Influence of the Characteristics of Multilayer Interference Antireflection Coatings Based on Nb, Si, and Al Oxides on the Laser-Induced Damage Threshold of ZnGeP2 Single Crystal

In this work, the effect of the defect structure and the parameters of antireflection interference coatings based on alternating layers of Nb2O5/Al2O3 and Nb2O5/SiO2 layers on the laser-induced damage threshold of ZGP crystals under the action of Ho:YAG laser radiation at a wavelength of 2.097 μm was determined. Coating deposition was carried out using the ion-beam sputtering method. The laser-induced damage threshold of the sample with a coating based on alternating layers Nb2O5 and SiO2 was W0d = 1.8 J/cm2. The laser-induced damage threshold of the coated sample based on alternating layers of Nb2O5 and Al2O3 was W0d = 2.35 J/cm2. It has been found that the presence of silicon conglomerates in an interference antireflection coating leads to a decrease in the laser-induced damage threshold of a nonlinear crystal due to local mechanical stresses and the scattering of incident laser radiation.

Nature of Photoelectric Effect in a Ge-on-Si SPAD at Ultralow Energy in Incident Pulsed Laser Radiation

The photoelectric effect in a Ge-on-Si single-photon avalanche detector (SPAD) at an ultralow energy in incident pulsed laser radiation is considered in the frame of the classical theory of the electrodynamics of continuous media. It is shown that the energy of incident laser radiation which is shared among a huge number of electrons in a Ge matrix can concentrate on only one of these through the effect of the constructive interference of the fields re-emitted by surrounding electrons. Conservation of energy in this case is upheld because of a substantial narrowing of the effective bandgap in heavily doped p-Ge, which is used in the design of the SPAD considered.

Eliminating Laser Induced Elemental U-Pb Fractionation using low sample volume multi-shot ablation protocols

<p>The interaction of incident laser radiation and sample substrate is complex and difficult to predict. Natural zircons areoften both structurally and chemically heterogeneous in 3-dimensional space. Encountering growth-related, structural micro-heterogeneities, inclusions and chemical complexities is almost inevitable when employing ‘conventional’ static, high-frequency laser sampling protocols often lasting several tens of seconds at a time.</p><p> </p><p>A multi-shot approach to laser ablation by contrast implements a minimal sample exposure time to incident laser radiation by applying multiple 1 Hz shots in delayed succession to a single sampling site. This process can be conceptualised as a “slowing down” of a high-frequency (10-20 Hz) static Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) analysis. Each laser pulse applied in this manner, produces signal peak which is distinct albeit transient. The ability to integrate and collate signal pulses for a small number of consecutive laser shots (10-30 shots), as opposed to continuously pulsing the laser, produces highly precise age determinations (<1% reproducibility, 2slevel) on small sample volumes (~695µm<sup>3 </sup>on 91500 zircon standard). The multi-shot LA-ICP-MS protocol employed here effectively eliminates ‘downhole’ fractionation as the resultant craters are extremely shallow (as shallow as ~553nm on 91500 zircon standard) and maintain an aspect ratio of <<1. Further benefits include a reduced probability of thermally induced effects (e.g., substrate melting), plasma loading, and the potential for signal mixing (with depth) in a heterogeneous sample.</p>

Высокоэффективное преобразование лазерного излучения высокой плотности

AlGaAs/GaAs-based semiconductor photovoltaic converters (PVCs) of laser radiation, capable of operating at an illuminance up to 9 kW/cm^2 with retained isothermal state have been studied. This state was confirmed by the logarithmic shape of dependences of the open-circuit voltage on the power density of incident laser radiation. At maximum illuminance, the open-circuit voltage level was close to 1.33 V. It is shown that the proposed PVCs can provide laser radiation conversion at an 840-nm wavelength with efficiency above 51% at an incident radiation power density of 2.5 kW/cm^2.

Investigation of absorption of laser radiation by copperand nickel-based powders to obtain gradient materials by selective laser melting

The absorption of laser radiation of powder materials based on copper and nickel is studied. The dependence of the temperature of the powder material on the power of the incident laser radiation is obtained. A comparison of the values obtained by different measurement methods is presented.

