Blocking Filter Research Articles

MBE-grown ZnTe epitaxial layer based broadband photodetector with high response and excellent switching characteristics

Zinc telluride (ZnTe) epitaxial layers were grown on gallium arsenide (GaAs) (211) substrate at different growth temperatures by molecular beam epitaxy. The fabricated interdigitated metal semiconductor metal configuration-based photodetector (PD) on ZnTe epitaxial layers exhibited a stable and excellent photo response in a broad spectral range (250–550 nm) up to 125 °C. The room temperature and higher temperature (125 °C) values of maximum current, spectral responsivity and detectivity at an applied bias of 5 V and 550 nm wavelength were 3.5 × 10−8 A, 0.1 A W−1 and 1 × 1011 Jones and 1.7 × 10−6 A, 2.5 A W−1 and 1.5 × 1011 Jones, respectively. The maximum photo-to-dark-current ratio (PDCR) value at zero bias and 100 °C was obtained for the ZnTe layer grown at an optimum growth temperature of 380 °C. The high PDCR value exhibits the self-powered capability of the detector. Furthermore, the detector exhibits good on–off switching to the illuminating light with rise and decay times less than 0.29 s and 0.4 s, respectively, at room temperature. The dependence of the photo response on material quality was analysed by varying the substrate growth temperature. The broadband responsivity of the ZnTe-based PD shows its capability as a multicolour detector in the UV and visible region with the use of suitable blocking filters.

Effects of Fuel Hydrochloric Acid Contamination on Selected Metals

Chlorinated organic compounds, as contaminants in marine fuels, have caused severe damage, affecting both main and auxiliary engines. Contaminated fuels can cause serious damage to an engine and its components, corroding fuel pumps and blocking filters, for example. This affects the operation of the engine, and, in the most severe cases, vessel safety. This study considered fossil diesel containing hydrochloric acid as a possible product formed under certain conditions in fuel contaminated with COCs and its effects on carbon steel, stainless steel, tempering steel, and aluminum. Five fuel samples with different concentrations of hydrochloric acid were prepared, plus one sample of diesel and water. Metal bars were partially immersed in the fuel samples and stored at room temperature for approximately one month. A visual assessment found corrosion across the entire surface of all metal bars when exposed to fuel samples containing hydrochloric acid. Even the smallest acid content (25 ppm) caused corrosion, and the effects were already observable after only two days of exposure. Despite their acid contamination, the measured fuel properties fulfilled the standard for automotive fuels at the beginning of the test. The water in the diesel sample did not cause any visible corrosion.

Tailoring the optical properties of dye–polymer composite films based on polyvinyl alcohol doped with phenol red toward flexible optoelectronic applications

The composite films of polyvinyl alcohol (PVA) incorporating varying concentrations of phenol red (PR) dye were fabricated using the solution casting method. Structural characteristics of the prepared films were explored through XRD and FTIR spectroscopy analyses. The inclusion of PR dye within the PVA matrix induced cross-linking, enhancing the amorphous nature of the doped PVA samples, as evidenced by XRD patterns. In the presence of PR dopants, the FTIR peaks for PVA exhibited altered intensities and increased width, indicating physical interactions between the functional groups of PVA and PR dopants. The impact of PR additives on the optical properties of PVA was investigated across the spectral range of 190–2500 nm. The PVA/phenol red composite demonstrated enhanced UV blocking in the 190–400 nm wavelength range, rendering it suitable for applications such as UV notch filters, including laser blocking filters. The indirect and direct optical band-gaps of PVA polymer films were reduced from 5.20 eV and 5.78 eV to 4.30 eV and 5.28 eV, respectively, with an increase in the PR filling ratio from 0 wt% to 1.8 wt%. The dispersion region of the refractive index was analyzed using the single oscillator model (Wemple-DiDomenico). Calculation and discussion of values such as dispersion and oscillation energies (Ed and Eo), permittivity at infinite frequency (ε ∞), and lattice contribution to the dielectric function (ε L) of PVA/PR composite films were conducted. These advancements position PVA/PR composite films for potential applications in flexible optoelectronic devices, including light-emitting diodes and photodetectors.

