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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) - Analysis of Various Approaches for the Fabrication of Diffractive Optical Elements
摘要： Diffractive Optical Elements (DOEs) exist for a large range of applications. Usually DOEs are obtained by combining lithographic techniques and etching in order to achieve pre-determined phase patterns. That way, it is possible to shape or split laser beams with very high efficiencies. Indeed for binary element which consist of two phase levels (0 and π) the diffraction efficiency is around 75% and this efficiency can approach 100% for multilevel elements. Various illustrations of DOEs can be found in the literature for example using organic materials like photoresists or inorganic materials such as silica or chalcogenide layers. Recent work has shown that DOEs can also be recorded in the volume of photosensitive chalcogenide layers, but no precise comparison of this class of DOEs has ever been made with classical DOEs. In this paper we propose to study binary DOEs fabricated with conventional lithography (based on local control of the thickness) and similar one fabricated using photo-induced refractive index change in As2S3 layers.
关键词： etching,phase patterns,silica,laser beams,photo-induced refractive index change,photoresists,lithography,As2S3 layers,chalcogenide layers,Diffractive Optical Elements,diffraction efficiency
更新于2025-09-16 10:30:52
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Evaluation of Residual Stresses in Laser Welded High-Pressure Vessels Steels by X-Ray Diffraction
摘要： This paper contains results of a comprehensive experimental programme aimed at an evaluation of residuals stresses in and near laser welds of pressure vessels steels using X-ray diffraction method. Welds were prepared by the company RAPTECH s.r.o., where two types of steel plates, namely P355 and P460 of the thickness 5, 8 and 10 mm, were welded by a laser beam with specific parameters. Surface transversal and longitudinal stresses were analysed on both sides of the welds, namely upper and downside. The results, important for further applications of the used technology, are discussed particularly from the viewpoint of possible critical areas near the welds and their impact on fatigue loading.
关键词： X-ray diffraction,laser welds,pressure vessel steels
更新于2025-09-16 10:30:52
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Development of a Monitoring Strategy for Laser-Textured Metallic Surfaces Using a Diffractive Approach
摘要： The current status of research around the world concurs on the powerful influence of micro- and nano-textured surfaces in terms of surface functionalization. In order to characterize the manufactured topographical morphology with regard to the surface quality or homogeneity, major efforts are still required. In this work, an optical approach for the indirect evaluation of the quality and morphology of surface structures manufactured with Direct Laser Interference Patterning (DLIP) is presented. For testing the designed optical configuration, line-like surface patterns are fabricated at a 1064 nm wavelength on stainless steel with a repetitive distance of 4.9 μm, utilizing a two-beam DLIP configuration. Depending on the pulse to pulse overlap and hatch distance, different single and complex pattern geometries are produced, presenting non-homogenous and homogenous surface patterns. The developed optical system permitted the successfully classification of different pattern geometries, in particular, those showing single-scale morphology (high homogeneity). Additionally, the fabricated structures were measured using confocal microscopy method, and the obtained topographies were correlated with the recorded optical images.
关键词： homogeneity characterization,periodic structures,diffraction analysis,direct laser interference patterning,indirect surface characterization
更新于2025-09-16 10:30:52
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Acousto-optic modulators for a controlled frequency shift of light beams in optical and microwave cold-atom frequency standards
摘要： A series of specialised acousto-optic modulators/frequency shifters based on paratellurite (TeO2) single crystals is developed for systems of laser cooling and frequency stabilisation of laser sources in optical and microwave frequency standards based on cold strontium, rubidium and caesium atoms. The methods of calculation and optimisation of the main parameters of acousto-optic modulators are considered; their basic technical characteristics are experimentally investigated in the spectral range of optical radiation 460 – 900 nm and in the frequency shift range of 5 – 400 MHz. The modulators have a high diffraction efficiency, low power consumption and the ability to work with linearly and randomly polarised optical radiation.
关键词： frequency shifter,modulator,acousto-optic diffraction,frequency stabilisation,laser cooling,frequency shift,frequency standards
更新于2025-09-16 10:30:52
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Formation of light with controlled rotation of the polarisation plane by superposing linearly polarised waves
摘要： A method is proposed for generating linearly polarised light, whose polarisation plane rotates at a given frequency. The method is based on the double passage of the light through an acousto-optic modulator made of an anisotropic crystal. An experimental prototype based on a paratellurite crystal is fabricated, with the help of which rotation of linearly polarised light of a He – Ne laser (l = 0.63 mm) is obtained with the frequency controlled by the frequency of sound.