Thermal transport across a thin film composite due to laser short-pulse heating

Laser short-pule irradiation of silicon-diamond-aluminum thin films is considered and energy transport across the films is modelled using the Boltzmann transport equation. Electron-phonon coupling is adopted to formulate energy transfer across the electron and lattice sub-systems in the aluminum film. Thermal boundary resistance is incorporated at the film interfaces. The transfer matrix method is used to account for the transmittance, reflection and absorption of the incident laser radiation across the films. Equivalent equilibrium temperature is introduced to access energy transport in the films, which represents the average energy of all phonons around a local point when they redistribute adiabatically to an equilibrium state. It is found that equivalent equilibrium temperature increases sharply in the electron sub-system due to electron excess energy gain from the irradiated field. Equivalent equilibrium temperature decays gradually in the lattice sub-system with increasing period due to phonon scattering in the film.

Numerical Simulation of Thermal Stress Fields in Thermoplastics in a Pulsed Laser Welding Process

A numerical simulation code is developed and used to derive relationships between the incident laser radiation, the thermal stress field, and the size and shape of the heat affected (HAZ) and melt zones for a pulsed laser transmission welding process. The material used in the investigation is a high density polyethylene thermal plastic. The numerical model uses the Fourier heat conduction thermal model and the welding process involves the lap welding of two thin layers of thermoplastic films with the welding conditions of a transparent material over a semi-transparent or opaque material. The Fourier model is valid due to the high thermal pulse velocity through the material. The results are compared to the published data on thermoplastic welding criteria and the legitimacy of these criteria are discussed.

Microgravity Processing of Biopolymer/Metal Composites for NLO Applications

The overall objective of this project is the development of NLO-active materials with optical clarity and mechanical strength. These materials are intended for laser eye protection. By combining χ2 and χ3 optical properties, the intensity of incident laser radiation may be efficiently reduced. Using an in-plane poling technique, aligned films of liquid crystal poly(benzyl-Lglutamate), PBLG, were made which showed higher second harmonic generation (SHG) values compared to quartz. Silver sols in the 10-90 nm diameter size range were complexed with tricyanovinyl aniline, TCVA, resulting in composite PBLG/Ag Sol films with higher than at least an order of magnitude of χ3 values materials such as polydiacetylenes and nitroanilines. These polymeric NLO materials offer definite advantages in terms of easy processability into films for the manufacture of the optical elements necessary for laser eye protection.

Compact Laser Source for Metal Deposition

For the past few years, there has been considerable interest in using lasers for the directed deposition of metal [1,2,3,4]. Part of this interest is driven by technological applications in microelectronics. In particular, this includes the rapid interconnection of gate arrays [5] and the repair of defects in photomasks [6]. The techniques used for the laser patterning of metal include Laser Chemical Vapor Deposition (LCVD) [7], and the decomposition of spin-coated organometallic inks [8]. In the first process, LCVD, a laser with a power of several hundred milliwatts or more is used to irradiate a substrate in the presence of an organometallic vapor. The substrate is chosen so that it absorbs the the incident laser radiation while, in general, the organometallic vapor is transparent at the laser wavelength. The absorption of the laser energy by the substrate results in a temperature rise which depends on the thermal properties of the substrate. If the temperature rise is sufficient, organometallic molecules impinging on the irradiated area decompose. Non-volatile components (such as metal fragments) remain on the surface and form a deposit. In the second process, decomposition of organometallic films, a substrate which was previously spin coated with an organometallic ink is irradiated wherever metal patterns are desired. The ink decomposes in these areas leaving a film of metal. The unirradiated areas of the ink are then washed away with a suitable solvent. Such processes have been extensively studied and developed using primarily argon, krypton, and CO2 lasers [1,2,3,4]. In general these lasers are large, expensive, require maintenance, and raise reliability concerns. These characteristics add to the challenge of introducing laser deposition processes into the manufacturing environment.

Neutral and Ionic Particle Emission Produced by Laser Irradiation of a GaAs Surface

The emission of gas phase particles from a GaAs surface, due to irradiation at 1064 nm by an unfocussed Q-switched Nd:YAG laser beam, has been studied. Mass spectra have been recorded with the aid of a quadrupole mass spectrometer, and the ion-neutral ratio of the emitted particles has been measured with an electrical diode set up. The applied incident laser radiation power density was varied in the range 1.2–9.6 × 107 Watts/cm2 and was delivered as 10 ns (fwhm) long pulses. It appeared that mainly Ga atoms and As2 molecules were emitted, together with minor amounts (<1%) of Ga2 and GaAs molecules. Besides the emission of neutral particles, the formation of Ga+ atomic ions was observed. By measuring the ratio of Ga+ ions and Ga neutral atoms it could be shown that the (ionic) particle emission is governed by a thermal mechanism for 1064 nm incident radiation. This latter experimental result differs from that obtained if a ruby laser (694 nm) is used as the radiation source.