Reststrahlen band infrared damping, microwave transparent AlN/polymeric film filters

The low-temperature (t ≈ 20–30 °C) technology of hybrid helicon-arc ion-plasma deposition to grow the amorphous AlN layers on polymeric substrates for getting the IR blocking filters was used. Flexible substrates based on Mylar, Polyethylene Terephthalate/BaSO4 filling and Teflon polymeric films were applied to grow the AlN layers having the Reststrahlen Band at λ∼11–17 μm for filters, which are damping the IR radiation in this spectral region. The Polyvinyl chloride polymeric films without coatings and the Mylar/AlN structures were used to make composed damping filters for spectral range λ∼7.5–25 μm. The transparency of such composed filters in the spectral range λ ∼7.5–25 μm can suppress about 96–98 % of radiation from the objects being at t ∼310 K. In this spectral range, the objects radiate ∼75 % of the total radiated power from a black body in the full EM band spectra. An explanation of the behavior's peculiarities of the spectral dependences of the IR reflectance of polymeric films/AlN structures with using the classical dielectric function model was proposed. The transparency of all polymeric/AlN structures in the microwave frequency range (ν = 60–270 GHz) gains T ≥ 80–90 %.

Multi-technique investigation of silicon nitride/aluminum membranes as optical blocking filters for high-energy space missions

Multi-technique investigation of silicon nitride/aluminum membranes as optical blocking filters for high-energy space missions

Study on optical blocking filter with Mg seed layer for soft X-ray space detection

In the field of X-ray space detection, the optical blocking filter which can transmit X-ray and block UV, visible and infrared light is required. The combination of polyimide film and Al coating is the most commonly used design of OBF. The Al island structure created during magnetron sputtering deposition affects the optical properties of OBF. In this work, the potential of Mg as a seed layer to improve the optical performance of OBF was investigated. Polyimide films coated with Mg–Al bilayer with different thickness parameters (the total thickness was the same, equaled to 80 nm) were prepared, and the effect of Mg on the optical properties of optical blocking filters was analyzed. The results show that the island structure of the Al coating is weakened by the addition of Mg seed layer. For optical blocking filter with 10 nm and 20 nm Mg seed layer, the UV, visible and infrared transmittance decreased significantly, and the X-ray transmittance increased slightly. The blocking performance of UV, visible and infrared light has no change with the variation of storage time.

Short-Wavelength Light-Blocking Filters and Oral Melatonin Administration in Patients With Retinitis Pigmentosa: Protocol for a Randomized Controlled Trial.

The medical community is beginning to recognize that retinitis pigmentosa (RP), due to its disabling progression, eventually leads to a reduction in the patient´s quality of life, a direct economic impact, and an increase in the burden on the health care system. There is no curative treatment for the origin of the disease, and most of the current interventions fail in reducing the associated negative psychological states, such as anxiety and depression, which lead to increased variability of vision and pose a continuous threat to the patient's independence. The aim of this study is to assess the effect of oral melatonin (OM) administration alone and combined with short-wavelength light (SWL)-blocking filters on patients with RP and test their effectiveness in improving the level of stress and sleep problems in many of these patients. We have developed a low-cost therapy protocol for patients with RP with sleep disorders and negative psychological stress. Patients will be randomized to receive a combined intervention with SWL-blocking filters and OM, SWL-blocking filters alone, or OM alone. There will also be a nonintervention arm as a control group. This study will be conducted across 2 retinal units in patients with RP with sleep disorders and high perceived stress and anxiety score reports. Patients will be assessed in the preintervention period, weekly during the 4 weeks of intervention, and then at 6 months postintervention. The primary outcomes are the differences in changes from baseline to postintervention in hormone release (α-amylase, cortisol, and melatonin) and sleep quality, as measured with the visual analog scale. Secondary outcome measures include clinical macular changes, as measured with optical coherence tomography and optical coherence tomography angiography; retinal function, as measured using the visual field and best-corrected visual acuity; sleep data collected from personal wearables; and several patient-reported variables, such as self-recorded sleep diaries, quality of life, perceived stress, and functional status. This project is still a study protocol and has not yet started. Bibliographic research for information for its justification began in 2020, and this working group is currently seeking start-up funding. As soon as we have the necessary means, we will proceed with the registration and organization prior to the preliminary phase. In this feasibility randomized clinical controlled trial, we will compare the effects of SWL blocking alone, administration of OM alone, and a combined intervention with both in patients with RP. We present this study so that it may be replicated and incorporated into future studies at other institutions, as well as applied to additional inherited retinal dystrophies. The goal of presenting this protocol is to aid recent efforts in reducing the impact of sleeping disorders and other psychological disorders on the quality of life in patients with RP and recovering their self-autonomy. In addition, the results of this study will represent a significant step toward developing a novel low-cost therapy for patients with RP and validating a novel therapeutic target. PRR1-10.2196/49196.

