UV Bandpass Filters Research Articles

Strain measurement at up to 3000 °C based on Ultraviolet-Digital Image Correlation

Development in aerospace technology makes it increasingly important to understand the thermal-mechanical behavior of materials subject to high temperature ranging from 2000°C to 3000 °C. In this work, a simple and low-cost Ultraviolet-Digital Image Correlation (UV-DIC) system composed of a CCD camera, a telecentric lens and a single UV bandpass filter was proposed for deformation measurement at up to 3000 °C. Hafnium carbide (HfC) powder was used as the speckle pattern material. To verify the UV-DIC system and the speckle pattern, the coefficient of thermal expansion (CTE) of graphite heated by electric current was measured from 25 °C to 3000 °C. The results show that the system can effectively suppress strong heat radiation at up to 3000 °C, and that the prepared speckle pattern can withstand 3000 °C. Comparison of the measured CTE of graphite with that in the existing database verifies the feasibility and accuracy of the proposed method. The proposed method and technology lay the foundation for further development of the DIC in ultra-high temperature deformation measurement.

Self-powered solar-blind α-Ga2O3 thin-film UV-C photodiode grown by halide vapor-phase epitaxy

A compact self-powered solar-blind UV-C photodiode was demonstrated using an ultra-wide bandgap (UWBG) α-Ga2O3 thin film as a wavelength-selective absorber layer. The UWBG-based Schottky junction architecture renders the use of low-performance and bulky solar-blind UV bandpass filters unnecessary. High-quality α-Ga2O3 thin films with a thickness of 1.25 µm were grown on a (0001) sapphire substrate via the halide vapor-phase epitaxy technique. The self-powered solar-blind UV-C photodetector based on the Ni/α-Ga2O3 Schottky junction exhibited excellent responsivity (1.17 × 10−4 A/W), photo-to-dark current ratio (1.12 × 105), and reproducibility, as well as fast rise/decay characteristics without persistent photoconductivity upon exposure to UV-C radiation (254 nm wavelength). The relationship between light intensity (I) and photocurrent (P) was modeled by I ∼ P0.69, indicating the high-quality of the halide vapor-phase epitaxy-grown α-Ga2O3 thin film. Upon exposure to natural sunlight, the fabricated solar-blind photodetector showed excellent solar blindness with sensitivity to UV-C radiation and did not require an external power source. Therefore, this UWBG α-Ga2O3 thin-film Schottky barrier photodiode is expected to facilitate the development of a compact and energy-independent next-generation UV-C photodetector with solar blindness.

An Investigation of the Thermal and Dielectric Properties of Nickel Sulfate Hexahydrate Single Crystal for Sensors, Bandpass Filters and Optical Applications

In the present work, a good-quality nickel sulfate hexahydrate (NSH) single crystal measuring 30 × 20 × 15 mm3 was grown via a slow evaporation solution technique (SEST). NSH single crystal is an inorganic material and is widely used in optical applications, UV sensors, and missile detection systems, among others. The grown crystal was characterized using powder x-ray diffraction (PXRD), UV-visible spectroscopy, microhardness test and etching analysis. Photoacoustic spectroscopy (PAS) was used to identify the thermal diffusivity of the grown crystal. The thermal diffusivity of the NSH crystal was found to be superior to that of various common nonlinear optical (NLO) materials, and is thus suitable for use in optical and sensor applications. Differential scanning calorimetry (DSC) was utilized to determine the material decomposition at a certain temperature. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were performed to identify the melting point of the grown crystal. The dielectric analysis showed that the crystal has low dielectric loss, fewer defects, and better optical properties, and is suitable for NLO applications. Thermal analysis showed that the grown crystal can be utilized for a wide array of applications including optical communications, UV bandpass filters, UV sensors, harmonic generation, and missile detection systems.

National Institute of Standards and Technology transportable tunable ultraviolet laser irradiance facility for water pathogen inactivation.

