Residual heat generated during laser processing of CFRP with picosecond laser pulses

2018 ◽  
Vol 7 (3) ◽  
pp. 157-163
Author(s):  
Christian Freitag ◽  
Leon Pauly ◽  
Daniel J. Förster ◽  
Margit Wiedenmann ◽  
Rudolf Weber ◽  
...  
Keyword(s):  
Laser Pulse ◽  
Heat Affected Zone ◽  
Laser Processing ◽  
Picosecond Laser ◽  
Theoretical Models ◽  
Laser Pulses ◽  
Groove Depth ◽  
Interaction Zone ◽  
Heat Accumulation ◽  
Residual Heat

Abstract One of the major reasons for the formation of a heat-affected zone during laser processing of carbon fiber-reinforced plastics (CFRP) with repetitive picosecond (ps) laser pulses is heat accumulation. A fraction of every laser pulse is left as what we termed residual heat in the material also after the completed ablation process and leads to a gradual temperature increase in the processed workpiece. If the time between two consecutive pulses is too short to allow for a sufficient cooling of the material in the interaction zone, the resulting temperature can finally exceed a critical temperature and lead to the formation of a heat-affected zone. This accumulation effect depends on the amount of energy per laser pulse that is left in the material as residual heat. Which fraction of the incident pulse energy is left as residual heat in the workpiece depends on the laser and process parameters, the material properties, and the geometry of the interaction zone, but the influence of the individual quantities at the present state of knowledge is not known precisely due to the lack of comprehensive theoretical models. With the present study, we, therefore, experimentally determined the amount of residual heat by means of calorimetry. We investigated the dependence of the residual heat on the fluence, the pulse overlap, and the depth of laser-generated grooves in CRFP. As expected, the residual heat was found to increase with increasing groove depth. This increase occurs due to an indirect heating of the kerf walls by the ablation plasma and the change in the absorbed laser fluence caused by the altered geometry of the generated structures.

Laser processing of GaN-based LEDs with ultraviolet picosecond laser pulses

2012 ◽  
Author(s):  
Rüdiger Moser ◽  
Michael Kunzer ◽  
Christian Goßler ◽  
Ralf Schmidt ◽  
Klaus Köhler ◽  
...  
Keyword(s):  
Laser Processing ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Picosecond Laser Pulses

Laser processing of gallium nitride–based light-emitting diodes with ultraviolet picosecond laser pulses

2012 ◽  
Vol 51 (11) ◽  
pp. 114301 ◽  
Author(s):  
Rüdiger Moser ◽  
Michael Kunzer ◽  
Christian Goßler ◽  
Klaus Köhler ◽  
Wilfried Pletschen ◽  
...  
Keyword(s):  
Gallium Nitride ◽  
Laser Processing ◽  
Light Emitting Diodes ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Light Emitting ◽  
Picosecond Laser Pulses

scholarly journals Динамика спинорной экситон-поляритонной системы в латерально сжатых GaAs микрорезонаторах при резонансном фотовозбуждении

2018 ◽  
Vol 60 (8) ◽  
pp. 1567
Author(s):  
А.А. Деменев ◽  
Н.А. Гиппиус ◽  
В.Д. Кулаковский
Keyword(s):  
Laser Pulse ◽  
Spatial Coherence ◽  
Picosecond Laser ◽  
Threshold Value ◽  
Laser Pulses ◽  
Josephson Effects ◽  
High Q ◽  
Wide Range ◽  
Linearly Polarized ◽  
Polariton Branch

AbstractThe evolution of the spatial coherence and the polarization has been studied in a freely decaying polariton condensate that is resonantly excited by linearly polarized picosecond laser pulses at the lower and upper sublevels of the lower polariton branch in a high-Q GaAs-based microcavity with a reduced lateral symmetry without excitation of the exciton reservoir. It is found that the condensate inherits the coherence of the exciting laser pulse at both sublevels in a wide range of excitation densities and retains it for several dozen picoseconds. The linear polarization of the photoexcited condensate is retained only in the condensate at the lower sublevel. The linearly polarized condensate excited at the upper sublevel loses its stability at the excitation densities higher a threshold value: it enters a regime of internal Josephson oscillations with strongly oscillating circular and diagonal linear degrees of polarization. The polariton–polariton interaction leads to the nonlinear Josephson effects at high condensate densities. All the effects are well described in terms of the spinor Gross–Pitaevskii equations. The cause of the polarization instability of the condensate is shown to be the spin anisotropy of the polariton–polariton interaction.