Unstable Subsynchronous Interaction Induced by Blocking Filters in a Wind-Thermal Combined Power System

Blocking filters (BFs) are applied to reduce the risk of shaft related subsynchronous resonance (SSR) in thermal power plants connected to series compensated transmission lines. However, when doubly-fed induction generator (DFIG)-based wind farms are connected in parallel with the existing thermal power plants, the same BFs may cause unstable subsynchronous interaction (SSI) with the DFIGs. This paper investigates the potential risk of this new type of SSI caused by BFs, which are originally designed to reduce the SSR risk. First, a representative system model of thermal power units with BFs and DFIGs integrated into grid is established. Then, impedance-based analyses and time-domain simulations are carried out to analyze the mechanism and characteristics of the SSI. The results indicate that the interaction between BFs and DFIGs may induce unstable oscillation in the system. In particular cases where series compensation in the transmission line is bypassed, the risk of SSI instability still exists. With series compensation operating normally, the interaction among BFs, DFIGs, and series compensated lines becomes even more complex. The paper also investigates the effects of system parameters such as the number of online DFIGs, wind speed, and series compensation level on the SSI characteristics.

Enhancement of the structural, optical, and dispersion performance of polyvinyl alcohol via coronene additive for optoelectronic applications

Composite films made of polyvinyl alcohol (PVA) filled with various coronene concentrations were fabricated via the solution casting method. Several characterization techniques were used to examine the prepared samples. The x-ray diffraction study shows decreasing semi-crystalline properties in PVA/coronene composites with increasing coronene levels, thereby improving charge carrier mobility and enhancing conductivity. The alterations in the chemical functional groups of the PVA/coronene composites were explored using Fourier-transform infrared spectroscopy (FTIR). The impact of coronene molecules on the optical characteristics of PVA was investigated in the spectral ranges of 190-2500 nm. PVA/coronene composite exhibits higher UV blocking in the 190-400 nm wavelength range, suitable for UV notch filters like laser blocking filters. By increasing the coronene filling ratio from 0 wt% to 3 wt%, both the indirect and direct optical band-gap of PVA films decreased from 5.19 eV and 5.77 eV to 3.85 eV and 5.18 eV, respectively. The single oscillator model (Wemple-DiDomenico) was used to explain the refractive index dispersion region. The extracted values of dispersion energy (Ed), oscillator energy (Eo), dielectric constant at infinite frequency (ε ∞), and lattice dielectric constant (ε L) of PVA/coronene composite samples increased from 0.78 eV, 2.41 eV, 1.32 and 1.41 to 13.44 eV, 12.22 eV 2.10 and 2.13, respectively. These changes in dispersion parameters are due to cross-linking between the PVA polymeric matrix and the coronene. As a result of these improvements, PVA/coronene films could be applied to flexible packaging applications and optoelectronic devices like solar cells or light-emitting diodes.

