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Compensation of Distortions of Polarization Characteristics of Ring Resonators
摘要： The reasons of occurrence of polarization mode distortions and methods of their compensation are investigated. It is demonstrated that sensitivity of lasers with ring resonator to magnetic field may be reduced, if effect of induced polarization anisotropy to be compensated by means of installation of a mirror in resonator in certain position, which complies with the minimum ellipticity angle.
关键词： polarization characteristics of interference mirrors,ring optical resonators,phase anisotropy,information optics
更新于2025-09-23 15:23:52
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Exceptional Two-Photon Absorption in Alkynylruthenium-Gold Nanoparticle Hybrids
摘要： Ruthenium alkynyl “star” complexes with tri(2-thienyl)-, tris(1,2,3-triazolyl)-, or triphenyl-benzene cores stabilize gold nanoparticles (AuNPs). Cyclic voltammetry, transmission electron microscopy, molecular modeling, dynamic light scattering, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy studies are consistent with ca. 5 trithienyl- or triazolyl-benzene-cored star complexes decorating the exterior of each AuNP. The ca. 2.5 nm diameter (by TEM) trithienylbenzene-cored gold nanoparticle hybrids are significantly less absorbing than classical Brust nanoparticles stabilized by 1-dodecanethiol; with femtosecond pulsed radiation, they exhibit exceptionally strong saturable absorption and two-photon absorption across the visible range and into the NIR region (3,000,000 GM at 500 nm, 46,000 GM at 750 nm; 1 GM = 10-50 cm4 s photon-1).
关键词： Gold nanoparticles,nonlinear optics,inorganic materials,metal alkynyl complexes,organometallics.
更新于2025-09-23 15:23:52
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Graded-Index Fluoropolymer Antireflection Coatings for Invisible Plastic Optics
摘要： Plastic optics are used in an ever-expanding range of applications and yet a durable, high performance antireflection (AR) coating remains elusive for this material class. Here, we introduce a sacrificial porogen approach to produce ultralow refractive index nanoporous fluoropolymer AR coatings via thermal co-evaporation of Teflon AF and the small molecule N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine (NPD). Using this approach, we demonstrate a five-layer, step-graded AR coating that reduces the solar spectrum-averaged (400 < λ < 2000 nm) reflectance of acrylic plastic to <0.5% for incidence angles up to 40° and withstands over three months of outdoor rooftop exposure with minimal degradation. A trilayer coating optimized for the visible range yields luminous reflectivity down to ~0.1%, effectively rendering double-side coated acrylic plastic invisible under room lighting conditions. Strong adhesion to most optical plastics, an outstanding combination of mechanical, chemical, and environmental durability, and compatibility with commercial vacuum coating systems should enable this AR technology to find widespread practical use.
关键词： gradient-index,polymer optics,sacrificial porogen,antireflection,nanoporous
更新于2025-09-23 15:23:52
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High resolution mesospheric sodium properties for adaptive optics applications
摘要： Context. The performance of laser guide star adaptive optics (AO) systems for large optical and infrared telescopes is affected by variability of the sodium layer, located at altitudes between 80 and 120 km in the upper mesosphere and lower thermosphere. The abundance and density structure of the atomic sodium found in this region is subject to local and global weather effects, planetary and gravity waves and magnetic storms, and is variable on time scales down to tens of milliseconds, a range relevant to AO. Aims. It is therefore important to characterize the structure and dynamical evolution of the sodium region on small, as well as large spatial and temporal scales. Parameters of particular importance for AO are the mean sodium altitude, sodium layer width and the temporal power spectrum of the centroid altitude. Methods. We have conducted a three-year campaign employing a high-resolution lidar system installed on the 6-m Large Zenith Telescope (LZT) located near Vancouver, Canada. During this period, 112 nights of useful data were obtained. Results. The vertical density profile of atomic sodium shows remarkable structure and variability. Smooth Gaussian-shaped profiles rarely occur. Multiple internal layers are frequently found. These layers often have sharp lower edges, with scale heights of just a few hundred meters, and tend to drift downwards at a typical rate of one kilometer every two to three hours. Individual layers can persist for many hours, but their density and internal structure can be highly variable. Sporadic layers are seen reaching peak densities several times the average, often in just a few minutes. Coherent vertical oscillations are often found, typically extending over tens of kilometers in altitude. Regions of turbulence are evident and Kelvin-Helmholtz instability are sometimes seen. The mean value of the centroid altitude is found to be 90.8 ± 0.1 km. The sodium layer width was determined by computing the altitude range that contains a specified fraction of the returned sodium light. We find a mean value of 13.1 ± 0.3 km for the range containing 95% of the photons, with a maximum width of 21 km. The temporal power spectral density of fluctuations of the centroid altitude is well described by a power law having an index that ranges from ?1.6 to ?2.3 with a mean value of ?1.87 ± 0.02. This is significantly steeper than the value of ?5/3 that would be expected if the dynamics were dominated by Kolmogorov turbulence, indicating that other factors such as gravity waves play an important role. The amplitude of the power spectrum has a mean value of 34+6?5 m2 Hz?1 at a frequency of 1 Hz, but ranges over two orders of magnitude. The annual means of the index and amplitude show a variation that is well beyond the calculated error range. Long-term global weather patterns may be responsible for this effect.
