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Coupling between plasmonic nanohole array and nanorod arrays: the emerging of a new extraordinary optical transmission mode and epsilon-near-zero property
摘要： The compound Ag nanohole structures with an Ag nanorod in the middle of an Ag nanohole are investigated by finite-difference-time-domain calculations. The structure shows strong polarization-dependent optical properties. A new extraordinary optical transmission (EOT) mode is observed when the polarization direction is aligned with the long axis of the nanorods, and its resonance wavelength red-shifts exponentially with the nanorod length. Around this resonance wavelength, the real part of the effective permittivity also becomes zero, demonstrating the epsilon-near-zero (ENZ) property. The new EOT mode is found to be the result of the enhanced local radiation of the nanorods as well as the electromagnetic coupling to the nanoholes to produce the enhanced transmission. The tunable resonance wavelength, EOT, strong near-field enhancement, and ENZ properties make the structure ideal for many potential applications, such as ultrathin optical filter, polarizers, surface-enhanced spectroscopies, etc.
关键词： tunable transmission,epsilon-near-zero,nanohole array,extraordinary optical transmission,nanorod array
更新于2025-09-23 15:21:01
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Optimization of Transmitter-Side Signal Rotations in the Presence of Laser Phase Noise
摘要： In this paper, we present a 1050-nm electrically pumped microelectromechanically tunable vertical cavity surface-emitting laser (MEMS-VCSEL) with a record dynamic tuning bandwidth of 63.8 nm, suitable for swept-source optical coherence tomography (SS-OCT) imaging. These devices provide reduced cost and complexity relative to previously demonstrated optically pumped devices by obviating the need for a pump laser and associated hardware. We demonstrate ophthalmic SS-OCT imaging with the electrically-pumped MEMS-VCSEL at a 400 kHz axial scan rate for wide-field imaging of the in vivo human retina over a 12 mm × 12 mm field and for OCT angiography of the macula over 6 mm × 6 mm and 3 mm × 3 mm fields to show retinal vasculature and capillary structure near the fovea. These results demonstrate the feasibility of electrically pumped MEMS-VCSELs in ophthalmic instrumentation, the largest clinical application of OCT. In addition, we estimate that the 3 dB coherence length in air is 225 ± 51 m, far greater than required for ophthalmic SS-OCT and suggestive of other distance ranging applications.
关键词： Medical imaging,tunable lasers,optical coherence tomography,micro and nano opto-electromechanical systems (MOEMS),semiconductor lasers
更新于2025-09-23 15:21:01
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The Chicago Water Isotope Spectrometer (ChiWIS-lab): A tunable diode laser spectrometer for chamber-based measurements of water vapor isotopic evolution during cirrus formation
摘要： We describe a new tunable diode laser (TDL) absorption instrument, the Chicago Water Isotope Spectrometer, designed for measurements of vapor-phase water isotopologues in conditions characteristic of the upper troposphere [190–235 K temperature and 2–500 parts per million volume (ppmv) water vapor]. The instrument is primarily targeted for measuring the evolving ratio of HDO/H2O during experiments in the “Aerosol Interaction and Dynamics in the Atmosphere” (AIDA) cloud chamber. The spectrometer scans absorption lines of both H2O and HDO near the 2.64 μm wavelength in a single current sweep, increasing the accuracy of isotopic ratio measurements. At AIDA, the instrument is configured with a 256-m path length White cell for in situ measurements, and effective sensitivity can be augmented by enhancing the HDO content of chamber water vapor by an order of magnitude. The instrument has participated to date in the 2012–2013 IsoCloud campaigns studying isotopic partitioning during the formation of cirrus clouds and in the AquaVIT-II instrument intercomparison campaign. Realized precisions for 1-s measurements during these campaigns were 22 ppbv for H2O and 16 ppbv for HDO, equivalent to relative precisions of less than 0.5% for each species at 8 ppmv water vapor. The 1-s precision of the [HDO]/[H2O] ratio measurement ranged from 1.6‰ to 5.6‰ over the range of experimental conditions. H2O measurements showed agreement with calculated saturation vapor pressure to within 1% in conditions of sublimating ice and agreement with other AIDA instruments (the AIDA SP-APicT reference TDL instrument and an MBW 373LX chilled mirror hygrometer) to within 2.5% and 3.8%, respectively, over conditions suitable for all instruments (temperatures from 204 K to 234 K and H2O content equivalent to 15–700 ppmv at 200 hPa).