关键词： acousto-optic diffraction,Bragg regime,rotation of the polarisation plane
更新于2025-09-16 10:30:52
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High Energy and Short Pulse Lasers || Phase Manipulation of Ultrashort Soft X-Ray Pulses by Reflective Gratings
摘要： In this chapter, we discuss the use of reflective diffraction gratings to manipulate the phase of ultrashort pulses in the extreme ultraviolet (XUV) and soft X-ray spectral regions. Gratings may be used to condition the spectral phase of ultrashort pulses, e.g., to compensate for the pulse chirp and compress the pulse, similarly to what is routinely realized for visible and infrared pulses. The chirped pulse amplification technique has been already proposed for soft X-ray free-electron laser radiation; however, it requires the use of a compressor to compensate for the pulse chirp and get closer to the Fourier limit. There are fundamental differences when operating the gratings at wavelengths shorter than ≈40 nm on a broad band: (a) the gratings are operated at grazing incidence; therefore, the optical design has to be consequently tailored to this peculiar geometry; (b) the grating efficiency is definitely lower; therefore, the number of diffractions has to be limited to two. We discuss the different configurations that can be applied to the realization of a grating stretcher/compressor.
关键词： extreme ultraviolet,soft X-ray optics,ultrafast optics,diffraction gratings,chirped pulse amplification
更新于2025-09-16 10:30:52
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[IEEE 2019 Thirteenth International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Rome, Italy (2019.9.16-2019.9.21)] 2019 Thirteenth International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Polarizing Beamsplitter Grating based on Asymmetric Slot Waveguide Scatterer
摘要： We demonstrate a novel design for grating-based polarizing beamsplitters (PBSs). The structure has a subwavelength thickness and is engineered to suppress all diffraction orders except for those of the desired orthogonal polarizations. This is achieved by using an asymmetric slot waveguide scatterer unit cell to ensure polarization-selective directional scattering. We ?rst present the design rationale and demonstrate a PBS operating at ～ λ = 752nm that reaches an ef?ciency of ～ 80% for both polarizations with a separation angle of ～ 80? between the polarized light beams. The structure has several advantages over typical grating or metasurface-based implementations, such as high ef?ciency at large separation angles, operation in any re?ection-transmission mode (re?ection only, transmission only, or both) and single periodic element requirement.
关键词： asymmetric slot waveguide,diffraction orders,polarization-selective directional scattering,Polarizing beamsplitters
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - CO <sub/>2</sub> -laser written helical long-period gratings with resonance at second-order diffraction
摘要： We demonstrate the fabrication of helical long-period gratings (HLPGs) with resonance at second-order diffraction for the first time. The torsion, temperature and bending sensing characteristics are investigated experimentally.
关键词： helical long-period gratings,fiber sensing,second-order diffraction
更新于2025-09-16 10:30:52
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Laser Diffraction Evaluation for Soil Particle Size Determination
摘要： Soil particle size distribution is a fundamental soil characteristic that highly affects soil water retention and soil fertility and microbial activity and requires accurate determination. The laser diffraction method is increasingly being applied to measure soil particle size because of its rapid processing, high reproducibility, and detailed analysis for a wide range of size fractions; yet some ambiguities exist regarding the comparability of its results with those obtained by other classical methods. In an article recently published in Soil Science Society of America Journal, researchers evaluate the laser diffraction method by comparing its particle size measurements on hundreds of soil samples collected from a typical cropland in the Beijing mountainous area with those determined by the standard sieve-pipette method and the absolute method of scanning electron microscopy. The team found that laser diffractometry significantly overestimated sand and silt but underestimated clay contents relative to the sieve-pipette method, resulting in soil textural class shifts in nearly half of the soil samples. However, significant linear regression models allow conversion of sand and silt contents between these two methods. In contrast to scanning electron microscopy, the laser diffraction method acquired dissimilar particle size distributions but statistically similar median particle sizes within the clay fraction. Results of this study demonstrate that the laser diffraction method is an effective tool for soil particle size analysis. Future work is needed to examine the applicability of this method in other regions with different soil types and clay mineralogy.
关键词： scanning electron microscopy,sieve-pipette method,soil particle size,laser diffraction
更新于2025-09-16 10:30:52
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Direct observation of elastic softening immediately after femtosecond-laser excitation in a phase-change material
摘要： The generation and propagation of photoexcited elastic waves in crystalline Ge2Sb2Te5 were analyzed by picosecond time-resolved x-ray diffraction using a femtosecond-laser pump and an x-ray free-electron laser probe technique. The crystalline lattice anisotropically expanded initially in approximately 20 ps after the excitation. This was followed by a periodic oscillation of the lattice strain. The elastic stiffness along the cubic [111] direction had significantly softened during the initial expansion, and the strain magnitude was the largest in the [100] and [110] directions. This indicates that femtosecond-laser excitation creates a shallower interlayer potential between the Te and Ge-Sb layers and eventually leads to softening of the elastic stiffness along the cubic [111] direction. Furthermore, this softened state increases the system’s sensitivity to an external stress field. This residual internal stress in a thin film enhances the selective formation of a particular type of variant during the symmetry change from cubic to rhombohedra. This causes the subsequent anisotropic expansion. These phenomena are quite interesting and align with the ultrafast amorphization of this material.
关键词： elastic stiffness,femtosecond-laser excitation,elastic waves,x-ray diffraction,phase-change material
更新于2025-09-16 10:30:52