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Off-Resonance Control and All-Optical Switching: Expanded Dimensions in Nonlinear Optics
摘要： The theory of non-resonant optical processes with intrinsic optical nonlinearity, such as harmonic generation, has been widely understood since the advent of the laser. In general, such effects involve multiphoton interactions that change the population of each input optical mode or modes. However, nonlinear effects can also arise through the input of an off-resonant laser beam that itself emerges unchanged. Many such effects have been largely overlooked. Using a quantum electrodynamical framework, this review provides detail on such optically nonlinear mechanisms that allow for a controlled increase or decrease in the intensity of linear absorption and fluorescence and in the efficiency of resonance energy transfer. The rate modifications responsible for these effects were achieved by the simultaneous application of an off-resonant beam with a moderate intensity, acting in a sense as an optical catalyst, conferring a new dimension of optical nonlinearity upon photoactive materials. It is shown that, in certain configurations, these mechanisms provide the basis for all-optical switching, i.e., the control of light-by-light, including an optical transistor scheme. The conclusion outlines other recently proposed all-optical switching systems.
关键词： absorption,nonlinear optics,all-optical switch,resonance energy transfer,fluorescence,FRET,optical transistor,multiphoton process,laser action,second harmonic generation
更新于2025-09-23 15:19:57
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Near-Surface Plasma Formed by Dual-Pulse Laser Action at Two Wavelengths on Titanium in Air
摘要： Spectra and structures of near-surface plasma torches were studied experimentally by measuring the speci? c mass loss and plume luminosity caused by dual-pulse laser radiation at wavelengths 1064 and 532 nm on titanium in air as functions of the time between laser pulses and their sequence. Dependences of the laser-plasma temperature and concentration of charged particles on the paired laser pulse parameters were established at laser radiation power densities q1064 ≤ 3.1·109 and q532 ≤ 2.7·109 W/cm2 for λ = 1064 and 532 nm. The optimal conditions for recording erosion plasma spectra had the initial effect from second-harmonic radiation with a time interval between pulses of 4–5 μs; for speci? c mass loss, 3–6 μs. The results were important for enhancing the ef? ciency of laser emission spectral analysis and laser-plasma processing of materials.
关键词： speci? c mass loss,laser plasma,plasma-torch structure,plasma temperature,electron concentration,dual-pulse laser action
更新于2025-09-16 10:30:52
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Laser Ablation - From Fundamentals to Applications || Nanosecond Laser Ablation: Mathematical Models, Computational Algorithms, Modeling
摘要： The basic mathematical models, computational algorithms, and results of mathematical modeling of various modes of laser action on metals are considered. It is shown that for mathematical description and analysis of the processes of laser heating, melting, and evaporation of condensed media, various theoretical approaches are used: continuum, kinetic, atomistic, etc. Each of them has its own field of applicability, its advantages, and disadvantages. Mathematical description of ns-laser ablation is usually carried out within the framework of continuum approach in the form of hydrodynamic models that take into account reaction of irradiated material to varying density, pressure, and energy both in the target and in the vapor-gas medium. Within the framework of continuum approach, a multiphase, multifront hydrodynamic model and computational algorithm were constructed that were designed for modeling ns-PLA of metal targets embedded in gaseous media. It is shown that proposed model and computational algorithm allow to carry out the simulation of interrelated mechanisms of heterogeneous and homogeneous evaporation of metals manifested as a series of explosive boiling. Modeling has shown that explosive boiling in metals occurs due to the presence of a near-surface temperature maximum. It has been established that in ns-PLA, exposure regimes can be realized in which a phase explosion is the main mechanism of material removal. The verification of reliability of obtained results was carried out by comparing experimental data and calculations with atomistic models.
关键词： explosive boiling,phase explosion,hydrodynamic model,laser action,nanosecond pulse,mathematical modeling,subsurface temperature maximum
更新于2025-09-12 10:27:22
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Creation of heterogeneous metal-ceramic structures based on Ti, Ni and WC, B4C by the combined method of laser cladding and cold gas-dynamic spraying
摘要： The paper pioneers the complex experimental investigation of the metal-ceramic coating made by the additive technologies, the combination of the cold gas-dynamic spraying (CS) and following layered laser processing. The coating is made of ceramic powders WC and В4С, the concentration in the initial mixture of 10-70 wt.%, and metal powders based on Ti+Al, the ratio 94:6 wt.%, and Ni. The result is the strategy of the production of the heterogeneous material without pores and cracks by the consequent deposition of the powder by the CS method followed by the laser action; the thickness of the coating is 4 mm.
关键词： laser action,microstructure,morphology,coating,microhardness,cold spraying
更新于2025-09-12 10:27:22
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Formation of Antifriction Alloys on the Metal Materials Surface by Laser Radiation
摘要： In this paper, we present the results of an investigation of the production of antifriction coating based on tin bronze using continuous laser radiation. The powder material was uniformly distributed on a copper substrate and subjected to laser melting under various experimental conditions. X-ray diffraction analysis of the obtained samples was carried out, topology, morphology and tribology of the surface were studied.
关键词： powder,laser action,morphology,bronze coating,melting
更新于2025-09-12 10:27:22