Large Optical Window Research Articles

Flame dynamics of an injection element operated with LOX/H2, LOX/CNG and LOX/LNG in a sub- and supercritical rocket combustor with large optical access

Hot fire tests were performed using a single-injector research combustor featuring a large optical access window ([Formula: see text] mm) for flame visualisation. Three test campaigns were conducted with the propellant combination of liquid oxygen and hydrogen, liquid oxygen and compressed-natural-gas, as well as liquid oxygen and liquefied-natural-gas at conditions relevant for main- and upper-stage rocket engines. The large optical access enabled synchronised flame imaging using ultraviolet and blue radiation wavelengths covering a large portion of the combustion chamber for various sets of sub- and supercritical operating conditions. Combined with temperature, pressure and unsteady pressure measurements, this data provides a high-quality basis for the validation of numerical modelling. Flame width, length and opening angle as features describing the flame topology were extracted from the imaging. The suitability of flame imaging using ultraviolet and blue radiation wavelengths as qualitative markers of heat release was evaluated. Two-dimensional distributions of the Rayleigh Index were calculated for intervals with and without high-amplitude, self-excited oscillations of the longitudinal acoustic resonance modes. The calculated Rayleigh Index values properly reflect the thermoacoustic state of the chamber, indicating that both types of imaging may be used for qualitative study of thermoacoustic coupling of high-pressure cryogenic flames.

Integrated photonics on the dielectrically loaded lithium niobate on insulator platform

Thin-film lithium niobate on insulator (LNOI) is emerging as one of the promising platforms for integrated photonics due to the excellent material properties of lithium niobate, which includes a strong electro-optic effect, high second-order optical nonlinearity, a large optical transparency window, and low material loss. Although direct etching of lithium niobate has been adopted more widely in recent years, it remains to be seen if it will be adopted in foundry processes due to the incompatibility with standard CMOS fabrication processes. Thus, the scalability of the LNOI platform is currently still limited when compared with other platforms such as silicon photonics. Dielectrically loaded LNOI waveguides may present an alternative. These waveguides have been used to demonstrate a range of optical components with a simplified fabrication process while demonstrating competitive performance. In this contribution, we review the recent progress in dielectrically loaded LNOI waveguides, summarize the advantages and disadvantages of different loading materials, compare the performance of different platforms, and discuss the future of these platforms for photonic integrated circuits.

ε‐Poly‐l‐lysine conjugated gold nanorod probe to monitor antimicrobial activity and mechanism of action by surface‐enhanced Raman spectroscopy

AbstractAntimicrobial peptides have been demonstrated to display an immediate response to a large set of pathogenic activity against viruses, bacteria, and fungi by virtue of their local binding with phospholipid phosphatidylserines to exert cytotoxic effect. Plasmonic nanostructures are particularly appealing in medical diagnostics and therapeutics owing to their biocompatibility and ease of surface modification. The current article reports a development of ε‐poly‐l‐lysine modified gold nanorod (PLL‐AuNR) Raman‐active system that can be used to target pathogenic bacteria along with rapid monitoring of antimicrobial action from environmental samples. Result indicates a remarkable change in Raman enhancement factor from 1.49 × 104 to 2.17 × 107 after addition of Salmonella, Bacillus subtilis, and Escherichia coli bacteria in PLL‐AuNR colloid, enabling a large optical window to monitor the process of pathogenic action. Antimicrobial assay with PLL‐AuNR reveals significantly high cytotoxic values of ~92% in E. coli, ~90% in B. subtilis, and ~87% in Salmonella compared with their respective responses in bare PLL, which shows ~37% in E. coli, ~32% in B. subtilis, and ~27% in Salmonella, which proportionally collaborates with change in surface‐enhanced Raman spectroscopy (SERS) intensity beyond 10 min of incubation time. Major experimental design parameters and possible mechanism that relates unusual plasmonic enhancement and antimicrobial action of PLL‐AuNR system have also been discussed.

