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Evaluation of Silica Nanofluids in Static and Dynamic Conditions by an Optical Fiber Sensor
摘要： This work presents an optical fiber dynamic light scattering sensor capable of simultaneously assessing concentration and flow speed of nanofluids. Silica nanoparticles (189 nm) in water were tested, yielding a sensitivity of 0.78288 × 103 s?1 for static conditions. Then, the sensor was submitted to situations that simulate spatial concentration changes, offering better results than those obtained by traditional mathematical models. Finally, in flow tests, the light backscattered by the nanoparticles were collected by a fiber probe placed parallel to the streamline, whereas intensity values were processed by artificial neural networks. The sensor provides average errors of 0.09 wt% and 0.26 cm/s for concentration and speed measurements, respectively, and can be further applied to assess different types of nanofluids and inline processes.
关键词： silica nanofluid,concentration measurement,optical fiber sensor,flow speed measurement
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) - UV-Grade Silica-Based Photonic Crystal Fibers for Broadband UV Generation over 350–395 nm
摘要： A major challenge in supercontinuum (SC) generation is to overcome the shortcomings of existing fibre-based SC sources in the ultraviolet (UV) wavelength range below 400 nm. There is particular need for broadband sources of UV light in applications such as multi-photon fluorescence microscopy for simultaneous coherent excitation of multiple fluorophores. However, UV generation in conventional silica-core fibres is extremely difficult because of factors such as material absorption, large normal dispersion, glass stability, power handling, and aging, and this has motivated much recent interest in the use of alternative approaches. Although these results show great promise, compatibility with the ubiquitous silica platform remains a problem, and there is thus intense current interest in generating UV-light using modified UV-resistant silica glasses. In this paper, we report the design and fabrication of small-core highly nonlinear UV-grade photonic crystal fiber (PCF) drawn from Heraeus F110 UV-resistant silica glass, and its application to broadband UV generation over 260-400 nm. The few mode PCF is shown in Fig. 1(a) and was designed with: core diameter ~4.24 μm, hole diameter d = 3.5 μm, pitch Λ =3.88 μm, and was designed to support five LP modes in a scalar approximation. The calculated dispersion coefficients and mode profiles are shown in Figs 1(b) and (c). Figure 1(d) and (e) show experimental results pumping with picosecond laser pulses at 355 nm. For a 1m length of the PCF, we observe intermodal four-wave mixing (FWM) peaks with Fig. 1(d) showing a series of spectra as the output power varies from 0.1 – 0.2 mW. The FWM peaks are generated over the range 350-370 nm and the peak positions are in good agreement with calculations based on the fibre modal characteristics. For a longer 3 m fibre length, intermodal FWM is not observed, but rather we see cascaded Raman scattering out to 6th-order over the range 355-395 nm. The UV-emission was observed to have stable 0.3 mW output power without any detrimental photo-darkening. In this paper, we have reported the fabrication of highly nonlinear photonic crystal fiber from UV-grade glass and experimentally demonstrate nonlinear frequency conversion over 350-395 nm by pumping at 355 nm with picosecond laser pulses. These results represent an important step towards efficient UV supercontinuum generation in an all-silica fiber platform.
关键词： nonlinear frequency conversion,broadband UV generation,supercontinuum generation,UV-grade silica-based photonic crystal fibers,UV-resistant silica glass
更新于2025-09-12 10:27:22
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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) - Effective Coupling of a Plasmonic Nanorod to a Microsphere Resonator
摘要： Coupled photonic-plasmonic systems have already proven successful as ultra-sensitive sensors with the potential of single virus detection. Such systems are e.g. composed of a plasmonic nanoparticle in vicinity of an optical resonator usually in the form of a microsphere, a mirroring or a microdisk. These systems are proven highly sensitive due to their large quality factor and are thus utilized as bio, pressure, gas or temperature sensors. When a plasmonic nanoparticle is positioned near such resonator, coupling of the plasmonic and photonic modes can result in an ultra-sensitive biosensor, since nanoparticle presence enhance ambient refractive index (RI) variation sensitivity. In this paper, photonic-plasmonic coupling of a gold nanorod in close vicinity of a silica microsphere is simulated in order to investigate various types of coupling settings in such systems. The presence of the nanorod results in a frequency shift as well as in a reduction of the quality factor, which are both highly dependent on nanorod properties such as size, distance between the particle and the sphere as well as the nanorod orientation relative to the sphere surface. A single gold nanorod is positioned in 50nm distance to a 15.5μm silica microsphere which supports a whispering gallery mode at 1550nm and both resonance frequency and quality factor are computed using the simulation platform COMSOL Multiphysics. The nanorod orientation is altered starting from the tangential direction with respect to the sphere surface (0o) to the perpendicular direction (90o). In the Fig 1a) the quality factor together with the damping constant is shown as a function of the nanorod orientation for at an operating wavelength of 1550nm. The 90o direction results in higher quality factor as well as a better mode stability although the frequency shift associated to a 90o turn is only about 10GHz. In Fig 1b) the frequency shift and quality factor for the perpendicular nanorod versus ambient medium RI is plotted, which confirms the ultra-sensitivity of the designed optical resonator up to a 10-3 RI shift. The electric field distribution outside and inside of the nanorod is illustrated in Fig. 1c) for the three directions 90o, 45o and 0o where the perpendicular nanorod shows the weakest interaction with the excited whispering gallery mode and thus yields the largest quality factor.