A method of ultraviolet germicidal irradiation (UVGI) for water pathogen inactivation effectiveness using tunable, narrowband laser light is described. A transportable tunable UV (TTUV) laser system for providing a known irradiance (μW/cm2) or dose (mJ/cm2) suitable for irradiating water samples in Petri dishes over the wavelength range of 210 nm-300 nm was developed by the National Institute of Standards and Technology. The TTUV facility, consisting of a 1 kHz pulsed UV laser and light-tight enclosure containing the optics necessary to uniformly irradiate a water sample, was used in a microbiology laboratory to dose drinking water pathogens and surrogates as part of a Water Research Foundation study in the summer and fall of 2012. The approach demonstrated improved accuracy and simplified spectral analysis over conventional pathogen inactivation sources consisting of broadband UV sources and bandpass filters. In this work, the TTUV facility design and key components are described, including modifications in the field to provide the required irradiance levels. The irradiance and dose levels produced by the tunable UV laser during the project are also presented. The transportability of the TTUV system enabled it to be brought to a microbiology facility allowing the water samples (microbial suspensions) to be irradiated in a location with experienced staff and facilities for preparing, handling, analyzing, storing, and shipping the many samples studied. These results, published elsewhere, established that the tunable UV laser system provides unique UVGI capabilities for use with water pathogens and has applications for other pathogen experiments, for example, air-purification studies.

Modelling of SiPM Performance for Detection of Cherenkov Radiation from Extensive Air Showers in UV and Visible Ranges for Application at the TAIGA-IACT Telescope

Abstract A novel cluster of sensitive detectors based on silicon photomultipliers (SiPM) is being developed for the Cherenkov gamma-ray telescope TAIGA-IACT (Tunka valley, Republic of Buryatia, Russia). The cluster will be able to detect Cherenkov radiation from extensive air showers in two wide bands: 250–300 nm (UV) and 250–700 nm (visible and UV). Each pixel consists of a Winston cone, 4 SiPMs with the total sensitive area of 144 mm2, and readout electronics based on fast analogue memory. During operation in the UV band, a UV-bandpass filter is used to suppress cluster sensitivity in the visible range. In order to evaluate the detection efficiency of the selected SiPMs, a specific software simulator of SiPM output signal has been developed. This simulator takes into account such inherent parameters of SiPMs as total number of microcells, their recharge time, the dark count rate, the effective detection area, the quantum efficiency, the crosstalk between microcells, as well as conditions of SiPM operation, namely, the background noise and the Ohmic load in the readout (front-end) electronics. With this simulator it is possible to determine the expected trigger threshold under given conditions and parameters of selected detectors. Based on preliminary simulations, OnSemi MicroFJ-60035 SiPM chips have been chosen for the novel cluster of TAIGA-IACT. These SiPMs have sensible efficiency in the ultraviolet range (5–20% in the 250–300 nm band) and are distinguished by the presence of a fast output, which allows one to capture a low amplitude signal above a relatively high background noise.

Ultraviolet 3D digital image correlation applied for deformation measurement in thermal testing with infrared quartz lamps

In thermal-structural testing of hypersonic materials and structures, deformation measurement on the front surface of an object directly heated by quartz lamps is highly necessary and very challenging. This work describes a novel front-surface high-temperature deformation measurement technique, which adopts ultraviolet 3D digital image correlation (UV 3D-DIC) to observe and measure the high-temperature deformation fields on front surfaces directly heated by quartz lamps. Compared with existing blue light DIC techniques, the established UV 3D-DIC, which combines UV CCD camera, active UV illumination and bandpass filter imaging, can effectively suppress the strong disturbing light emitted by the quartz lamps and the heated sample itself during heating process. Two experiments were carried out to verify the robustness and accuracy of the developed technique: (1) direct observation of front surfaces of a hypersonic thermal structure sample heated from room temperature to 1050 °C, and (2) front-surface thermal stain and coefficient of thermal expansion (CTE) measurement of an Inconel 718 sample up to 800 °C. The well matched strain and CTE results with literature data show that UV 3D-DIC system is an effective technique for front-surface deformation measurement and has great potential in characterizing deformation response of hypersonic materials and structures subjected to transient aerodynamic heating.

An investigation on optical, mechanical and thermal properties of nickel sulphate hexahydrate single crystal—a UV band pass filter

Nickel sulphate hexahydrate (NSH) crystal is known to be an excellent material for UV light band-pass filter applications. In this research work, good quality and enhanced size of NSH single crystal has been effectively grown by implementing Sankaranarayanan—Ramasamy (SR) method. After a prolonged period of 185 days, a fine quality of transparent as well as improved size single crystal of NSH with dimension 220 mm in length and 12 mm in diameter has been successfully harvested. The grown crystal has been subjected to various characterizations as that of single crystal x-ray analysis to confirm the crystal system with unit cell parameters, UV–Vis analysis to know the transmission spectrum, FTIR spectral analysis to find out the functional groups and photoluminescence study to affirm the green emission of the crystal. NSH crystal falls into the category of soft material as identified by microhardness study and etching study confirms that it has good quality as the surfaces are almost free of defects. Photoacoustic spectroscopy has been utilized to find the thermophysical parameters. The resultant value of thermal diffusivity is compared with few other familiar nonlinear optical materials such that it is asserted by the observed superior value of NSH single crystal that it is an added advantage for band-pass filter and harmonic generation applications.