Optical properties of combined dynamic thermal dynamicloading optical window

Aiming at the large aperture optical window working in the complex environment such as pressure difference and temperature gradient, a combination scheme of optical window was proposed, which was composed of optical glass and acrylic plate. Based on the thermal-optical analysis, the overall strength and thermal environment of optical window were analyzed and calculated theoretically, and the minimum thickness of optical window glass was obtained. The pressure field and axial temperature field were mapped to three-dimensional structure model by finite element software. The surface shape change and imaging quality evaluation index of 380 mm diameter optical window under different glass thickness were calculated. The simulation results were verified by corresponding environmental tests. The results show that the thickness of large aperture optical window with K9 optical glass as raw material is not less than 32.5 mm under this working environment; when the thickness of optical window is 35 mm, the thermodynamic effect can be ignored. Therefore, the large aperture combined optical window of 35 mm can not only meet the intensity, but also meet the imaging quality requirements of multi-spectral camera, which provides a basis for the design of this kind of window.

Optical and devitrification kinetic studies of chloro-antimonate glasses

In this present work optical and devitrification studies of the synthesized 80 Sb2O3 –10 SrCl2 – 10 CdCl2 glasses were explored. The samples were annealed at temperature 455 °C by the different time range from 10 to 25 min with an interval of 5 min. All the synthesized samples have been characterized by spectroscopic techniques viz., UV–visible transmission, Fourier Transform Infrared transmission and Urbach plot was the complementary for the optical band gap calculation, finally the refractive index of the glass sample has been determined. The synthesized glass sample has a large optical window operating between 361 nm and 7.51 μm and has a high refractive index close to 1.7. The Urbach's plot shows that the optical band gap of the glass sample reaches a higher order value 3.25 eV. Scanning electron microscope (SEM) examination confirms that devitrification obeyed superficial mechanism, when controlled by the specific pre-nucleation process, which is based on self-creation of rough areas and the crystallization diffusion depth. On surface crystals formed in different morphologies like polyhedron; hemispherical (rarely); lath and needle. The progression of crystallization towards the interior is done layer by layer mode (nested lamellae) whereas the contour of the assembly is in a root mode. X-ray diffraction (XRD) pattern shows that the crystalline structure is composed of Valentenite. The kinetic parameters such as crystallization energy (150 kJ/mol) and the Avrami's (n = 3.405) index were calculated according to Chen's and Ozawa's methods. The attractive optical qualities and kinetic parameters indicate that the synthesized glass sample is a good stability against devitrification.

Optimization of SnO2/Ag nanowire transparent hybrid electrodes for optoelectronic applications

Silver nanowire (Ag NW) networks are gaining more interest as promising candidates for the substitution of indium tin oxide (ITO) for top electrodes in optoelectronic devices. In this work we investigated the electrical, optical, structural, and morphological properties of SnO2/Ag NW hybrid film deposited by spray pyrolysis root. We showed that annealing at appropriate temperature improves optoelectronic and morphological properties of the SnO2/AgNWs electrodes; the optimal annealing temperature was 180 °C for 20 min. These annealing conditions allow better homogenization of the nanowires and their welding at the intersection nodes ensuring conduction of the charge carriers along the conductive grid formed of nanowires. The optimized SnO2/AgNWs electrodes have a large optical window covering the near-UV, Vis and IR range, with an average transparency of 85% and a sheet resistance of 6.1 Ω/sq. These optoelectronic performances have led to a merit factor of 2.5 × 10−2 Ω−1 being a competitive performance among the currently developed electrodes that can be promising candidates for applications as a transparent electrodes in optoelectronic devices.

Structural characterization and DFT study of a new optical crystal: 2-amino-3-methylpyridinium-3,5-dinitrobenzoate

A new proton transfer complex was synthesized by the reaction between 2-amino-3-methyl pyridine with 3,5-dinitro benzoic acid in methanol solvent at room temperature. Chemical composition and stoichiometry of the synthesized complex 2-amino-3-methylpyridinium 3,5-dinitrobenzoate (AMPDB) were verified by CHN analysis. The AMPDB crystals were subjected to FT-IR spectral analysis to confirm the functional groups in the compound. UV–Vis–NIR spectral studies revealed that the AMPDB has a large optical transparency window. Single crystal XRD analysis reveals that AMPDB belongs to a monoclinic system with P21/c space group. NMR spectroscopic data indicate the exact carbon skeleton and hydrogen environment in the molecular structure of AMPDB. The thermal stability of the compound was investigated by thermogravimetry (TG). Computational studies such as optimisation of molecular geometry, natural bond analysis (NBO), Mulliken population analysis and HOMO-LUMO analysis were performed using Gaussian 09 software by B3LYP method at 6-311 G(d p) basis set. The first order hyperpolarizability (β) value is 37 times greater than that of urea. The optical nonlinearities of AMPDB have been investigated by Z-scan technique with He-Ne laser radiation of wavelength 632.8 nm. Hirshfeld analysis indicate O⋯H/H⋯O interactions are the superior interactions confirming intensive hydrogen bond net work.