关键词： site testing,atmospheric effects,methods: observational,instrumentation: adaptive optics
更新于2025-09-23 15:23:52
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SPHERE/ZIMPOL high resolution polarimetric imager
摘要： Context. The SPHERE “planet finder” is an extreme adaptive optics (AO) instrument for high resolution and high contrast observations at the Very Large Telescope (VLT). We describe the Zurich Imaging Polarimeter (ZIMPOL), the visual focal plane subsystem of SPHERE, which pushes the limits of current AO systems to shorter wavelengths, higher spatial resolution, and much improved polarimetric performance. Aims. We present a detailed characterization of SPHERE/ZIMPOL which should be useful for an optimal planning of observations and for improving the data reduction and calibration. We aim to provide new benchmarks for the performance of high contrast instruments, in particular for polarimetric differential imaging. Methods. We have analyzed SPHERE/ZIMPOL point spread functions (PSFs) and measure the normalized peak surface brightness, the encircled energy, and the full width half maximum (FWHM) for different wavelengths, atmospheric conditions, star brightness, and instrument modes. Coronagraphic images are described and the peak flux attenuation and the off-axis flux transmission are determined. Simultaneous images of the coronagraphic focal plane and the pupil plane are analyzed and the suppression of the diffraction rings by the pupil stop is investigated. We compared the performance at small separation for different coronagraphs with tests for the binary α Hyi with a separation of 92 mas and a contrast of Δm ≈ 6m. For the polarimetric mode we made the instrument calibrations using zero polarization and high polarization standard stars and here we give a recipe for the absolute calibration of polarimetric data. The data show small (<1 mas) but disturbing differential polarimetric beam shifts, which can be explained as Goos-H?nchen shifts from the inclined mirrors, and we discuss how to correct this effect. The polarimetric sensitivity is investigated with non-coronagraphic and deep, coronagraphic observations of the dust scattering around the symbiotic Mira variable R Aqr. Results. SPHERE/ZIMPOL reaches routinely an angular resolution (FWHM) of 22?28 mas, and a normalized peak surface brightness of SB0 ? mstar ≈ ?6.5m arcsec?2 for the V-, R- and I-band. The AO performance is worse for mediocre (?1.0″) seeing conditions, faint stars mR ? 9m, or in the presence of the “low wind” effect (telescope seeing). The coronagraphs are effective in attenuating the PSF peak by factors of >100, and the suppression of the diffracted light improves the contrast performance by a factor of approximately two in the separation range 0.06″?0.20″. The polarimetric sensitivity is Δp < 0.01% and the polarization zero point can be calibrated to better than Δp ≈ 0.1%. The contrast limits for differential polarimetric imaging for the 400 s I-band data of R Aqr at a separation of ρ = 0.86″ are for the surface brightness contrast SBpol(ρ)?mstar ≈ 8m arcsec?2 and for the point source contrast mpol(ρ)?mstar ≈ 15m and much lower limits are achievable with deeper observations. Conclusions. SPHERE/ZIMPOL achieves imaging performances in the visual range with unprecedented characteristics, in particular very high spatial resolution and very high polarimetric contrast. This instrument opens up many new research opportunities for the detailed investigation of circumstellar dust, in scattered and therefore polarized light, for the investigation of faint companions, and for the mapping of circumstellar Hα emission.
