Simulations of laser-driven targets with thin high-Z coatings
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Abstract The work is devoted to the problem of forming micro- and nanoscale elements topologies of high-resolution by means of controlled treatment of material surface with ultrashort laser pulses. The technology of processing thin-film coatings by the method of selective laser ablation is described. The possibility of using a high-voltage electrostatic field for collecting ablation products and preventing their deposition on the surface of formed microstructures is shown.
Laser Ablation
Deposition
High Voltage
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We have established a methodology to stabilize the laser energy density on a target surface in pulsed laser deposition of thin films. To control the focused laser spot on a target, we have imaged a defined aperture in the beamline (so called image-focus) instead of focusing the beam on a target based on a simple “lens-focus.” To control the laser energy density on a target, we have introduced a continuously variable attenuator between the output of the laser and the imaged aperture to manipulate the energy to a desired level by running the laser in a “constant voltage” mode to eliminate changes in the lasers’ beam dimensions. This methodology leads to much better controllability/reproducibility for reliable pulsed laser deposition of high performance electronic thin films.
Attenuator (electronics)
Pulsed Laser Deposition
Aperture (computer memory)
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Laser-induced breakdown spectroscopy
Nanosecond
Laser Ablation
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An analytical model is derived to describe the stress mechanism in a thin film against the laser-induced damage threshold (LIDT) based on the thermal transfer equation.Different structures of high-reflection films at 355 nm are prepared to validate this model.LIDTs are found to have a linear relationship with stress.Furthermore, predictions from the simple model agree with the experiments.
Nanosecond
Ultraviolet
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Space laser systems are widely used in communication, altimeter and Doppler radar. UV laser, which possesses high spectral resolution and provides with the detection of the parallel polarized molecular (Rayleigh) and particle (Mie) backscattered signals has promising use in atmosphere detection and Doppler radar. No orbiting satellite carrying with 355nm laser has yet been launched owing to the laser induced damage of coatings. Coatings for spaceborne laser system are widely used in spacecraft with laser system to improve the transmittance of the optical system and to adjust the laser beams. An effective way to improve the lifetime of the coatings and the resistance to the environment is to increase laser induced damage threshold (LIDT). The subsurface damage (SSD) of the substrate is one of the major harmful factors in laser induced damage. In our study, 355nm high-reflection (HR) and anti-reflective (AR) coatings deposited by dual-ion beam sputtering (DIBS) were stable and showed lit
Optical coating
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We report a parameteric investigation of the damage threshold and morphology of nine frequently employed dielectric coatings as a function of pulse length (5 and 15 ns), frequency (1.06, 0.53, 0.35, and 0.26 μm), and film thickness. A vidicon camera and computer were used to obtain real-time laser spatial profiles for each testing event. This technique greatly reduced the time required to obtain damage thresholds and enabled a large matrix of data to be obtained. The data and damage morphologies are discussed and several important conclusions are drawn concerning pulsed laser-induced damage to optical materials in thin-film form.
Pulsed Laser Deposition
Optical coating
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Laser Ablation
Pulsed Laser Deposition
Deposition
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Simulations of laser-fused silica interactions at 0.351 μm are a key issue in predicting and quantifying laser damage in large laser systems such as LIL and LMJ. Validation of numerical simulations requires detailed knowledge of the different parameters involved in the interaction. To concentrate on a simple situation, we have made and tested a thin film system based on calibrated gold nanoparticles (0.2-0.8 μm diameter) inserted between two silica layers. The fused silica overcoat was either 2 or 10 microns thick. We have performed simulations of laser energy deposition in the engineered defect (i.e. nanoparticle) and the surrounding fused silica taking into account various laser/defect induced absorption mechanisms of SiO2 (radiative ionization, avalanche and multiphotonic ionization). We have studied crater formation produced by the absorber explosion with a 2D Lagrange-Euler code taking into account crack formation and propagation in the brittle material. We discuss the influence of the defect depth (with respect to the surface) on the damage morphology. The simulations are compared with our experimental results.
Laser Ablation
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Large-aperture deposition of high-laser-damage-threshold, low-dispersion optical coatings for 15 femtosecond pulses have been developed using plasma-ion-assisted electron-beam evaporation. Coatings are demonstrated over 10 in. aperture substrates.
Optical coating
Aperture (computer memory)
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