Hydrogen bonded 2-methyl-1H-imidazol-3-ium 3,5-dinitrobenzoate 3,5-dinitrobenzoic acid, a new optical crystal: Evaluation of properties by structural, spectral, quantum chemical calculations, Z-scan and Hirshfeld studies

A new hydrgen bonded proton transfer complex, 2-methyl imidazolium 3, 5-dinitrobenzoate 3,5-dinitro benzoic acid (MIDB) was synthesized by the reaction between 2-methyl imidazole with 3,5-dinitro benzoic acid (1:2) in methanol solvent at room temperature. The crystals were subjected to FT-IR spectral analysis to confirm the functional groups of the new compound. Single crystal XRD analysis reveals that MIDB belongs to monoclinic system with P21/c space group. The asymmetric unit consists of one 2-methyl imidazolium cation, one 3, 5-dinitrobenzoate anion and one uncharged 3,5-dinitro benzoic acid moiety. Experimental NMR spectroscopic data and theoretically calculated NMR data correlated very well to estabilish the exact carbon skeleton and hydrogen environment in the molecular structure of MIDB. The thermal stability of the compound was investigated by thermogravimetry and differential thermal analysis (TG-DTA). Computational studies such as optimization of molecular geometry, natural bond analysis (NBO), Mulliken population analysis and HOMO-LUMO analysis were performed using Gaussian 09 software by B3LYP method at 6–31 g basis set level. The calculated first-order polarizability (β) of MIDB from computational studies is 4.1752 × 10−30 esu, which is 32 times greater than that of urea. UV–vis–NIR spectral studies revealed that the MIDB has a large optical transparency window. The optical nonlinearities of MIDB have been investigated by Z-scan technique with HeNe laser radiation of wavelength 632.8 nm. Hirshfeld analysis indicate O⋯H/H⋯O interactions are the superior interactions confirming excessive hydrogen bond net work in the molecular structure.

Thermal stability and far infrared transmitting property of GeTe4-AsTe3-AgI glasses and glass-ceramics

The present GeTe4-AsTe3-AgI glasses extend the optical window to up to 25μm and its glass-forming region has been explored for practical applications. Their structure, glass-forming ability, thermal stability, infrared transmitting properties were investigated. The results reveal that the GeTe4-AsTe3-AgI glasses exhibit a large glass-forming region situated around the GeTe4-rich domain. Raman analysis confirms the formed [GeTe3I] and [AsTe2I] units are mainly responsible for the improvement in glass-forming ability. The optimum 40GeTe4-30AsTe3-30AgI glasses exhibit a large optical window extending from 2 to 25μm while being stable enough toward crystallization to permit the preparation of fibers and molded lenses. Under proper annealing at 150°C, 40GeTe4-30AsTe3-30AgI glass-ceramics, with high mechanical and thermal properties while still keeping the IR transmittance unchanged, were obtained for the first time.

Aqueous route to color-tunable Mn-doped ZnS quantum dots

Mn-doped zinc sulfide (Mn:ZnS) quantum dots stabilized by 3-mercaptopropionic acid (MPA) were synthesized at 100 °C in basic aqueous solution using the nucleation-doping strategy. The optical properties and structure of the obtained Mn:ZnS QDs have been characterized by UV–vis, photoluminescence (PL) and time-resolved PL spectroscopies, transmission electron microscopy (TEM), X-ray diffraction (XRD), and electron spin resonance (ESR). The obtained nearly monodisperse Mn:ZnS@MPA QDs have an average diameter of ca. 2.5 nm and a zinc-blende crystal structure. By varying the base (LiOH, NaOH, KOH, CsOH) used to deprotonate the MPA ligand and adjust the pH of the aqueous solution to 11, the PL emission wavelengths can be tuned within a relatively large optical window, from 567 to 594 nm. The variations of charge density near the surface of the QDs obtained by changing the cation associated to the MPA ligand and of the dopant location in the ZnS host are at the origin of the PL shifts observed. In order to improve the PL emission efficiency, a ZnS shell was subsequently overcoated around the Mn:ZnS core nanocrystals. With ZnS shell growth, the PL emission wavelength was restricted between 570 and 583 nm but PL quantum efficiency of Mn:ZnS/ZnS core/shell QDs increased up to 18.4%.