关键词： upper troposphere,isotopic ratio measurements,water isotopologues,AIDA cloud chamber,tunable diode laser
更新于2025-09-23 15:21:01
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Selfa??Assembled PMMA Porous Membranes Decorated with In Situ Synthesized ZnO Nanoparticles with UVa??Tunable Wettability
摘要： This study reports a simple approach to fabricate porous poly(methyl methacrylate) (PMMA) membranes homogeneously decorated with exposed zinc oxide (ZnO) nanoparticles (NPs). This fabrication method significantly overcomes the disadvantages of both conventional foaming processes and incorporation of inorganic NPs in polymeric matrices. In particular, the porous structure is simply self-assembled by slowly evaporating a suitable solvent. The ZnO NPs are in situ formed by a thermally activated conversion of the zinc acetate precursor, previously embedded in the polymeric matrix. Scanning and transmission electron microscopy investigations show the formation of the desired self-assembled highly porous structure and ZnO NPs with branched morphology, respectively. The wetting behavior of the membranes surface is studied as a function of the ZnO content and UV irradiation, exploiting the switchable wettability of ZnO. The obtained unexpected results are then tentatively rationalized taking into account the surface chemistry and the roughness that arises from both porous structure and the different NPs dimensions and content.
关键词： porous membranes,nanocomposites,tunable wettability,self-assembly,in situ synthesis
更新于2025-09-23 15:21:01
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Diastereoisomer-Induced Morphology Tunable Self-Assembled Organic Microcrystals of Conjugated Molecules for Ultraviolet Laser
摘要： Precisely controlling self-assembly behavior and micro/nanostructure morphology of conjugated materials is significant for constructing optoelectronic devices. Inspired by natural functional materials, molecular stereoisomerism strategy (MSS) is an effective and convenient means to tune their molecular arrangement and macroscopic property of conjugated materials. Herein, a supramolecular chiral difluorenols, 9,9′-diphenyl-9H,9′H-[2,2′-bifluorene]-9,9′-diol (DPFOH), is set as a desirable model to reveal the diastereomeric effects of conjugated molecules toward controlling the micro/nanostructure morphology and optoelectronic behavior for deep-blue organic laser. Two diastereomers, raceme (rac)- and mesomer (meso)-DPFOH, are obtained and unambiguously elucidated by X-ray crystallography. It is common sense to observe the slight diastereomeric effects on photophysical properties and electrochemical characteristics in solution or pristine film state for the isotropic phase. Interestingly, as a consequent of the disparate multi-dimensional intermolecular interaction, rac-DPFOH molecule can self-assemble into 1D rod-shaped but rectangular plate-shaped microcrystals for meso-DPFOH. Impressively, rac-DPFOH microrod presents a well-defined emission with an excellent ultraviolet microlasing behavior at 398 nm, whereas the 2D microplate of meso-DPFOH show a broad emission centered at 420 nm without gain processing. Therefore, MSS provides a new approach to design conjugated molecules and tune superstructure morphology for optoelectronic applications.
关键词： optical properties,tunable morphology,organic ultraviolet microlasers,diastereoisomer effect,microcrystals
更新于2025-09-23 15:21:01
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Performance Improvement of Gate-Tunable Organic Light-Emitting Diodes with Electron-Transport and Hole-Blocking Layers
摘要： The current density and luminance of gate-tunable organic light-emitting diodes (OLEDs) can be modulated by application of an external gate potential. However, existing gate-tunable OLEDs require further optimization to make them suitable for practical use. In this work, the rapid electron conduction of 4,4’-bis(N-carbazolyl)-1,1’biphenyl (CBP) molecules under low operating potential is demonstrated in polymer electrolyte-coated super yellow (SY) polymer light-emitting diodes (PLEDs). This behavior is attributed to the facile electrochemical n-doping of CBP by the polymer electrolyte infiltrated into the SY PLED through the porous aluminum cathode. The field-modulated conductivity of CBP upon applying an external gate potential to electrolyte-gated (EG) PLEDs is demonstrated. These phenomena lead to the improved performance of EG SY PLEDs with a CBP electron-transport layer and 1,3,5-tris[(3-pyridyl)-phen-3-yl]benzene) (TmpypB) hole-blocking layer between the porous aluminum cathode and SY emissive layer, including low turn-on voltage (1.5 V), low current density leakage (0.01 mA/cm2), low off luminance (<0.01 cd/m2), saturated on-current density (2 mA/cm2) and on-luminance (100 cd/m2), and largely suppressed hysteresis. These results pave the path for practical application of EG OLEDs in displays, especially near-to-eye displays.
