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Laser-induced thermal emission of rough carbon surfaces
摘要： The decay of thermal emission of rough surface layers of different carbon materials under the pulsed laser excitation is analyzed both theoretically and experimentally. For pulsed laser heating of rough surfaces, computer simulations revealed that laser-induced thermal radiation is mainly emitted by peaks of the surface relief, and the emission decay time depends on the relation between the laser penetration depth and the temperature diffusion length. It is also concluded that the presence of surface roughness can significantly increase the emission decay time. In the experiments, carbon materials with different thermal characteristics were used; however, all of the investigated samples demonstrated close values of the emission decay time. This fact shows that the material’s characteristics on the peaks of surface relief are similar for different carbon materials at high temperature.
关键词： laser-induced thermal emission,rough surfaces,carbon materials
更新于2025-09-16 10:30:52
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Dual-Band Frequency Selective Surface on Aperture-Coupled Patch Resonators with Different Polarization Rotation
摘要： In this letter, a dual-band frequency selective surface (FSS) based on aperture-coupled patch resonators is proposed to achieve different angles of polarization rotation, that is, 90o and 0o. The dual-band response is achieved by periodically arranging two independent sub-elements consisting of back-to-back patch resonators with coupling apertures etched on the middle metallic layer. Herein, the first passband is realized by the crossed patch resonators with a pair of rectangular apertures etched beneath the edges of the crossed patches. It can produce 180o phase difference between the two orthogonal components of a linearly polarized (LP) incident wave oriented to the diagonal of the FSS elements, thus rotating the incident polarization to its orthogonal one in this first passband. The second passband is caused by the square patch resonators with crossed apertures etched beneath the center of the square patches, thereby maintaining the incident polarization unchanged in this second passband. The operation principle is then extensively analyzed and discussed. To validate the design concept, the proposed FSS is designed, fabricated, and measured. Good agreement between the measured and simulated results is achieved to reveal the attractive dual-band and dual-polarization features of the proposed FSS.
关键词： Dual-band,aperture-coupled patch resonators,polarization rotation,frequency selective surfaces
更新于2025-09-16 10:30:52
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Solar Engineering of Thermal Processes, Photovoltaics and Wind || Radiation Characteristics of Opaque Materials
摘要： This chapter begins with a detailed discussion of radiation characteristics of surfaces. For many solar energy calculations only two quantities are required, the solar absorptance and the long-wave or infrared emittance, usually referred to as just absorptance and emittance. Although values of these two quantities are often quoted, other radiation properties may be the only available information on a particular material. Since relationships exist between the various characteristics, it may be possible to calculate a desired quantity from available data. Consequently, it is necessary to understand exactly what is meant by the radiation terms found in the literature, to be familiar with the type of information available, and to know how to manipulate these data to get the desired information. The most common type of data manipulation is illustrated in the examples, and readers may wish to go directly to Section 4.5.
关键词： selective surfaces,solar energy,infrared emittance,solar absorptance,radiation characteristics
更新于2025-09-16 10:30:52
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An Automated Setup for Measuring the Light-Scattering Characteristics of Samples with Rough Surfaces at Laser Wavelengths in the Range of 0.35–1.1 μm
摘要： The description and the operating algorithm of an automated scanning device, which is constructed according to the scheme of a two-coordinate goniophotometer and is intended for measuring the bidirectional reflection function (BDRF) of samples with different degrees of surface roughness at laser wavelengths of 0.53, 0.63, and 1.06 μm, are described. The relative measurement error of the BDRF is 6–9%. Special software and the design features allow one to vary the time and scanning step of the device, while the presence of two measurement channels makes it possible to use radiation sources with a nonstabilized output power. The device has the ability to displace the operating spectral range to the region of the middle and far IR range.