Highly Emissive, Color-Tunable, Phosphine-Free Mn:ZnSe/ZnS Core/Shell and Mn:ZnSeS Shell-Alloyed Doped Nanocrystals

High-quality Mn:ZnSe/ZnS core/shell and Mn:ZnSeS shell-alloyed doped nanocrystals (d-dots) with up to 50% photoluminescence (PL) quantum yield (QY) have been synthesized based on nucleation-doping strategy through a phosphine-free approach. The formation of MnSe nanoclusters was achieved by adjusting the ratio of stearic acid to manganese stearate and using a highly reactive Se precursor. Mn: ZnSe/ZnS core/shell d-dots were prepared by an epitaxial ZnS growth on the Mn:ZnSe core. The PL QY of Mn:ZnSe/ZnS core/shell d-dots decreased dramatically after injections of S precursor but was completely recovered through an UV irradiation. After annealing at 240 °C for 30 min, the core/shell Mn:ZnSe/ZnS d-dots evolved to the Mn:ZnSeS shell-alloyed d-dots with high PL QY. The PL peak position of the d-dots could be tuned within a relatively large optical window, from 584 to 605 nm.

ChemInform Abstract: Rare-Earth Doped Fluoride Glass Fibres

Abstract Fluoride glass optical fibres are characterized by a large optical window covering the range 0.4–5 μm which permits excitation and fluorescence spectroscopy in a much more extended domain than with silica-based fibres. The local ligand field acting on the rareearth ions affects the radiative lifetime, phonon relaxation, excited state absorption, and emission peak broadening. Finally, the fibre structure provides excellent optical confinement for observing laser emission in the visible and mid-IR regions at very low threshold power, permitting laser diode pumping. Multiphonon processes are also observed leading to the up-conversion of IR into the visible or UV and making possible the development of new laser sources for optical recording laser printing, optical amplification, medical and optical sensor applications.

Microwave induced center-doping of silver ions in aqueous CdS nanocrystals with tunable, impurity and visible emission

Under microwave radiation, Ag(+)-doped CdS semiconductor nanocrystals with high photoluminescence quantum yield (approximately 58%) and a surprisingly large optical window (480 to 630 nm) are formed controllably using a center-doping strategy and are optimized through a green approach in pure water solution.

Optically transmissive window on ITER port cell door

In the ITER Thomson Scattering Core LIDAR system there are currently three concepts for collecting scattered light from the plasma and delivering it to the diagnostic room. An option to use a broadband mirror in Cassegrain configuration has been explored. In this concept a large optical window, 1.5 m in diameter, is required in the port cell door. This could be manufactured in a number of ways, including using a single thick window or mosaic arrangement with a supporting structure. Challenges associated with this design include maintaining the secondary confinement barrier, withstanding a pressure differential of 0.5 bar across the window in foreseeable fault conditions, and maintaining the optical properties of the window. It must also be possible to protect the window when work is being carried out in the area. Fracture analysis for brittle material was carried out, for a flaw size with a length to depth ratio of 80/20, which gave a safety reserve factor of 4. The flaw size was based on a standard optical transmissive lens for collection light. A static analysis was carried out on both options of having a single thick glass window or a mosaic arrangement. The principal stress for a single window arrangement is 12 MPa and for a proposed mosaic arrangement is 12.5 MPa. The analyses have demonstrated that a single glass window with a thickness of 42 mm would be mechanically acceptable but expensive to manufacture and it would be difficult to polish glass of that size to lens quality. By comparison in the proposed mosaic window arrangement, the glass thickness is reduced by 50% with the aid of the supporting structure. As a result of the supporting structure the geometrical optical losses are 4%, which are mechanically and optically acceptable, whilst significantly reducing the cost of manufacturing.