Self-Guided Intense Laser Pulse Propagation in Air

2001 ◽  
Vol 6 (1) ◽  
pp. 21-26
Author(s):  
R. Danielius ◽  
D. Mikalauskas ◽  
A. Dubietis ◽  
A. Piskarskas
Keyword(s):  
Laser Pulse ◽  
Laser Beam ◽  
Phase Modulation ◽  
Large Scale ◽  
Pulse Propagation ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Intense Laser ◽  
Intense Laser Pulse ◽  
Self Phase Modulation

We report on observation of self-guiding of picosecond laser pulses in air that produces large-scale self-phase modulation. The converging picosecond laser beam produced a confined filament over 3 m of propagation with the whitelight spectrum.

scholarly journals Towards optimization of femtosecond laser pulse nanostructuring of targets for high-intensity laser experiments in vacuum

2021 ◽  
Vol 127 (7) ◽  
Author(s):  
A. Andreev ◽  
J. Imgrunt ◽  
V. Braun ◽  
I. Dittmar ◽  
U. Teubner
Keyword(s):  
Laser Pulse ◽  
Femtosecond Laser ◽  
High Intensity ◽  
Extreme Ultraviolet ◽  
Theoretical Models ◽  
Laser Pulses ◽  
High Energy ◽  
Femtosecond Laser Pulses ◽  
Laser Development ◽  
Laser Experiments

AbstractThe interaction of intense femtosecond laser pulses with solid targets is a topic that has attracted a large amount of interest in science and applications. For many of the related experiments a large energy deposition or absorption as well as an efficient coupling to extreme ultraviolet (XUV), X-ray photon generation, and/or high energy particles is important. Here, much progress has been made in laser development and in experimental schemes, etc. However, regarding the improvement of the target itself, namely its geometry and surface, only limited improvements have been reported. The present paper investigates the formation of laser-induced periodic surface structures (LIPSS or ripples) on polished thick copper targets by femtosecond Ti:sapphire laser pulses. In particular, the dependence of the ripple period and ripple height has been investigated for different fluences and as a function of the number of laser shots on the same surface position. The experimental results and the formation of ripple mechanisms on metal surfaces in vacuum by femtosecond laser pulses have been analysed and the parameters of the experimentally observed “gratings” interpreted on base of theoretical models. The results have been specifically related to improve high-intensity femtosecond-laser matter interaction experiments with the goal of an enhanced particle emission (photons and high energy electrons and protons, respectively). In those experiments the presently investigated nanostructures could be generated easily in situ by multiple pre-pulses irradiated prior to a subsequent much more intense main laser pulse.

scholarly journals Sequences of Sub-Microsecond Laser Pulses for Material Processing: Modeling of Coupled Gas Dynamics and Heat Transfer

2019 ◽  
Vol 9 (22) ◽  
pp. 4785
Author(s):  
Gusarov ◽  
Kovalev
Keyword(s):  
Heat Transfer ◽  
Laser Radiation ◽  
Laser Processing ◽  
Gas Dynamics ◽  
Optical Breakdown ◽  
Single Pulse ◽  
Laser Pulses ◽  
High Repetition Rate ◽  
Heat Accumulation ◽  
Pulse Separation

