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 Laser-Induced Growth of Titanium Nitride Microcolumns on Biased Titanium Targets

2005 ◽  
Vol 20 (1) ◽  
pp. 62-67 ◽  
Author(s):  
E. György ◽  
A. Pérez del Pino ◽  
P. Serra ◽  
J.L. Morenza
Keyword(s):  
Bias Voltage ◽  
Single Pulse ◽  
Laser Pulses ◽  
High Repetition Rate ◽  
Applied Bias ◽  
Applied Bias Voltage ◽  
Surface Microrelief ◽  
High Repetition ◽  
Melting Threshold ◽  
Biased Samples

Titanium targets with a bias voltage ranging from −500 to +500 V were submitted to multipulse high repetition rate Nd:yttrium aluminum garnet (YAG; λ = 1.064 μm, τ ∼ 300 ns, ν = 30 kHz) laser irradiations in nitrogen at intensity values below the single-pulse melting threshold. The morphology of the TiN structures formed under the cumulative action of the laser pulses on the surface of the unbiased and biased targets was investigated by profilometry and scanning electron microscopy. Under these irradiation conditions, a specific columnar surface microrelief developed. The height of the microcolumns reached about 10–15 μm, and their diameter about 1–2 μm. The development of TiN microcolumns was enhanced by the applied bias voltage. The enhancement in the negative biased samples was stronger than that in the positive biased ones.

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.

scholarly journals High-Repetition-Rate Femtosecond Laser Processing of Acrylic Intra-Ocular Lenses

Polymers ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 242 ◽  
Author(s):  
Daniel Sola ◽  
Rafael Cases
Keyword(s):  
Femtosecond Laser ◽  
Repetition Rate ◽  
Laser Processing ◽  
Refractive Index Change ◽  
Laser Pulses ◽  
Processing Parameters ◽  
High Repetition Rate ◽  
Femtosecond Laser Pulses ◽  
Periodic Patterns ◽  
High Repetition

The study of laser processing of acrylic intra-ocular lenses (IOL) by using femtosecond laser pulses delivered at high-repetition rate is presented in this work. An ultra-compact air-cooled femtosecond diode laser (HighQ2-SHG, Spectra-Physics) delivering 250 fs laser pulses at the fixed wavelength of 520 nm with a repetition rate of 63 MHz was used to process the samples. Laser inscription of linear periodic patterns on the surface and inside the acrylic substrates was studied as a function of the processing parameters as well as the optical absorption characteristics of the sample. Scanning Electron Microscopy (SEM) Energy Dispersive X-ray Spectroscopy (EDX), and micro-Raman Spectroscopy were used to evaluate the compositional and microstructural changes induced by the laser radiation in the processed areas. Diffractive characterization was used to assess 1st-order efficiency and the refractive index change.

scholarly journals Interaction of Long Time Pulses of an Nd3+:YAG Laser Beam with the Heusler AlloyNi45Co5Mn35.5In14.5

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7016
Author(s):  
Patryk Ciupak ◽  
Artur Barłowski ◽  
Piotr Sagan ◽  
Tadeusz Jasiński ◽  
Marian Kuzma
Keyword(s):  
Laser Radiation ◽  
Laser Processing ◽  
Damage Threshold ◽  
Laser Pulses ◽  
Bulk Sample ◽  
Laser Interaction ◽  
Yag Laser ◽  
Long Time ◽  
Layer Sample ◽  
Melting Threshold

In this paper, the laser processing of the surface of bulk and layered samples (of thickness 75 nm) of Ni45Co5Mn35.5In14.5 alloy (NC5MI) was investigated using microsecond laser pulses. A Q-switched pulsed Nd3+:YAG laser, operating in the 1st harmonic (which had a wavelength of 1064 nm) with a pulse duration of 250 µs, was used. NC5MI is a metal resistant to thermal laser processing because its reflection coefficient is close to unity for long wavelengths. The aim of this paper was to learn the forms of laser processing (heating, microprocessing, ablation) for which the above-specified type of laser is useful. The samples were irradiated with various fluences in the interval of 5–32 J·cm−2. The effect of the laser interaction with the surface was explored by SEM microscopy. The threshold fluences for the bulk sample were determined as: the visible damage threshold (Fthd = 2 ± 0.2 J·cm−2), the melting threshold (Fthm = 10 ± 0.5 J·cm−2), and the deep melting threshold (Fthdm = 32 J·cm−2). Unexpectedly, these values wereincreased for the layer sample due to its silicon substrate. We have concluded that this type of laser radiation is advantageous for the annealing and melting of, or drilling holes in, the alloy, but disadvantageousto the ablation of the alloy.

scholarly journals Biomimetic surface structures in steel fabricated with femtosecond laser pulses: influence of laser rescanning on morphology and wettability

2018 ◽  
Vol 9 ◽  
pp. 2802-2812 ◽  
Author(s):  
Camilo Florian Baron ◽  
Alexandros Mimidis ◽  
Daniel Puerto ◽  
Evangelos Skoulas ◽  
Emmanuel Stratakis ◽  
...  
Keyword(s):  
Femtosecond Laser ◽  
Repetition Rate ◽  
Laser Processing ◽  
Laser Pulses ◽  
High Repetition Rate ◽  
Femtosecond Laser Pulses ◽  
Surface Structures ◽  
Complex Structures ◽  
Direct Writing ◽  
Wide Range