Efficient and Color-Tunable Mn-Doped ZnSe Nanocrystal Emitters: Control of Optical Performance via Greener Synthetic Chemistry

Formation of Mn-doped ZnSe quantum dots (Mn:ZnSe d-dots) using nucleation-doping strategy was studied systematically and optimized through greener approaches. The resulting d-dots were with high ( approximately 50%) photoluminescence (PL) quantum yield (QY), which was achieved by the controlled formation of small-sized MnSe nanoclusters as the core and a diffused interface between the nanocluster core and the ZnSe overcoating layers. Synthesis of the d-dots under high temperatures (240-300 degrees C) was achieved by varying the structure of the metal carboxylate precursors, concentration of the inhibitors, free fatty acid, and concentration of the activation reagents, fatty amines. Highly emissive d-dots synthesized under desired conditions were found to be extremely stable upon thermal treatment up to the boiling point of the solvent (about 300 degrees C), which was quantitatively studied using in situ measurements. The PL peak of the d-dots was controllably tuned in a surprisingly large optical window, from 565 to 610 nm. These highly emissive and stable d-dots possess characteristics of practical emissive materials, especially for applications requiring high power, high concentration of emitters, and under tough conditions.

Synthesis, growth and characterization of a new nonlinear optical crystal: l-arginine maleate dihydrate

A new nonlinear optical material L-arginine maleate dihydrate, C6H14N4O2,C4H4O4,2H2O (LAMD) was synthesized and single crystals were grown by slow cooling and also by slow evaporation method at constant temperature from its aqueous solution. Quality and size of the crystals are found to be dependent on pH of the solution and best crystals were obtained at pH = 4. Single crystal X-ray diffraction analysis reveal that the crystal lattice of LAMD is triclinic with unit cell parameters a = 5.264(3)Å, b = 8.039(3)Å, c = 9.784(3)Å, α = 106.19(3)°, β = 97.24(3)°, γ = 101.66(2)°. Second harmonic generation efficiency is found to be about 6.8 times that of quartz. It is optically transparent down to 300 nm and possesses a large optical window between 300–2000 nm. The compound is thermally stable up to 93.4 °C. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Developing a fiber-optic probe to combine subcutaneous fat depth and meat quality measurements

This feasibility study demonstrates that the boundary between porcine subcutaneous fat and longissimus muscle can be detected with a probe using optical fibers to illuminate and detect anatomical boundaries. A relatively large optical window (approximately 3 mm2) seemed to give the best resolution of fat to muscle boundaries, whereas a smaller window gave a better resolution of marbling. Scattered, obliquely sectioned optical fibers gave reflectance spectra of fat and muscle that were relatively flat and parallel (fat > muscle). Thus, white light may be used with optical fibers to detect fat to muscle boundaries, although the greatest monochromatic separation was at 820 nm. In comparing measurements made as the probe penetrated the meat with those made as the probe was withdrawn, structures appeared to be deeper on the way in than on the way out, because of compression of the meat. Multichannel operation allowed tissue transmittance to be measured as well as reflectance and channels to be averaged to improve performance. These observations will be useful in developing new apparatus to measure fat depth and meat quality in one operation using optical fibers.

Rare-earth doped fluoride glass fibres

Fluoride glass optical fibres are characterized by a large optical window covering the range 0.4–5 μm which permits excitation and fluorescence spectroscopy in a much more extended domain than with silica-based fibres. The local ligand field acting on the rareearth ions affects the radiative lifetime, phonon relaxation, excited state absorption, and emission peak broadening. Finally, the fibre structure provides excellent optical confinement for observing laser emission in the visible and mid-IR regions at very low threshold power, permitting laser diode pumping. Multiphonon processes are also observed leading to the up-conversion of IR into the visible or UV and making possible the development of new laser sources for optical recording laser printing, optical amplification, medical and optical sensor applications.

Large optical cavity AlGaAs buried heterostructure window lasers

Large optical cavity buried heterostructure window lasers in which only the transparent AlGaAs waveguiding layers, and not the active layer, extend to the laser mirrors have been fabricated. These lasers have threshold currents and differential quantum efficiencies comparable to those of regular large optical cavity buried heterostructure lasers in which the active region extends to the laser mirrors, however the window lasers have been operated under pulsed conditions at three times the power at which otherwise identical lasers without windows degrade by catastrophic mirror damage.

Determination of strains in optical windows of a high-pressure chamber by holographic interferometry and finite element analysis

Holographic interferometry and finite element analysis have been applied to determine the strain in a large optical window installed in a high-pressure chamber. Two different shapes of windows were chosen, and the outside and inside surface strains of the windows were followed as a function of internal pressure by taking double exposed holograms at 69-bar intervals up to 483 bars. The results were compared with the values calculated by a standard finite element code with an assumption of no displacement at the load-bearing edge. The agreement between two results was found to be good for both cases.