关键词： circumstellar matter,instrumentation: adaptive optics,planetary systems,instrumentation: polarimeters,instrumentation: high angular resolution,instrumentation: detectors
更新于2025-09-23 15:23:52
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AIP Conference Proceedings [Author(s) PROCEEDINGS OF THE 12TH INTERNATIONAL CONFERENCE ON SYNCHROTRON RADIATION INSTRUMENTATION – SRI2015 - New York, NY USA (6–10 July 2015)] - Physical optics simulations with Phase for SwissFEL beamlines
摘要： PHASE is a software tool for physical optics simulation based on the stationary phase approximation method. The code is under continuous development since about 20 years and has been used for instance for fundamental studies and ray tracing of various beamlines at the Swiss Light Source. Along with the planning for SwissFEL a new hard X-ray free electron laser under construction, new features have been added to permit practical performance predictions including diffraction effects which emerge with the fully coherent source. We present the application of the package on the example of the ARAMIS 1 beamline at SwissFEL. The X-ray pulse calculated with GENESIS and given as an electrical field distribution has been propagated through the beamline to the sample position. We demonstrate the new features of PHASE like the treatment of measured figure errors, apertures and coatings of the mirrors and the application of Fourier optics propagators for free space propagation.
关键词： beamline optics,X-rays,XFEL,synchrotron radiation
更新于2025-09-23 15:23:52
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Interfacial adhesion between embedded fibre optic sensors and epoxy matrix in composites
摘要： Fibre optic (FO) sensors are becoming increasingly popular for different applications in structural monitoring. Among their excellent properties, a strong interest for this type of sensors are represented by the possibility of embedding FOs inside composite components. In this case, one of the factors that significantly influence the efficiency of the whole Structural Health Monitoring (SHM) system is the interfacial adhesion between FO sensors and the host material. The main objective of this work is to investigate the interfacial adhesion between embedded fibre optic sensors and epoxy matrix to find the best type of optical fibre to be used in epoxy matrices to produce smart composites. Four types of optical fibres with different diameters and coatings (i.e. polyimide, polyacrylate and ormoceramic) were used. Pull-out tests were carried out and different methods were used to obtain the composite/optical fibre interfacial properties. Finally, an optical microscopy and Scanning Electron Microscopy (SEM) analysis were performed to characterize the fibre/matrix interfaces. It was found that the optical fibre that presented the highest energy required for interface rupture and, consequently, less invasiveness to the host material was the ormoceramic fibre with the smallest diameter.
关键词： Structural health monitoring,Pull-out test,interfacial adhesion,fibre optics sensors
更新于2025-09-23 15:23:52
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Deep hybrid scattering image learning
摘要： A well-trained deep neural network is shown to gain capability of simultaneously restoring two kinds of images, which are completely destroyed by two distinct scattering medias respectively. The network, based on the U-net architecture, can be trained by blended dataset of speckles-reference images pairs. We experimentally demonstrate the power of the network in reconstructing images which are strongly di?used by glass di?user or multi-mode ?ber. The learning model further shows good generalization ability to reconstruct images that are distinguished from the training dataset. Our work facilitates the study of optical transmission and expands machine learning’s application in optics.
关键词： Image processing,di?ractive optics.,machine learning
更新于2025-09-23 15:23:52
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Short-Period Multilayer X-ray Mirrors for “Water” and “Carbon Windows” Wavelengths
摘要： This review paper summarizes and provides an overview of our recent studies related to two types of short-period multilayer X-ray mirrors, W/B4C and Co/C. It deals with the experimental observation of the layer intermixing effects and how they affect the X-ray mirror's optical performance. The paper presents also some examples of using the fabricated X-ray mirrors in focusing and imaging experiments at the working wavelengths 2.48 nm and 4.47 nm.
关键词： Thin Films,Interlayer Interaction,Metal-Carbon Compositions,Short-Period Multilayer Structures,X-ray Multilayer Mirrors,X-ray Optics
更新于2025-09-23 15:23:52
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Rapid tomographic reconstruction through GPU-based adaptive optics
摘要： Large telescopes have important challenges in the near future. Increasing the size of mirrors and sensors suppose not only a design issue, but also new computational techniques are needed to deal with the large amount of data. Adaptive Optics is an essential part of extremely large telescopes, and it uses reference stars and a tomographic reconstructor to compensate the aberrations introduced by the atmosphere during observation. The Complex Atmospheric Reconstructor based on Machine lEarNing (CARMEN) is a tomographic reconstructor based on neural networks which has been used during on-sky observations. In this paper CARMEN will be implemented in two different neural network frameworks, which use a Graphics Processing Unit to improve their performance. To time the training and execution will provide results of which framework is faster for its implementation in a real telescope and will supply new tools to keep improving the reconstruction ability of CARMEN.
关键词： Adaptive Optics,Torch,Neural Networks,TensorFlow
更新于2025-09-23 15:23:52