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Plasmonics of regular shape particles, a simple group theory approach
摘要： A simple hand calculation method based on group theory is proposed to predict the near field maps of finite metallic nanoparticles (MNP) of canonical geometries: prism, cube, hexagon, disk, sphere, etc. corresponding to low order localized surface plasmon resonance excitations. In this article, we report the principles of the group theory approach and demonstrate, through several examples, the general character of the group theory method which can be applied to describe the plasmonic response of particles of finite or infinite symmetry point groups. Experimental validation is achieved by collection of high-resolution subwavelength near-field maps by photoemission electron microscopy (PEEM) on a representative set of Au colloidal particles exhibiting either finite (hexagon) or infinite (disk, sphere) symmetry point groups.
关键词： hexagon,disk,photoemission electron microscopy (PEEM),group theory,sphere,surface plasmon resonance
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Difference-frequency generation in the cavity of a dual-wavelength semiconductor disk laser: Effect of absorption of the short-wavelength radiation in the a??long-wavelengtha?? active region on the operation point stability
摘要： A difference-frequency generation in the external cavity of a dual-wavelength semiconductor disk laser (SDL) is numerically studied. The dual-wavelength SDL itself has been designed to emit two optical beams simultaneously – the short-wavelength beam (usually referred to as the pump) and the long-wavelength beam (signal). The study is performed with the help of the mathematical model based on a set of ordinary differential equations with a time delay. The model takes into account possible absorption of the pump radiation in the active region designed to provide gain for the signal. The steady state operation point, its stability, and transient dynamics of intra-cavity difference-frequency generator (ICDFG) are analyzed. As the pump radiation absorption exceeds the critical value, the operation point is shown to lose the stability within the certain interval of the primary pomp power. The steady-state instability of the ICDFG develops to the multi-scaled oscillations of high amplitude.
关键词： semiconductor disk laser,difference-frequency generation,intracavity nonlinear optical interaction
更新于2025-09-23 15:19:57
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Thermal Infrared Imaging of MWC 758 with the Large Binocular Telescope: Planetary-driven Spiral Arms?
摘要： Theoretical studies suggest that a giant planet around the young star MWC 758 could be responsible for driving the spiral features in its circumstellar disk. Here, we present a deep imaging campaign with the Large Binocular Telescope with the primary goal of imaging the predicted planet. We present images of the disk in two epochs in the L′ filter (3.8 μm) and a third epoch in the M′ filter (4.8 μm). The two prominent spiral arms are detected in each observation, which constitute the first images of the disk at M′, and the deepest yet in L′ (ΔL′ = 12.1 exterior to the disk at 5σ significance). We report the detection of an S/N ～ 3.9 source near the end of the Southern arm, and, from the source’s detection at a consistent position and brightness during multiple epochs, we establish a ～90% confidence-level that the source is of astrophysical origin. We discuss the possibilities that this feature may be (a) an unresolved disk feature, and (b) a giant planet responsible for the spiral arms, with several arguments pointing in favor of the latter scenario. We present additional detection limits on companions exterior to the spiral arms, which suggest that a ?4 MJup planet exterior to the spiral arms could have escaped detection. Finally, we do not detect the companion candidate interior to the spiral arms reported recently by Reggiani et al., although forward modeling suggests that such a source would have likely been detected.