Multipulse laser processing of materials is promising because of the additional possibilities to control the thickness of the treated and the heat-affected zones and the energy efficiency. To study the physics of mutual interaction of pulses at high repetition rate, a model is proposed where heat transfer in the target and gas-dynamics of vapor and ambient gas are coupled by the gas-dynamic boundary conditions of evaporation/condensation. Numerical calculations are accomplished for a substrate of an austenitic steel subjected to a 300 ns single pulse of CO2 laser and a sequence of the similar pulses with lower intensity and 10 μs inter-pulse separation assuring approximately the same thermal impact on the target. It is revealed that the pulses of the sequence interact due to heat accumulation in the target but they cannot interact through the gas phase. Evaporation is considerably more intensive at the single-pulse processing. The vapor is slightly ionized and absorbs the infrared laser radiation by inverse bremsstrahlung. The estimated absorption coefficient and the optical thickness of the vapor domain are considerably greater for the single-pulse regime. The absorption initiates optical breakdown and the ignition of plasma shielding the target from laser radiation. The multipulse laser processing can be applied to avoid plasma ignition.

scholarly journals Extending Single Cell Bioprinting from Femtosecond to Picosecond Laser Pulse Durations

Micromachines ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1172
Author(s):  
Jun Zhang ◽  
Yasemin Geiger ◽  
Florian Sotier ◽  
Sasa Djordjevic ◽  
Denitsa Docheva ◽  
...  
Keyword(s):  
Laser Pulse ◽  
Single Cell ◽  
Pulse Duration ◽  
Cavitation Bubble ◽  
Mammalian Cells ◽  
Single Cells ◽  
Picosecond Laser ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Cost Efficient

Femtosecond laser pulses have been successfully used for film-free single-cell bioprinting, enabling precise and efficient selection and positioning of individual mammalian cells from a complex cell mixture (based on morphology or fluorescence) onto a 2D target substrate or a 3D pre-processed scaffold. In order to evaluate the effects of higher pulse durations on the bioprinting process, we investigated cavitation bubble and jet dynamics in the femto- and picosecond regime. By increasing the laser pulse duration from 600 fs to 14.1 ps, less energy is deposited in the hydrogel for the cavitation bubble expansion, resulting in less kinetic energy for the jet propagation with a slower jet velocity. Under appropriate conditions, single cells can be reliably transferred with a cell survival rate after transfer above 95% through the entire pulse duration range. More cost efficient and compact laser sources with pulse durations in the picosecond range could be used for film-free bioprinting and single-cell transfer.

scholarly journals Alterations in the microhardness of a titanium alloy affected to a series of nanosecond laser pulses

2019 ◽  
Vol 298 ◽  
pp. 00051 ◽  
Author(s):  
Ivan Ushakov ◽  
Yuri Simonov
Keyword(s):  
Titanium Alloy ◽  
Laser Pulse ◽  
Laser Processing ◽  
Crack Formation ◽  
Laser Pulses ◽  
Hardened Layer ◽  
Material Surface ◽  
Nanosecond Laser ◽  
Plastic Properties ◽  
Geometrical Pattern

The alterations in the microhardness of a titanium alloy Ti85.85Al6.5Zr4Sn2Nb1Mo0.5Si0.15 subjected to laser treatment were investigated. Laser processing consists of a series of pulses with durations 20 ns. We used various methods of laser processing, which differed in power density, wavelength, geometrical pattern of irradiation and so on. The dependences of the microhardness on the load on the indenter were found. The laser processing modes providing the increased microhardness are determined. The investigations were carried out at loads from 0.49 N to 4.9 N, with maximum indentation depth of the Vickers pyramid up to 12 μm. Vickers microhardness can be increased by 20 – 40 %. At the same time, the plastic properties of the hardened layer are improved. The probability of crack formation during indentation of the initial alloy increased with a load on the indenter and reached 0.52 for a load of 4.9 N. In two of the treated areas of the three presented, crack formation was not recorded at any load. The mechanisms of hardening of the material surface layer under the influence of a laser pulse are discussed. Using the methods of computational mathematics, the character of sample heating under the influence of a single laser pulse is determined. The perspectives for the development of the proposed processing method are permitting to obtain the optimal mechanical properties of the hardened layer are discussed.

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