The replication of complex structures found in nature represents an enormous challenge even for advanced fabrication techniques, such as laser processing. For certain applications, not only the surface topography needs to be mimicked, but often also a specific function of the structure. An alternative approach to laser direct writing of complex structures is the generation of laser-induced periodic surface structures (LIPSS), which is based on directed self-organization of the material and allows fabrication of specific micro- and nanostructures over extended areas. In this work, we exploit this approach to fabricate complex biomimetic structures on the surface of steel 1.7131 formed upon irradiation with high repetition rate femtosecond laser pulses. In particular, the fabricated structures show similarities to the skin of certain reptiles and integument of insects. Different irradiation parameters are investigated to produce the desired structures, including laser repetition rate and laser fluence, paying special attention to the influence of the number of times the same area is rescanned with the laser. The latter parameter is identified to be crucial for controlling the morphology and size of specific structures. As an example for the functionality of the structures, we have chosen the surface wettability and studied its dependence on the laser processing parameters. Contact angle measurements of water drops placed on the surface reveal that a wide range of angles can be accessed by selecting the appropriate irradiation parameters, highlighting also here the prominent role of the number of scans.

Heat input and accumulation for ultrashort pulse processing with high average power

2018 ◽  
Vol 7 (3) ◽  
pp. 145-155 ◽  
Author(s):  
Johannes Finger ◽  
Benedikt Bornschlegel ◽  
Martin Reininghaus ◽  
Andreas Dohrn ◽  
Markus Nießen ◽  
...  
Keyword(s):  
Laser Radiation ◽  
Heat Input ◽  
Ultrashort Pulse ◽  
Average Power ◽  
High Repetition Rate ◽  
Materials Processing ◽  
Heat Accumulation ◽  
Absorbed Energy ◽  
Pulse Processing ◽  
Ultrashort Laser

Abstract Materials processing using ultrashort pulsed laser radiation with pulse durations <10 ps is known to enable very precise processing with negligible thermal load. However, even for the application of picosecond and femtosecond laser radiation, not the full amount of the absorbed energy is converted into ablation products and a distinct fraction of the absorbed energy remains as residual heat in the processed workpiece. For low average power and power densities, this heat is usually not relevant for the processing results and dissipates into the workpiece. In contrast, when higher average powers and repetition rates are applied to increase the throughput and upscale ultrashort pulse processing, this heat input becomes relevant and significantly affects the achieved processing results. In this paper, we outline the relevance of heat input for ultrashort pulse processing, starting with the heat input of a single ultrashort laser pulse. Heat accumulation during ultrashort pulse processing with high repetition rate is discussed as well as heat accumulation for materials processing using pulse bursts. In addition, the relevance of heat accumulation with multiple scanning passes and processing with multiple laser spots is shown.

Modeling of Ultrashort Pulse Laser Ablation in Water

2009 ◽  
Author(s):  
Jian Jiao ◽  
Zhixiong Guo ◽  
Kunal Mitra
Keyword(s):  
Heat Transfer ◽  
Electron Density ◽  
Rate Equation ◽  
Free Electron ◽  
Radiative Heat ◽  
Temporal Evolution ◽  
Optical Breakdown ◽  
Laser Pulses ◽  
Maximum Plasma ◽  
Free Electron Density

A numerical model combining the ultrafast radiative heat transfer and ablation rate equation for free electron density is proposed to investigate the transient process of plasma formation in distilled water. The focused beam propagation governed by the transient equation of radiative heat transfer is solved by the transient discrete ordinates method. The temporal evolution of free electron density governed by the rate equation is solved using a forth-order Runge-Kutta method. Two laser pulses: 30 ps and 300 fs are considered. Simulation of the dynamics of plasma formation is performed. The results include the threshold laser intensity for optical breakdown, temporal evolution and spatial distribution of the free electron density as well as the maximum plasma length. To validate the model, optical breakdown thresholds for different laser pulses, the shape of plasma breakdown region and the maximum plasma length predicted by the present model are also compared with the experimental data.

scholarly journals Ultrafast Third-Order Nonlinear Optical Response Excited by fs Laser Pulses at 1550 nm in GaN Crystals

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3194
Author(s):  
Adrian Petris ◽  
Petronela Gheorghe ◽  
Tudor Braniste ◽  
Ion Tiginyanu
Keyword(s):  
Harmonic Generation ◽  
Nonlinear Optical ◽  
Laser Pulses ◽  
Third Harmonic Generation ◽  
High Repetition Rate ◽  
Third Order ◽  
Third Harmonic ◽  
The Third ◽  
High Repetition ◽  
Gan Crystal

The ultrafast third-order optical nonlinearity of c-plane GaN crystal, excited by ultrashort (fs) high-repetition-rate laser pulses at 1550 nm, wavelength important for optical communications, is investigated for the first time by optical third-harmonic generation in non-phase-matching conditions. As the thermo-optic effect that can arise in the sample by cumulative thermal effects induced by high-repetition-rate laser pulses cannot be responsible for the third-harmonic generation, the ultrafast nonlinear optical effect of solely electronic origin is the only one involved in this process. The third-order nonlinear optical susceptibility of GaN crystal responsible for the third-harmonic generation process, an important indicative parameter for the potential use of this material in ultrafast photonic functionalities, is determined.

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