关键词： planets and satellites: formation,stars: pre-main sequence,planets and satellites: detection,planet–disk interactions
更新于2025-09-19 17:13:59
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Artificial Intelligence to Detect Papilledema from Ocular Fundus Photographs
摘要： BACKGROUND Nonophthalmologist physicians do not confidently perform direct ophthalmoscopy. The use of artificial intelligence to detect papilledema and other optic-disk abnormalities from fundus photographs has not been well studied. METHODS We trained, validated, and externally tested a deep-learning system to classify optic disks as being normal or having papilledema or other abnormalities from 15,846 retrospectively collected ocular fundus photographs that had been obtained with pharmacologic pupillary dilation and various digital cameras in persons from multiple ethnic populations. Of these photographs, 14,341 from 19 sites in 11 countries were used for training and validation, and 1505 photographs from 5 other sites were used for external testing. Performance at classifying the optic-disk appearance was evaluated by calculating the area under the receiver-operating-characteristic curve (AUC), sensitivity, and specificity, as compared with a reference standard of clinical diagnoses by neuro-ophthalmologists. RESULTS The training and validation data sets from 6779 patients included 14,341 photographs: 9156 of normal disks, 2148 of disks with papilledema, and 3037 of disks with other abnormalities. The percentage classified as being normal ranged across sites from 9.8 to 100%; the percentage classified as having papilledema ranged across sites from zero to 59.5%. In the validation set, the system discriminated disks with papilledema from normal disks and disks with nonpapilledema abnormalities with an AUC of 0.99 (95% confidence interval [CI], 0.98 to 0.99) and normal from abnormal disks with an AUC of 0.99 (95% CI, 0.99 to 0.99). In the external-testing data set of 1505 photographs, the system had an AUC for the detection of papilledema of 0.96 (95% CI, 0.95 to 0.97), a sensitivity of 96.4% (95% CI, 93.9 to 98.3), and a specificity of 84.7% (95% CI, 82.3 to 87.1). CONCLUSIONS A deep-learning system using fundus photographs with pharmacologically dilated pupils differentiated among optic disks with papilledema, normal disks, and disks with nonpapilledema abnormalities.
关键词： optic-disk abnormalities,fundus photographs,deep-learning system,artificial intelligence,papilledema
更新于2025-09-19 17:13:59
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Subaru Near-infrared Imaging Polarimetry of Misaligned Disks around the SR 24 Hierarchical Triple System
摘要： The SR 24 multistar system hosts both circumprimary and circumsecondary disks, which are strongly misaligned with each other. The circumsecondary disk is circumbinary in nature. Interestingly, both disks are interacting, and they possibly rotate in opposite directions. To investigate the nature of this unique twin disk system, we present 0 1 resolution near-infrared polarized intensity images of the circumstellar structures around SR 24, obtained with HiCIAO mounted on the Subaru 8.2 m telescope. Both the circumprimary disk and the circumsecondary disk are resolved and have elongated features. While the position angle of the major axis and radius of the near-IR (NIR) polarization disk around SR 24S are 55° and 137 au, respectively, those around SR 24N are 110° and 34 au, respectively. With regard to overall morphology, the circumprimary disk around SR 24S shows strong asymmetry, whereas the circumsecondary disk around SR 24N shows relatively strong symmetry. Our NIR observations confirm the previous claim that the circumprimary and circumsecondary disks are misaligned from each other. Both the circumprimary and circumsecondary disks show similar structures in 12CO observations in terms of its size and elongation direction. This consistency is because both NIR and 12CO are tracing surface layers of the flared disks. As the radius of the polarization disk around SR 24N is roughly consistent with the size of the outer Roche lobe, it is natural to interpret the polarization disk around SR 24N as a circumbinary disk surrounding the SR 24Nb–Nc system.
关键词： Misaligned Disks,Polarimetry,SR 24,Near-infrared,Circumprimary Disk,Circumsecondary Disk
更新于2025-09-16 10:30:52
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Milliwatt-Class MHz Repetition-Rate THz Source Driven by a sub-100 fs High Power Thin-Disk Laser
摘要： We demonstrate optical rectification in GaP crystals thin-disk oscillator, nonlinearly driven by a 100 W-class compressed to sub-100 fs in a multi-pass cell. In optimized conditions, we obtain a power of 1.35 mW, which is the highest average power achieved in GaP so far. Additionally, we explore the effect of temperature of the crystal down to 77 K, showing that controlling the temperature of the crystal could be a key aspect for further power scaling and for handling thermal effects that become important at such high driving powers.
关键词： thin-disk laser,optical rectification,THz source,GaP crystals,high power
更新于2025-09-16 10:30:52
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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) - High-Power 0.33 mW Broadband THz Source Driven by an Ultrafast Yb-Based Thin-Disk Laser Oscillator
摘要： THz-time-domain spectroscopy (THz-TDS) is a well-established tool for characterizing material properties and investigating dynamics of complex molecular systems. As the broadband THz generation typically relies on sub-100-fs laser pulses, most systems are currently driven by Ti:sapphire lasers. In the last years there has been a strong effort to replace Ti:sapphire systems with power-scalable Yb-based directly diode-pumped solid-state lasers (DPSSLs). Ultrafast DPSSLs generate higher average power with lower complexity and better efficiency. However, their potential for high-power broadband THz operation has not yet been fully exploited. This study shows the high potential of TDL oscillator driven systems for high-power broadband THz generation. Thanks to the power scalability of the TDL technology we expect broadband THz sources operating at MHz repetition rates and several mW average power to be soon within reach.