关键词： rough surfaces,BDRF,automated setup,bidirectional reflection function,laser wavelengths,light-scattering characteristics
更新于2025-09-12 10:27:22
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Self-assembly of coordination polymers on plasmonic surfaces for computer vision decodable, unclonable and colorful security labels
摘要： Incorporating security labels with physical unclonable functions (PUFs) into products is considered as the most effective anti-counterfeiting measure. Here we reported a PUF-based security label composed of random colorful patterns. The security label was fabricated through self-assembly of coordination polymers – a cupric bromide complex of pyrazine 1,4-dioxide – on lithographically defined plasmonic surfaces. The coordination polymer exhibits excitation wavelength dependent fluorescence fingerprints, which enables encoding spectral information in the polymer. The fluorescence peaks of each spectrum can be easily converted to a unique anti-counterfeiting barcode. The developed security label also carries 2D graphical information, which can be visualized under bright-field, dark-field and fluorescence multifunctional microscopy. It is multi-colored with high contrast under the bright/dark-field modes and single color under fluorescence mode. The multicolors originate from polymer-thickness dependent optical interference. The encryption with colors on a 50 lm square produces a minimum of 3739 PUF codes for the realized authentication system. Moreover, we developed a convenient and reliable authentication strategy based on the computer vision technique to verify the colorful PUF patterns with different definition, rotation angles, brightness, magnification and a mixture of these factors. A high correct validation rate of 100% is achieved using a match threshold of 0.3.
关键词： anti-counterfeiting,coordination polymers,plasmonic surfaces,security labels,physical unclonable functions,computer vision
更新于2025-09-12 10:27:22
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Reconfigurable Surfaces Based on Photocontrolled Dynamic Bonds
摘要： Photocontrolled surfaces have attracted increasing interest because of their potential applications in lithography, photopatterning, biointerfaces, and microfluidics. Light provides high spatiotemporal resolution to control functions of such surfaces without getting into direct contact. However, conventional photocontrolled surfaces can only be switched between two states (on and off). The development of photocontrolled reconfigurable surfaces that can be switched among multiple states is highly desirable because these surfaces can adapt to rapid environmental changes or different applications. Herein, recent developments of photocontrolled reconfigurable surfaces are reviewed. Specially, reconfigurable surfaces based on photocontrolled reversible reactions including thiol-quinone methide, disulfide exchange, thiol-disulfide interconversion, diselenide exchange, and photosubstitution of Ru complexes are highlighted. As a perspective, other photocontrolled dynamic bonds that can be used to construct reconfigurable surfaces are summarized. Remaining challenges in this field are discussed.
关键词： reconfigurable surfaces,photoswitches,photochemistry,dynamic bonds,photoresponsive
更新于2025-09-12 10:27:22
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Design and Fabrication of Dual-Scale Broadband Antireflective Structures on Metal Surfaces by Using Nanosecond and Femtosecond Lasers
摘要： Antire?ective surfaces, with their great potential applications, have attracted tremendous attention and have been the subject of extensive research in recent years. However, due to the signi?cant optical impedance mismatch between a metal surface and free space, it is still a challenging issue to realize ultralow re?ectance on a metal surface. To address this issue, we propose a two-step strategy for constructing antire?ective structures on a Ti-6Al-4V (TC4) surface using nanosecond and femtosecond pulsed lasers in combination. By controlling the parameters of the nanosecond laser, microgrooves are ?rst scratched on the TC4 surface to reduce the interface re?ection. Then, the femtosecond laser is focused onto the sample surface with orthogonal scanning to induce deep air holes and nanoscale structures, which e?ectively enhances the broadband absorption. The antire?ection mechanism of the dual-scale structures is discussed regarding morphological characterization and hemispherical re?ectance measurements. Finally, the modi?ed sample surface covered with micro-nano hybrid structures is characterized by an average re?ectance of 3.1% over the wavelengths ranging from 250 nm to 2250 nm.