Highly selective ultraviolet aluminum plasmonic filters on silicon

We report the use of aluminum patterning to make highly selective UV bandpass filters. We design and fabricate a periodic array of nanoholes in Al thin film on a bare silicon substrate as an analog for potential integration with a Si photodetector. Arrays were designed to operate in the wavelength range of 200-400 nm. Our results show that we can obtain a single dominant peak filter with a linewidth of 30 nm at normal incidence, in contrast to similar structures on glass substrates, where multiple modes influence the UV spectrum. Varying the angle of incidence is shown to split the plasmonic mode and further decrease the linewidth of the maximum wavelength mode down to 10 nm. Our results therefore show high potential for applications in solid-state image sensors for astronomy and planetary studies.

Design and manufacture of super-multilayer optical filters based on PARMS technology

Abstract Three multilayer interference optical filters, including a UV band-pass, a VIS dual-band-pass and a notch filter, were designed by using Ta2O5, Nb2O5, Al2O3 and SiO2 as high- and low-index materials. During the design of the coating process, a hybrid optical monitoring and RATE-controlled layer thickness control scheme was adopted. The coating process was simulated by using the optical monitoring system (OMS) Simulator, and the simulation result indicated that the layer thickness can be controlled within an error of less than ±0.1%. The three filters were manufactured on a plasma-assisted reactive magnetic sputtering (PARMS) coating machine. The measurements indicate that for the UV band-pass filter, the peak transmittance is higher than 95% and the blocking density is better than OD6 in the 300–1100 nm region, whereas for the dual-band-pass filter, the center wavelength positioning accuracy of the two passbands are less than ±2 nm, the peak transmittance is higher than 95% and blocking density is better than OD6 in the 300–950 nm region. Finally, for the notch filter, the minimum transmittance rates are >90% and >94% in the visible and near infrared, respectively, and the blocking density is better than OD5.5 at 808 nm.

Growth of K2Ni(SO4)2·6H2O crystal by Sankaranarayanan–Ramsamy (SR) method for UV light band-pass filter

A [011] direction potassium nickel sulphate hexahydrate (KNSH) crystal was grown from an aqueous solution by uniaxially solution-crystallization method of Sankaranarayanan–Ramsamy (SR). The grown crystal was examined by X-ray diffraction, UV–Vis–NIR spectroscopy and TGA analysis methods. Optical transmission spectrum of the grown crystal revealed its suitability for use as UV band pass filter.

Monomeric Rhodopsin Is Sufficient for Normal Rhodopsin Kinase (GRK1) Phosphorylation and Arrestin-1 Binding

G-protein-coupled receptor (GPCR) oligomerization has been observed in a wide variety of experimental contexts, but the functional significance of this phenomenon at different stages of the life cycle of class A GPCRs remains to be elucidated. Rhodopsin (Rh), a prototypical class A GPCR of visual transduction, is also capable of forming dimers and higher order oligomers. The recent demonstration that Rh monomer is sufficient to activate its cognate G protein, transducin, prompted us to test whether the same monomeric state is sufficient for rhodopsin phosphorylation and arrestin-1 binding. Here we show that monomeric active rhodopsin is phosphorylated by rhodopsin kinase (GRK1) as efficiently as rhodopsin in the native disc membrane. Monomeric phosphorylated light-activated Rh (P-Rh*) in nanodiscs binds arrestin-1 essentially as well as P-Rh* in native disc membranes. We also measured the affinity of arrestin-1 for P-Rh* in nanodiscs using a fluorescence-based assay and found that arrestin-1 interacts with monomeric P-Rh* with low nanomolar affinity and 1:1 stoichiometry, as previously determined in native disc membranes. Thus, similar to transducin activation, rhodopsin phosphorylation by GRK1 and high affinity arrestin-1 binding only requires a rhodopsin monomer.

