for controlling the executive mechanisms of the seeder sections using devices for local coordination of the seeding apparatus. Materials and Methods. A programmable square cluster planting using local coordination of the seeding apparatus and an algorithm for its realization are considered. The article describes the construction of a simulation model of sowing planting in Simulink Matlab with justification of its elements. The seed spreading in furrows and the seeder variable speed are taken into account. The number of pulses per revolution of the encoder shaft is theoretically justified. Results. The graphs of the distance traveled, positions coordinates of the flap opening and control signals depending on the time are constructed. The analysis of the encoder settings is carried out. When varied the plant spacing and the coordinates of the first flap opening, the dimension of the last seed cluster changes in the range from –2.6 ∙ 10–3 to 2.7 ∙ 10–3 m. With the increase in the seeder speed from 1.5 to 3.0 m/s, the mathematical expectation of the seed cluster dimensions increase from 0.054 to 0.218 m, and the coefficient of variation decreases from 61.2 to 15.0%. Discussion and Conclusion. The analysis of the simulation model of the square cluster planting showed that the algorithm for controlling executive mechanisms together with the local coordination system works adequately and provides high precision of placing seed clusters in the field. The dependences of the optimal number of pulses per an encoder shaft revolution on the specified seed spacing and radius of the track measuring wheel are determined. It was determined that the maximum dimension of the last seed cluster does not exceed 2.7 mm per 1 000 m (for x = 0.3 m and t = 0.7 m). It was found that the precision of the distribution of seed clusters in the field is determined more by the seeder speed than by the settings of the measuring device.

Motor Evoked Potentials Double Train Stimulation: Optimal Number of Pulses per Train.

In neurophysiologic intraoperative monitoring, double train transcranial electrical stimulation (dt-TES) for motor evoked potentials (MEP) consists of an initial, facilitating train of stimuli followed by a second, testing, train. The optimal number of pulses per train has not been determined. The authors wanted to determine the optimal combination of pulses per train that produced the highest MEP amplitude. Dt-TES of 4 + 4, 2 + 7, and 7 + 2 pulses were attempted in 20 patients and compared with single train TES of nine pulses. Latencies of the MEP responses were also compared. Additionally, statistical comparisons were made of the differences between the amplitude and latency measurements within the patients. The mean age of the patients was 44.3 years (range, 9-84 years). Dt-TES of 2 + 7 pulses resulted in significantly higher mean amplitudes than dt-TES of 4 + 4 and 7 + 2 pulses and single train TES of nine pulses ( p < 0.001). The MEP latency with dt-TES of 2 + 7 pulses was longer than the latencies of single train TES of nine pulses and dt-TES of 4 + 4 and 7 + 2 pulses. Asymmetric dt-TES with 2 + 7 pulses improved MEP amplitudes. This type of stimulation may be preferable to single train TES and dt-TES with symmetric pulse trains.

Effect of multi-pulses train on the thermomechanical response of a metal thin film

ABSTRACTUltrafast thermoelasticity based on hyperbolic two-step heat conduction model with electron-phonon interaction was applied to investigate the thermomechanical coupling responses of an immense homogeneous, isotropic gold film, which was irradiated by various ultrashort laser pulse trains. The solution to the problem was obtained by solving finite element governing equations. For the same energy injection, a new micromachining technique using laser pulse trains can offer certain advantages compared with a single laser pulse micromachining, such that the laser pulse train is provided with the advantages of long and short laser pulses. The effects of the pulse number and the pulse separation times for a laser pulse train on ultrafast thermomechanical coupling responses, i.e., the temperature, displacement as well as stress, are presented graphically and analyzed. It was found from the numerical results that the expected machining results (or thermomechanical responses) may be obtained by using pulse train technology with optimal pulse number and pulse separation time.

골육세포 성장 촉진을 위한 스마트 써피스 텍스처링 임플란트 스템 제작 기술

To enhance biocompatibility between the orthopedic implant stem and obsteoblast cells, boneforming cells, micro-size holes are patterned in Ti plate surface. Initially, the house built laser power stabilization system is applied to the laser micro patterning machine to convince repeatable result. Various pulse widths are irradiated Ti plate and relationship between diameters of patterned holes and pulsed width is derived. Effect of multi pulse is observed and optimal pulse number is considered to avoid heat affected zone. After MG-63 osbeoblast cells are cultured, micro patterned Ti plates are compared with control plates. In SEM image, cells are well aligned and aggregation is observed in both 60, and 100μm patterned plates. Finally, free form surface stem model is prepared to test micro hole patterning.

Formulation of the modified akaike information criterion (AIC) for a one‐dimensional multipulse model and its application to image coding

AbstractIn recent years, attention has been given to coding based on the structurally extracted component and the three dimensional object model. However, it has a problem in that the content of the processing and the required model are fairly complex compared to the conventional waveform coding.From such a viewpoint, the authors considered the one‐dimensionalmultipulse model, which was proposed as an analysis/synthesis technique for speech, and have been investigating the method using the model which can easily extract the structure of the image and provide the coding.In this paper, the multipulse model is regarded as a stochastic model. A method is proposed, where the number of pulses required to represent the features of the image is determined automatically using Akaike's information criterion and a similar criterion (called modified AIC).As the first step, the modified AIC for the multipulse model is derived, and the sequential computation procedure is shown. Then the relation between the penalty coefficient of the modified AIC and the optimal number of pulses is described, and a method is shown based on that result where the traditional information criterion is utilized selectively based on the constraint for the compression ratio of the number of pulses.Finally, the modified AIC for the multipulse model is applied to the hierarchical coding from the two‐tone image to the gray‐level image, and the usefulness is demonstrated. It is expected that the proposed method will be applied to the image coding, image feature extraction and speech feature extraction.