Ultracompact Integrated Mode-Order Converter and Reciprocal Optical Diode with Etched Subwavelength Structures

Three ultracompact integrated photonic devices are proposed, assisted by etched structures. A mode-order converter (MOC) is achieved with a footprint of 0.85 × 1.4 μm2, which exhibits high performances with insertion loss (IL) below 0.34 dB and mode purity (MP) above 90% within 100 nm waveband. Moreover, a mode blocking filter (MBF) is proposed based on a subwavelength grating with a footprint of 0.8 × 4.12 μm2, which allows the propagation of TM0 mode but blocks the TM1 mode with a remarkably high extinction ratio of 31.6 dB at the wavelength of 1550 nm. Finally, a compact reciprocal optical diode (ROD) is presented by cascading the abovementioned MOC and MBF with a footprint of 0.85 × 5.9 μm2. This ROD enables one-way transmissions for both TM0 mode and TM1 mode with contrast ratios of 19.74 dB and 32.04 dB, respectively. The design methodology paves a new way for mode manipulation in integrated multimode photonic circuits.

Design and acoustic tests of the ATHENA WFI filter wheel assembly development model towards TRL5

The filter wheel (FW) assembly (FWA), developed by the CBK Institute, is one of the critical subsystems of the wide field imager (WFI) instrument on board the Advanced Telescope for High Energy Astrophysics—mission of the ESA Cosmic Vision 2015-25 space science program (launch scheduled around 2035). The instrument has to collect soft x-rays with very high quantum efficiency, thus WFI requires extremely thin optical blocking filter (OBF). Due to its thickness (∼150 nm) and large area (∼170 mm × 170 mm) needed to achieve a 40 ′ × 40 ′ instrument field of view, the filter is extremely vulnerable to acoustic loads generated during Ariane 6 rocket launch. On the other side, FW mechanism has to provide high overall reliability, so it is more favourable to launch the instrument in atmospheric pressure (without vacuum enclosure for filter protection). Design efforts of the FW subsystem were focused on two issues: providing maximal possible sound pressure level suppression and smallest possible differential pressure across the OBF, which should prevent filters from damaging. We describe the design of a reconfigurable acoustic-demonstrator model (DM) of WFI FWA created for purposes of acoustic testing. Also, the acoustic test campaign is described: test methodology, test criteria, and results discussion and its implication on future FWA design. In general, tests conducted with the FWA DM showed that current design of WFI is feasible and the project can be continued without introducing a vacuum enclosure, which would significantly increase system complexity and mass.

Structural and UV-blocking properties of carboxymethyl cellulose sodium/CuO nanocomposite films

Nanoparticles have made a substantial contribution to the field of skincare products with UV filters in preserving human skin from sun damage. The current study aims to create new polymer nanocomposite filters for the efficient block of UV light that results from the stratospheric ozone layer loss. The casting approach was used to add various mass fractions of copper oxide nanoparticles (CuO-NPs) to a solution of carboxymethyl cellulose (CMC). The amorphous nature of CMC was revealed by XRD analysis, with the intensity of the typical peak of virgin polymer in the nanocomposite spectrum decreasing dramatically as the doping amount was increased. The FTIR spectra revealed the functional groups of CMC and the good interaction between the CMC chain and CuO-NPs. Optical experiments revealed that the optical transmittance of pure CMC was over 80%, whereas it dropped to 1% when CuO-NPs content was increased to 8 wt.%. Surprisingly, the inclusion of CuO-NPs considerably improved the UV blocking property of the films extended from the UV region (both UV-A: 320–400 nm and UV-B: 280–320 nm) to the visible region. Optical band gap of CMC decreased sharply with increasing CuO concentration. The tunable optical characteristics can be utilized in UV- blocking filters and various optoelectronics applications.

A semiconductor Sc2S3 monolayer with ultrahigh carrier mobility for UV blocking filter application.

For humans, ultraviolet (UV) light from sun is harmful to our eyes and eye-related cells. This detrimental fact requires scientists to search for a material that can efficiently absorb UV light while allowing lossless transmission of visible light. Using an unbiased first-principles swarm intelligence structure search, we explored two-dimensional (2D) Sc-S crystals and identified a novel Sc2S3 monolayer with good thermal and dynamical stability. The optoelectronic property simulations revealed that the Sc2S3 monolayer has a wide indirect bandgap (3.05 eV) and possesses an ultrahigh carrier mobility (2.8 × 103 cm2 V-1 s-1). Remarkably, it has almost transparent visible light absorption, while it exhibits an ultrahigh absorption coefficient up to × 105 cm-1 in the ultraviolet region. Via the application of biaxial strain and thickness modulation, the UV light absorption coefficients of Sc2S3 can be further improved. These findings manifest an attractive UV blocking optoelectronic characteristic of the Sc2S3 configuration as a prototypical nanomaterial for the potential application in UV blocking filters.