关键词： silica microsphere,photonic-plasmonic coupling,gold nanorod,COMSOL Multiphysics,whispering gallery mode
更新于2025-09-12 10:27:22
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From statistic to deterministic nanostructures in fused silica induced by nanosecond laser radiation
摘要： The production of structures by laser machining below the diffraction limit is still a challenge. However, self-organization processes can be useful. The laser-induced self-organized modification of the shape of photolithographic produced chromium structures on fused silica as well as the structuring of the fused silica surface by nanosecond UV laser radiation was studied, respectively. Low fluence single pulse laser irradiation (? > 300 mJ/cm2) cause the formation from chromium squares to droplets due to the mass transport in the molten chromium film. This process is governed by the instability of the molten metal due to the surface tension driven liquid phase mass transport. For a chromium pattern size similar to the instability length two specific droplet distributions were found which are single droplets with a determined position near the centre of the original pattern or random distributed smaller droplets arranged circularly. Each of the metal patterns can be transferred into the fused silica by a multi-pulse irradiation. The experimental results can be simulated well for low fluences by sequential solving the heat and Navier-Stokes equation.
关键词： fused silica,nanostructuring,nanosecond laser,IPSM-LIFE
更新于2025-09-12 10:27:22
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Plasma formation and relaxation dynamics in fused silica driven by femtosecond short-wavelength infrared laser pulses
摘要： Laser-induced plasma formation and subsequent relaxation in dielectric solids is the precursor to structural modi?cations serving as the basis for direct laser writing of functional optical micro- and nanostructures. Based on an experimental arrangement combining a time-resolved transmission measurement with a cross-phase modulation measurement, we isolate the plasma formation and relaxation dynamics in the bulk of amorphous fused silica excited by femtosecond short-wavelength infrared (k ? 2100 nm) laser pulses. Whereas the relaxation time of the generated subcritical electron-hole plasma was so far assumed to be constant, our ?ndings indicate an intensity-dependent relaxation time. We attribute this intensity dependence to vibrational activation of the medium, leading to detrapping of trapped carriers and a reduced trapping probability.
关键词： plasma formation,femtosecond laser pulses,relaxation dynamics,fused silica,short-wavelength infrared
更新于2025-09-12 10:27:22
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Photo-induced generation of size controlled Au nanoparticles on pure siliceous ordered mesoporous silica for catalytic applications
摘要： A versatile in situ photochemical reduction approach was used to generate a composite of gold nanoparticles and pure siliceous SBA-15 silica support with regular mesopores. The mesoporous silica support was first synthesized and, after calcination, was suspended in a solution of gold bromide (EtOH or H2O) containing a free radical generator activated by UV irradiation and used for the photochemical reduction of gold precursor. The influence of gold precursor concentration, light intensity and nature of the solvents on the formation and properties of gold nanoparticles (size, dispersion, stability) on the mesoporous SBA-15 support have been studied with the aim of optimizing the dispersion of the gold nanoparticles in the mesoporous network and their chemical stability. The catalytic activity of the resulting AuNPs@SBA-15 nanocomposite was successfully evaluated for the oxidation of benzyl alcohol reaction in liquid-phase.
关键词： Benzyl alcohol,Photoreduction,Gold nanoparticles,Mesoporous silica,SBA-15,Oxidation
更新于2025-09-12 10:27:22
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Structural evolution of fused silica below the glass-transition temperature revealed by in-situ neutron total scattering
摘要： The common belief that glass structure is completely frozen-in at room temperature is challenged at both macroscopic and atomic scales. Here, we demonstrate an analytical method to elucidate the fine details of a continuous structural change of fused silica (FS) at temperatures below the glass-transition temperature using in-situ neutron total scattering. We find that the SiO4 tetrahedron expands through the entire temperature range with a local coefficient of thermal expansion of 9.1 × 10?6 K?1, while the average medium-range distance, derived from the first sharp diffraction peak of the structure factor, expands at a rate of 21 × 10?6 K?1. Such an expansion difference reflects glass-structure changes within the "rigid-unit mode" model, where each tetrahedron behaves as a rigid unit and the flexible rotations between rigid units lead to more than two times higher medium-range thermal expansion. We further demonstrate that such rotations change the shape of individual rings, leading to a measurable change in the first sharp diffraction peak (FSDP). This study paves the way to measure the structural changes of other silicate glasses, especially through the glass transition.