关键词： THz-time-domain spectroscopy,thin-disk laser oscillator,broadband THz generation,Yb-based lasers
更新于2025-09-16 10:30:52
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Parametric Analysis of High Power Disk Laser Welding of 5052-H32 Aluminium Alloy
摘要： High power disk laser conducting welding of 2 mm thick AA 5052-H32 was performed within a process window and optimized for improved weld quality (i.e. penetration depth). The macrostructure of the weldment was investigated for the weld penetration depth at varying processing parameters using stereo zoom optical microscopy. The significance of the single effects and interaction effects of the parameters on the weld penetration depth was determined using ANOVA. Maximum weld penetration depth (1.71 mm) was achieved at laser power of 2600 W, welding speed of 0.03 m/s and focal position of -3.75 mm. At 95% confidence, only the welding speed –focal position interaction was found to contribute significantly to the weld penetration depth. The effect of the welding speed was most noticeable at low focal position (F < -3.9), that is, when the workpiece is further away from the focus. A linear regression mathematical model predicting the penetration depth of AA 5052-H32 disk laser weldments to an accuracy of 86% was developed and validated.
关键词： AA 5052-H32 Aluminium Alloy,Optimisation,Regression Model,Disk Laser Welding,ANOVA,Penetration Depth
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE International Conference on Microwaves, Antennas, Communications and Electronic Systems (COMCAS) - Tel-Aviv, Israel (2019.11.4-2019.11.6)] 2019 IEEE International Conference on Microwaves, Antennas, Communications and Electronic Systems (COMCAS) - Terahertz Range Elementary Dipole Excitation of a Thin Dielectric Disk Sandwiched between Two Graphene Covers: Integral Equation Analysis
摘要： We study, using the integral equation technique, the scattering of the field radiated by an elementary dipole, by a thin dielectric disk sandwiched between two conformal graphene covers, on the top and bottom faces. To build a mathematical model of such scatterer, we use the generalized boundary condition in the form first obtained by Mitzner and Bleszynski et al. and generalized by Karlsson. This enables us to derive dual integral equations in the disk plane for the Hankel transforms of the tangential electric and magnetic field components, and cast it to a set of two coupled Fredholm second-kind integral equations. The latter equations are discretized and solved numerically with the guaranteed convergence. We compute and plot the power radiated by an elementary magnetic dipole placed above such a composite disk, in the THz range. This reveals that the studied scatterer is a complicated open resonator supporting the low-frequency plasmon modes and the high-frequency dielectric-disk modes.
关键词： generalized boundary condition,radiated power,thin disk,graphene,plasmon resonances
更新于2025-09-16 10:30:52
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High-Brightness and High-Power Laser Welding of Powder Metallurgy Shape Memory Alloy: Welding-Parameter-Dependent Microstructure
摘要： Despite the growing interest in using powder metallurgy shape memory alloys, there is limited research on their joining and welding aiming to expand their applications. In this research, we utilized a high-power, high-brightness disk laser welding process to join spark-plasma-sintered Ti-51 at.% Ni shape memory alloy and studied the primary factors that affect the strength and functionality of the created sound welds such as intermetallics and martensite (B19￠) phase formation. The introduction of high-power laser could impede the formation of B19￠ and undesirable intermetallics such as TiNi3 and Ti2Ni; however, the desired Ti3Ni4 would also be suppressed and post-weld heat treatment was necessary to induce them again. The microstructure of fusion zones was significantly altered, producing coarse columnar grains with centerline and equiaxed weld centers. Additionally, high-power laser welding of powder metallurgy Ti-Ni alloy triggered amorphous phase formation in the welds due to rapid cooling. It was found that a laser power of 3 kW and welding speed of 6 m/min are optimal welding parameters, since the produced weld solidified along favorable [001] direction of strain recovery in Ti-Ni shape memory alloys.
关键词： disk laser welding,microstructural characterization,shape memory alloys,spark plasma sintering
更新于2025-09-16 10:30:52