Design and test results of different aluminum coating layers on the sCMOS sensors for soft X-ray detection

In recent years, tremendous progress has been made on complementary metal-oxide-semiconductor (CMOS) sensors for applications as X-ray detectors. To shield the visible light in X-ray detection, a blocking filter of aluminum is commonly employed. We designed three types of aluminum coating layers, which are deposited directly on the surface of back-illuminated sCMOS sensors during fabrication. A commercial 2k × 2k sCMOS sensor is used to realize these designs. In this work, we report their performance by comparison with that of an uncoated sCMOS sensor. The optical transmissions at 660 nm and 850 nm are measured, and the results show that the optical transmission reaches a level of about 10-9 for the 200 nm aluminum layer and about 10-4 for the 100 nm aluminum layer. Light leakage is found around the four sides of the sensor. The readout noise, fixed-pattern noise and energy resolution of these Al-coated sCMOS sensors do not show significant changes. The dark currents of these Al-coated sCMOS sensors show a noticeable increase compared with that of the uncoated sCMOS sensor at room temperatures, while no significant difference is found when the sCMOS sensors are cooled down to about -15°C. The aluminum coatings show no visible crack after the thermal cycle and aging tests. Based on these results, an aluminum coating of a larger area on larger sCMOS sensors is proposed for future work.

Ultraviolet Fluorescence Photography-Choosing the Correct Filters for Imaging.

Ultraviolet (UV) fluorescence is a valuable tool for the imaging of a wide range of subjects. Like all imaging techniques, the key to success depends on the correct choice of equipment and approach used. In fluorescence photography, a filter is placed in front of the camera lens to block unwanted short-wavelength light from entering the camera, which would compromise the image. However, some filters exhibit fluorescence under UV light and can therefore have the potential to produce a color cast on the image. Filters also vary in how well they block unwanted light. A range of commonly used optical filters was assessed for fluorescence under UV light, and their optical transmission between 250 nm and 800 nm was measured. Finally, a simple method to enable the researcher to determine the fluorescence of the filters that they are using or wish to use for their work is described. The results indicate that the filters tested demonstrated a wide range of fluorescence under UV light and varying degrees of UV blocking. Some filters tested had equivalent or reduced fluorescence compared to Schott KV-418, which is a widely used, but, unfortunately, no longer manufactured UV blocking filter commonly used for fluorescence photography.

Mitigation of background harmonic amplification caused by offshore wind farm long AC cable integration

The high voltage alternating current transmission with submarine cables is the common scheme to integrate offshore wind farms close to the land. Due to the capacitive effect of AC cables, the association of the long AC cables and the onshore grid can cause resonances, which may amplify grid background harmonics. This paper focuses on the mitigation of background harmonic amplification caused by offshore wind farm integration. First, the background harmonic amplification mechanism in the offshore wind farm integration system is analysed qualitatively, and the mitigation approaches are given in principle. Then, taking a practical project as a study case, the harmonic modelling methods of the offshore grid and the onshore grid are elaborated, including the harmonic models of wind turbines, transformers, cables, the high voltage and the extra-high voltage transmission grid, and the low voltage distribution network. According to the established harmonic models, the cause of background harmonic amplification is analysed. On this basis, two mitigation methods of installing the series blocking filter and the shunt filter are compared and the recommended mitigation scheme is proposed. Finally, the feasibility of the proposed scheme is verified by calculation results under different grid operating conditions.