The Minimal Instrumentation Requirements for Hoechst Side Population Analysis: Stem Cell Analysis on Low‐Cost Flow Cytometry Platforms

The Hoechst side population (SP) technique is a critical method of identifying stem cells and early progenitors in rodent, nonhuman primate, and human hematopoietic and nonhematopoietic tissues. In this technique, the cell-permeable DNA-binding dye Hoechst 33342 is loaded into the cell population of interest; stem cells and early progenitors subsequently pump this dye out via an ATP-binding cassette membrane pump-dependent mechanism, resulting in a low-fluorescence "tail" (the SP) when the cells are analyzed by flow cytometry. This population contains stem cells and early progenitors. One significant drawback of this method is the requirement of an UV laser to excite the Hoechst 33342. Unfortunately, flow cytometers equipped with UV sources are expensive to own and operate and are not readily available to many laboratories or institutions. In the interests of designing a less expensive flow cytometric system for stem cell analysis, we determined the minimum UV excitation and instrumentation requirements for measuring Hoechst SP. Less than 3 mW of UV laser output was required for adequate resolution of Hoechst SP on two cuvette-based flow cytometers, one of which was a simple, inexpensive benchtop analyzer (the Quanta Analyzer; NPE Systems). Furthermore, Hoechst SP could also be adequately resolved on this epifluorescence-based cytometer platform using two nonlaser UV sources, a mercury arc lamp with a UV bandpass filter and a UV-emitting light-emitting diode. These results suggest that an economical flow cytometric system can be designed that is capable of resolving Hoechst SP, with a cost far lower than most UV laser-equipped commercial systems. An inexpensive system of this type would make Hoechst SP analysis available to a much broader group of stem cell investigators.

Detection of fast pulses from large barium fluoride calorimeters

Two components of the scintillation emitted from large barium fluoride (BaF2) crystals were quantitatively measured with UV photomultipliers. To suppress the slow component, thereby detecting the fast one selectively, CsTe UV photomultipliers and bandpass filters were applied. By using both devices we obtained α = 4.1, where α is defined as the fast-to-slow component ratio of the light yield. The capability of electron/pion separation can be improved by employing information concerning α, in addition to the ordinary cut in the total energy deposit, by an additional factor of 4.5 (at 300 MeV/c) to 1.6 (1000 MeV/c). We obtained a pion rejection factor of 1100 to 17000 at 300–1000 MeV/c in a 17.5 cm long BaF2 calorimeter. We also observed the difference between the response to protons and that to electrons or pions in the momentum range from 500 to 1000 MeV/c.

Ultraviolet Light from the Nighttime Sky Enhances Retinal Sensitivity of Limulus.

Here we report that stimulation of the median ocelli of the horseshoe crab, Limulus polyphemus, by UV light from the nighttime sky enhances the sensitivity of the lateral eyes to visible light. At night a circadian clock in the brain of Limulus generates and transmits neural activity via efferent optic nerve fibers to the lateral eyes and median ocelli (8), significantly increasing their sensitivity (9,lO). Experiments carried out in the laboratory show that illumination of the median ocelli at night with UV light enhances the clock’s efferent output and thus further increases the sensitivity of the lateral eyes and median ocelli (11). We tested whether this occurs under natural conditions; that is, whether ocellar exposure to UV light from the nighttime sky increases visual sensitivity of the lateral eyes. We carried out our experiments in an outdoor shed located in a remote area of Woods Hole, MA, where no artificial light was detectable at night. We mounted animals securely to a platform in an aquarium so that their gills were irrigated with recirculated seawater, but their lateral eyes and median ocelli remained above water. An opaque chamber was placed over the right lateral eye of each animal to occlude the eye from ambient light. A wick electrode and light emitting diode (LED) within the chamber allowed us to record electroretinograms (ERGS) from the eye in its dark-adapted state while the animal was exposed to normal diurnal changes in illumination. A computerbased system recorded ERGS every 30 min in response to a 10 ms light flash from the LED (12). Changes in the amplitude of the ERG of the occluded right eye provided a measure of the clock’s effect on retinal sensitivity and the ocellar influence on the clock’s action. Animals (n = 7) were maintained in this apparatus for approximately one month. During this period, ERGS were monitored while the median ocelli were either fully exposed, covered by a UV blocking filter (blocks y < 420 nm), a UV bandpass filter (ymaX = 360 nm, 54 nm bandwidth at half maximum) or occluded to block all incident light. Figure 1 shows the ERG data recorded from the lateral eye of an animal during five days of a month-long experiment (1990). The amplitude of the ERG increased at night and decreased during the day. The extent of the change depended, in part, on the light incident on the median ocelli. Fully exposing the ocelli to the nighttime sky on 19

Radiant Power Flow and Absorptance in Thin Films

Equations are developed for the flow of radiant power, transmittance, and absorptance of an absorbing multilayer, in terms of its characteristic matrix and the admittance of the surrounding media. This is applied to the design of bandpass filters and absorbing coatings. Some uv bandpass filters which contain several aluminum films are designed.