关键词： nanosecond laser,broadband spectrum,femtosecond laser,micro-nano hybrid structures,antire?ective surfaces
更新于2025-09-12 10:27:22
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Experimental study of droplet shedding on laser-patterned substrates
摘要： An experimental study was performed to investigate the dynamics of droplet shedding under the effect of various shear flow speeds on a laser micromachined surface with superhydrophobic properties. To account for the effect of liquid properties on droplet shedding, four different liquids were used in these sets of experiments, namely, distilled water, ethylene glycol, propylene glycol, and glycerol. The wetting length of the liquid droplets was measured based on the air shear speed, and three different regimes were observed based on the critical Weber and Ohnesorge numbers. In the first regime, where the Weber and Ohnesorge numbers are low, droplets deform with slight movement or rotation without detachment from the surface. Under the second regime, where the Weber number is relatively high and the Ohnesorge number is low, droplets deform and detach from the surface, and then subsequent breakup may occur. The variation of droplet detachment time with the Weber and Ohnesorge numbers is further discussed in this paper. In the third regime, where the Ohnesorge number is high, there is no droplet detachment nor are rivulets formed. Finally, empirical correlations are developed to predict the droplet behavior on laser-patterned surfaces under the effect of shear flow. This work can be used as a baseline to study the droplet dynamics on a superhydrophobic surface in cases where temperature changes the liquid properties.
关键词： superhydrophobic surfaces,Ohnesorge number,droplet shedding,laser micromachining,Weber number
更新于2025-09-12 10:27:22
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Combined effects of nanosecond laser-induced surface oxidation and nanostructure formation for selective colorization of nickel surfaces
摘要： Metal surfaces can be nanostructured by laser irradiation making use of different effects ranging from thin film generation to nanostructures formation. Here, the colorization of pure nickel surfaces by nanosecond laser irradiation in air is demonstrated and studied in detail. Correlations between chromaticity coordinates and laser-processing parameter show that the accumulated fluence is the dominating factor in creation of a specific colored surface. The color of the laser-irradiated surfaces shows both angle-dependent and angle-independent in reliance on the processing conditions. The examination of the laser-colored surface demonstrates that lateral and vertical organized, laser-induced structures with nano-, micro-, and mesoscopic scales can be found simultaneously which contribute to the colorization in a particular manner. A comprehensive analysis of the processes involved in the color formation at nickel was performed by examining the surfaces by SEM, reflectometry, XPS, and XRD to verify the multi-process mechanisms of color formation. The most saturated colors result from interference effects within the redeposited layers. It was found that controlling the hatching distance applying optimized laser fluence enables a wider color range and allows a very precise setting of the color. Based on the extracted laser-processing parameters, the surface coloration of arbitrary pattern with desired optical properties becomes practicable, and nanosecond laser color marking can, therefore, be expanded to potentially new applications.
关键词： colorization,nanosecond laser,nickel surfaces,surface oxidation,nanostructure formation
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Laser Engineered Surface Structures for Custom Design of Secondary Electron Yield
摘要： Secondary Electron Yield (SEY) occurs in a system when a primary electron impinges a material’s surface and induces the emission of a 1st and potentially 2nd generation secondary electrons. The total number of secondary electrons per primary electron is the SEY. This phenomenon forms a highly challenging problem in many systems, for example in particle accelerators, where significant levels of SEY form as an electron cloud and can perturbate the circulating beams and generate a high level of heat load to be absorbed by cooling and cryogenics. The Large Hadron Collider (LHC) has a 54-km beam pipe in which copper-laminated steel beam-screens are placed in order to shield the beam pipes from heat loads, but inherently result in unwanted SEY. As such, the development of methods which mitigate the SEY are increasingly appealing, including surface texturing, shaping the geometry and orientation of patterns etched into the surfaces, and carbon-coating of the interior of the beam pipes in the Super Proton Synchrotron (SPS). Previously we have shown that nanosecond pulsed laser treatment of copper surfaces at 532 nm could significantly increase the optical absorbance of the surface, and furthermore reduce the SEY to close to 1. More recently we demonstrated that surface structures produced by a picosecond pulsed laser at 532nm exhibited SEY values below 1 and were successfully tested in a dipole magnet in the Super Proton Synchrotron (SPS) accelerator at CERN.
关键词： laser treatment,Secondary Electron Yield,copper surfaces,SEY,particle accelerators
更新于2025-09-11 14:15:04