The Shendye-Fleming OBA Index for paper and paperboard

We are proposing a new one-dimensional scale to calculate the effects of optical brightening agents (OBA) on the bluish appearance of paper. This index is separate from brightness and whiteness indices. In the paper industry, one-dimensional scales are widely used for determining optical properties of paper and paperboard. Whiteness, tint, brightness, yellowness, and opacity are the most common optical properties of paper and paperboard. Most of the papers have a blue cast generated by addition of OBA or blue dyes. This blue cast is given because of the human perception that bluer is whiter, up to a certain limit. To quantify this effect, it is necessary to determine how much blue cast paper and paperboard have. As the printing industry follows the ISO 3664 Standard for viewing, which has a D50 light source, this also plays a very important role in showing a blue cast. Color perception is based on light source and light reflected from an object. The ultraviolet (UV) component in D50 interacts with OBA to provide a reflection in the blue region of the visible spectrum. Use of a UV blocking filter results in measurements without the effect of emission in the blue region. This difference is used in determining the OBA effect in the visible range of the paper. This equation is known as the Shendye-Fleming OBA Index.

Optics-Free Chip-Scale Intraoperative Imaging Using NIR-Excited Upconverting Nanoparticles.

We present an optics-free CMOS image sensor that incorporates a novel time-gated dual-photodiode pixel design to allow filter- and lens-less image acquisition of near-infrared-excited (NIR-excited) upconverting nanoparticles. Recent biomedical advances have highlighted the benefits of NIR excitation, but NIR interaction with silicon has remained a challenge, even with high-performance optical blocking filters. Using a secondary diode and a dual-photodiode design, this sensor is able to remove the 100s of mV of NIR background on pixels and bring it down to single-digit mV level, nearing its noise floor of 2.2 mV rms, not achievable with any optical filter. Non-linear effects of background cancellation using the diode pair has been mitigated using an initial one-time pixel-level curve fitting and calibration in a post-processing setting. This imager comprises a highly linear 11 fF metal-oxide-metal (MOM) capacitor and includes integrated angle-selective gratings to reject oblique light and enhance sharpness. Each pixel also includes two distinct correlated double sampling schemes, to remove low frequency flicker noise and systematic offset in the datapath. We demonstrate the performance of this imager using pulsed NIR-excited upconverting nanoparticles on standard United-States-Air-Force (USAF) resolution targets and achieve an SNR of 15 dB, while keeping NIR background below 6 mV. This 36-by-80-pixel array measures only 2.3 mm by 4.8 mm and can be thinned down to 25 µm, allowing it to become surgically compatible with intraoperative instruments and equipment, while remaining optics-free.

Exfoliated and bulk β-gallium oxide electronic and photonic devices

<h2>Abstract</h2> Monoclinic gallium oxide (β-Ga₂O₃) has recently attracted increasing attention due to the availability of high quality, large diameter single crystals from mature melt growth methods and its attractive material properties of wide E_G of 4.6–4.9 eV, good electron mobility (>200 cm²/Vs) and estimated E_c of ~8 MV/cm. Compared to other ultra-wide bandgap materials, the inexpensive substrates lower the manufacturing cost for β-Ga₂O₃ power devices. Applications of deep-UV detectors with solar blindness include inspection of high voltage transmission lines for corona and partial discharges, detection of fires and various defense systems. Si- and GaAs-based UV PDs are not truly solar-blind, as additional, bulky visible-light blocking filters are required. In this short review we discuss the use of bulk and exfoliated β-Ga₂O₃ for these applications and relate this to the basic surface and response of the material to high temperatures, radiation exposure and typical semiconductor processing steps. The material can easily be cleaved along the (100) surface and layers with (100)A surface termination have higher energy than the (100)B termination. The (100)B cleavage plane is the favorable one, observed experimentally.

Instrument assessment and atmospheric phenomena in relation to the night sky brightness time series

Several networks of Sky Quality Meters show long-term trends in measuring the night sky brightness. Causes of this variation could be ageing of the instruments and variations of the sky emission. The data from Ekar Observatory (Italy) are here considered.No significant ageing effect was detected on 9-year-old housing windows. A 9-year-old IR blocking filter shows a variation of its spectral transmittance up to 80%.No trend on the SQM output was found due to only the variation of the spectral distribution of the night sky emission. Together with ageing of the IR blocking filter, it causes a reduction of the SQM output of about 0.01magSQMarcsec-2 per year.Slow trend of the aerosol optical depth suggests the air near the considered site is changing towards less polluted conditions. It reduces scattering of the artificial light and consequently sky glow in the light polluted considered site.