Photomechanical Processes and Effects in Ablation

Paltauf, Guenther; Dyer, P. E.

doi:10.1021/cr010436c

Cited by 344 publications

(205 citation statements)

References 127 publications

(364 reference statements)

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“…The maximum values of the laser-induced stresses and the contribution of the so-called photomechanical effects to the material modification and damage are related to the condition of stress confinement [5,78,82,[157][158][159][160]. In systems with relatively slow heat conduction and fast thermalization of the deposited laser energy, the condition for the stress confinement is mainly defined by the laser penetration depth, L p , and the laser pulse duration, τ p .…”

Section: Photomechanical Spallationmentioning

confidence: 99%

Atomic/Molecular-Level Simulations of Laser–Materials Interactions

Zhigilei

Lin

Ivanov

et al. 2009

Laser-Surface Interactions for New Materials Production

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Summary. Molecular/atomic-level computer modeling of laser-materials interactions is playing an increasingly important role in the investigation of complex and highly nonequilibrium processes involved in short-pulse laser processing and surface modification. This chapter provides an overview of recent progress in the development of computational methods for simulation of laser interactions with organic materials and metals. The capabilities, advantages, and limitations of the molecular dynamics simulation technique are discussed and illustrated by representative examples. The results obtained in the investigations of the laser-induced generation and accumulation of crystal defects, mechanisms of laser melting, photomechanical effects and spallation, as well as phase explosion and massive material removal from the target (ablation) are outlined and related to the irradiation conditions and properties of the target material. The implications of the computational predictions for practical applications, as well as for the theoretical description of the laser-induced processes are discussed. IntroductionShort-pulse lasers are used in a diverse range of applications, from advanced materials processing, cutting, drilling, and surface micro-and nanostructuring [1,2] to pulsed-laser deposition of thin films and coatings [3], laser surgery [4,5], and artwork restoration [6,7], and to the exploration of the conditions for inertial confinement fusion, with the world's most energetic laser system being built at the National Ignition Facility at Lawrence Livermore National Laboratory [8]. At the fundamental science level, short-pulse laser irradiation has the ability to bring material into a highly nonequilibrium state and provides a unique opportunity to probe the material behavior under extreme conditions. In particular, optical pump-probe experiments have been used to investigate transient changes in the electronic structure of the irradiated surface with high (often subpicosecond) temporal resolution [9][10][11][12][13], whereas recent advances in time-resolved X-ray and electron diffraction

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Section: Photomechanical Spallationmentioning

confidence: 99%

Atomic/Molecular-Level Simulations of Laser–Materials Interactions

Zhigilei

Lin

Ivanov

et al. 2009

Laser-Surface Interactions for New Materials Production

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“…No shifts in the positions of the diffraction peaks and no splitting of the peaks have been observed in this study as well as in time-resolved x-ray diffraction investigations of even faster nonthermal melting processes. 5,6 The absence of the shifts and splittings of the diffraction peaks can be related to the condition of the inertial stress confinement, 22,56 when the lattice heating and melting are taking place as constantvolume processes. In the case of the thermal melting, the time of the lattice heating is defined by the laser pulse duration p , and the time of the electron-phonon equilibration, e-ph , whichever is larger.…”

Section: Conclusion and Connections To Experimentsmentioning

confidence: 99%

Time-resolved diffraction profiles and atomic dynamics in short-pulse laser-induced structural transformations: Molecular dynamics study

2006

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The diffraction profiles and density correlation functions are calculated for transient atomic configurations generated in molecular dynamics simulations of a 20 nm Au film irradiated with 200 fs laser pulses of different intensity. The results of the calculations provide an opportunity to directly relate the detailed information on the atomic-level structural rearrangements available from the simulations to the diffraction spectra measured in time-resolved x-ray and electron diffraction experiments. Three processes are found to be responsible for the evolution of the diffraction profiles. During the first several picoseconds after the laser excitation, the decrease of the intensity of the diffraction peaks is largely due to the increasing amplitude of thermal atomic vibrations and can be well described by the Debye-Waller factor. The effect of thermoelastic deformation of the film prior to melting is reflected in shifts and splittings of the diffraction peaks, providing an opportunity for experimental probing of the ultrafast deformations. Finally, the onset of the melting process results in complete disappearance of the crystalline diffraction peaks. The homogeneous nucleation of a large number of liquid regions throughout the film is found to be more effective in reducing long-range correlations in atomic positions and diminishing the diffraction peaks as compared to the heterogeneous melting by melting front propagation. For the same fraction of atoms retaining the local crystalline environment, the diffraction peaks are more pronounced in heterogeneous melting. A detailed analysis of the real space correlations in atomic positions is also performed and the atomic-level picture behind the experimentally observed fast disappearance of the correlation peak corresponding to the second nearest neighbors in the fcc lattice during the laser heating and melting processes is revealed.

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“…A thorough understanding of the physics and mechanisms of corneal ablation and the potential role of laser repetition rate remains a topic of research [3][4][5][6][7][8][9]. As the exact mechanisms of photoablation remain unidentified, it is critical to show that increasing the laser repetition rate does not reveal any differences in surgical outcome or underlying corneal pathology.…”

Section: Introductionmentioning

confidence: 99%