关键词： facile electrochemical doping,saturated on-current density and on-luminance,low off-current density leakage and off-luminance,suppressed hysteresis,near-to-eye displays,gate-tunable organic light-emitting diodes,grayscale displaying,porous electrodes
更新于2025-09-23 15:21:01
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Environmentally Stable 1.56-??m Femtosecond Laser System With Discontinuous Selectable Repetition Rate
摘要： We demonstrate here an environmentally stable and compact Er-doped fiber laser system capable of delivering sub-100-fs pulse duration with discontinuous selectable repetition rate from 10 to 70 MHz. This laser source employs a SESAM harmonic mode-locked soliton laser to facilitate tunable repetition rate. A single-mode-fiber (SMF) amplifier and a double-cladding-fiber (DCF) amplifier (both with double-pass configuration) bridged by a three-stage YVO4-based divider are used to manage the dispersion map and boost the seed pulses. With the help of ×8 replicas, the seed pulses are simultaneously amplified and compressed with 90% recombining efficiency, generating 4.60-nJ pulse energy at 10 MHz and 6.13-nJ pulse energy at 70 MHz. The main advantage of the proposed laser system is that when pulse repetition rate is switched on-demand, the pulse duration can be kept almost unchanged only by simply adjusting the pump powers of the fiber amplifiers, instead of changing any optical device (the spacing between gratings or the length of fibers).
关键词： fiber amplifiers,Mode-locked Laser,ultrafast laser,tunable repetition rate
更新于2025-09-23 15:21:01
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Tunable Terahertz Graphene-Based Absorber Design Method Based on a Circuit Model Approach
摘要： In this paper, a simple, fast, and novel method for designing a tunable terahertz absorber with arbitrary central frequency and desired fractional bandwidth is presented. The proposed absorber consists of a single layer periodic array of graphene ribbons (PAGRs), placed a quarter wavelength from a metallic ground, separated by a dielectric material. An analytical circuit model of the terahertz absorber is used to obtain analytical expressions for the input impedance of the proposed device. Then, a simple expression for determining the value of capacitance and the resonance conditions of the RLC circuit is used to achieve a terahertz absorber with arbitrary central frequency and desired fractional bandwidth. The proposed method is applicable for the design of both narrowband and broadband absorbers, with only one layer of graphene ribbons. Also, the presented method is applicable for designing ultra-wideband absorbers using multiple layered PAGRs. Full-wave numerical simulation is performed to verify the accuracy and validity of the presented method. Excellent performance of the proposed method in terms of computation time and memory resource and providing the desired terahertz absorber characteristics shows that our method is promising as a design approach for sensing, imaging and ?ltering applications.
关键词： circuit model,graphene,Terahertz absorber,transmission line method,tunable bandwidth
更新于2025-09-23 15:21:01
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Magnification-invariant surface profiling technique for structured illumination imaging and microscopy
摘要： The structured illumination (SI) surface profiling method that is fast and has a depth-independent image magnification ratio is presented. Utilizing an electrically tunable lens (ETL) makes it possible to scan the object plane rapidly and motionlessly. The change in magnification ratio that generally occurs with the variation in the focal length of an objective lens is minimized by using a 4f relay system and placing the ETL at the confocal plane. The high reflection at the uncoated membrane surfaces of the ETL is bypassed by using polarization optics. It is also proposed that the fast response of the ETL can be fully exploited by switching the scanning sequence from that of a conventional SI imaging system; performing the depth scan before the pattern shift. It is shown that the scanning speed was increased up to 25 times. The principle and the related problems of SI profiling based on an ETL are fully analyzed, and the concept is confirmed experimentally. In the experiment, scanning depth variation of 35 mm could be achieved while keeping the magnification ratio variation below 0.03. The ability of 3D profiling is demonstrated by SI imaging a cone-shape 3D object and a face-shape plaster figure. In the fields requiring fast scanning, such as an intraoral scanner or biomedical imaging, the proposing SI imaging method can be fully utilized.
关键词： Tunable Lens,Surface Profiling,Intraoral scanner,Structured Illumination,Magnification invariant
更新于2025-09-23 15:21:01
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[IEEE 2019 11th Electrical Engineering Faculty Conference (BulEF) - Varna, Bulgaria (2019.9.11-2019.9.14)] 2019 11th Electrical Engineering Faculty Conference (BulEF) - Experimental study of LED luminaire for Human Centric Lighting
摘要： The article examines an experimental installation with a Human Centric Lighting illuminator to find out if new technologies such as Tunable White and Dali Device Type 8 meet the requirements for accurate and smooth change in the radiated color temperature of the illuminator. To this end, a number of real-time measurements have been carried out and analyzed. The measurement results are summarized in the graphs for the illuminator investigated
关键词： Dali Device Type 8 (DT8),LED luminaire,Human Centric Lighting (HCL),Tunable White
更新于2025-09-23 15:21:01