关键词： Structural change of fused silica,Short- and medium-range structure,In-situ neutron total scattering,First sharp diffraction peak,Rigid-unit mode
更新于2025-09-12 10:27:22
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Dumbbell–Like Silica Coated Gold Nanorods and their Plasmonic Properties
摘要： Silica coated gold nanorods with dumbbell-like morphology allowing dual functionalization in an individual nanostructure have attracted great attention for applications such as sensing and biological imaging. We report a detailed study on the feasibility of controlling the morphology of silica coating on gold nanorods. The morphology of the silica shell can be either cylindrical or dumbbell shaped. The morphology of the silica shell can be either cylindrical or dumbbell shaped. With constant GNR concentration, the ratio of CTAB and TEOS concentration is the key to determine the amount of available TEOS for silica deposition on GNR since the TEOS will diffuse towards the surface of GNRs. The effect of morphologies on surface-enhanced Raman scattering (SERS) performance was also investigated and we found that the dumbbell morphology of silica coated gold nanorods has the most significant SERS enhancement. Our study is significant in terms of the capability to control the dumbbell morphology of silica coated gold nanorods, which can eventually broaden the application of these plasmonic nanomaterials.
关键词： SERS,TEOS,plasmonic properties,dumbbell-like morphology,CTAB,Silica coated gold nanorods
更新于2025-09-12 10:27:22
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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) - Supercontinuum Generation in a As <sub/>2</sub> S <sub/>3</sub> -Silica Nanospike Waveguide Pumped by Tm-Doped Fiber Laser
摘要： The development of compact bright supercontinuum (SC) sources is of particular interest, especially in the mid-IR where is a lack of suitable sources [1,2]. Here we report first results on SC generation in a As2S3-silica dual nanospike waveguide [3, 4] pumped in different multi-pulse regimes by a high-power femtosecond Tm-doped fiber laser mode-locked by nonlinear polarization evolution [5-7]. The experimental set-up is sketched in Fig. 1a. The central wavelength of the laser is 1890 nm and its repetition rate is 13 MHz. By tuning the polarization controllers (PC1 and PC2) in the ring cavity [8], the laser could be configured to operate in different multi-pulse regimes, namely noise-like pulses, soliton bunches and soliton “rain”. The pulse duration is 931 fs in both soliton regimes. The coherence time of the noise-like pulses is 228 fs. The pulses were free-space launched into the As2S3-silica dual nanospike waveguide designed to improve the launch efficiency in and out of the waveguide (~20%). The central uniform portion of the hybrid nanospike has a core diameter of 1.1 μm, the group velocity dispersion (GVD) curve of which is plotted in the inset of Fig. 1a. The pump wavelength is in the anomalous dispersion region between two zero dispersion wavelengths. The measured SC spectra are shown in Fig. 1b for the regimes of soliton bunches (top) and noise-like pulses (bottom). The results from the soliton “rain” regime (not shown here) and the soliton bunches regime are similar. In the soliton regime, sidebands originating from self-phase modulation are observed for a launched peak power of ~90 W, with the spectrum spanning from 1650 nm to 2200 nm. The launched peak power of the solitons was estimated by the pulse duration and the laser characteristics after taking into account the coupling efficiency. The black-dashed line in Fig. 1b plots the simulated spectrum at the output end of the dual nanospike, agreeing reasonably well with experiment. In the preliminary simulation, a single pulse with the same peak power (90 W) was launched into the model. When pumping the waveguide by noise-like pulses the spectrum barely broadens, probably due to the smaller peak power of a single pulse in the packet. In summary, we have achieved spectral broadening in a As2S3-silica hybrid waveguide pumped in different multi-pulse regimes at 1890 nm. It appears that soliton-like regimes are preferable for SC generation. The system is promising for realizing all-fiber broadband SC sources using well-defined femtosecond pulses, as well as investigating different mechanisms of SC generation in multi-pulse regimes.
关键词： mid-IR,Tm-doped fiber laser,supercontinuum generation,As2S3-silica nanospike waveguide,multi-pulse regimes
更新于2025-09-12 10:27:22
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A Monolithic Gimbal Micro-Mirror Fabricated and Remotely Tuned with a Femtosecond Laser
摘要： With the advent of ultrafast lasers, new manufacturing techniques have come into existence. In micromachining, the use of femtosecond lasers not only offers the possibility for three-dimensional monolithic fabrication inside a single optically transparent material, but also a means for remotely, and arbitrarily, deforming substrates with nanometer resolution. Exploiting this principle and combining it with flexure design, we demonstrate a monolithic micro-mirror entirely made with a femtosecond laser and whose orientation is tuned in a non-contact manner by exposing some part of the device to low energy femtosecond pulses. Given the non-contact nature of the process, the alignment can be very precisely controlled with a resolution that is many orders of magnitude better than conventional techniques based on mechanical positioners.
关键词： femtosecond laser machining,tunable optics,repositioning,integrated optics,monolithic,micro-optics,non-contact,fused silica,flexures
更新于2025-09-12 10:27:22