Degradation Of Transmittance Research Articles

Optical transmittance degradation in tapered fibers

We investigated the cause of optical transmittance degradation in tapered fibers. Degradation commences immediately after fabrication and it eventually reduces the transmittance to almost zero. It is a major problem that limits applications of tapered fibers. We systematically investigated the effect of the dust-particle density and the humidity on the degradation dynamics. The results clearly show that the degradation is mostly due to dust particles and that it is not related to the humidity. In a dust free environment it is possible to preserve the transmittance with a degradation of less than the noise (±0.02) over 1 week.

Effects of hydrogen plasma treatment on the structural and electrical properties of sputter-deposited SnO2 thin films

In this paper, we report the effects of hydrogen plasma treatment on the structural and electrical properties of SnO2 thin films prepared by the sputtering method. Whereas the hydrogen plasma treatment led to etching of SnO2 films and subsequent degradation of crystalline quality and optical transmittance, the plasma-treated films exhibited an improvement in the electrical conductivity. Hall measurements indicated an increase in the carrier concentration of SnO2 films which, following x-ray diffraction and secondary ion mass spectrometry measurements, was attributed to the generation of oxygen vacancies rather than the incorporation of hydrogen shallow donors in undoped SnO2 films.

Study on the Effect of Fe<sub>3</sub>O<sub>4</sub> Nanoparticle Dopants on the Properties of Magneto Optical Glasses

Fe3O4 nanoparticles doped magnetic-optical PbO-Bi2O3-B2O3 glasses were prepared and studied and the effects of Fe3O4 nanoparticle on the properties of magnetic-optical glass were analyzed. It is found that the doping of Fe3O4 nanoparticles into glasses increased the Verdet constant of magneto optical glass without evident degradation in glass transmittance. The formation of Fe3O4 nanoparticles was obtained through coprecipitation of Fe(II) and Fe(III) in alkaline media. The structure and properties of doped glasses were studied by X-ray diffraction (XRD), scanning electric microscope (SEM), UV-VIS spectray analysis and Faraday rotation test etc.

The electrical and optical properties of direct-patternable SnO2 thin films containing Pt nanoparticles at various annealing temperatures

The optical and electrical characteristics of SnO2 films with 0.02at.% Pt nanoparticles were studied after annealing at various temperatures. Pt nanoparticles were synthesized by a methanol reduction method and their size was limited to 3nm on average using PVP [poly(N-vinyl-2-pyrrolidone)] as a protecting agent. The electrical conduction of the SnO2 films was enhanced by the introduction of Pt nanoparticles without degradation of optical transmittance. The resistivity and transmittance of the SnO2 films with and without Pt nanoparticles after annealing at 700°C were 2.9×10−2Ωcm and 86.45%, and 1.5×10−1Ωcm and 85.75%, respectively. The observed enhancement in electrical properties was attributed to an increase in carrier concentration due to the addition of Pt nanoparticles. The fact that almost no change in transmittance was observed is explained by the small quantities produced and small particle sizes of the Pt nanoparticles. Well-defined 30-μm-wide direct-patterned SnO2 films containing Pt nanoparticles were formed by photochemical metal-organic deposition using a simple process including a photosensitive starting precursor, UV exposure, and removal of the un-patterned area with solvent rinsing.

Study of Space Microimpacts on Solar Cells and Evaluation of Resultant Degradation

Space microdebris effects were simulated on a newly developed coaxial plasma accelerator; characteristics of damage morphologies on cover glass and the damage equation, which describes the dependence of damage morphology dimension on the impact parameters, were obtained. Themethods to evaluate surface damage ratio and transmittance degradation of solar cells were investigated and applied to a typical sun synchronous spacecraft. For a lifetime of 10 years, the surface damage ratio of solar cell is 0.61 percent on average and amounts to 2.3 percent in the worst case. The averaged andmost severe possible transmittance degradations are 0.5 and 1.5 percent, respectively.

UV degradation of the optical properties of acrylic for neutrino and dark matter experiments

UV-transmitting (UVT) acrylic is a commonly used light-propagating material in neutrino and dark matter detectors as it has low intrinsic radioactivity and exhibits low absorption in the detectors' light producing regions, from 350 nm to 500 nm. Degradation of optical transmittance in this region lowers light yields in the detector, which can affect energy reconstruction, resolution, and experimental sensitivities. We examine transmittance loss as a result of short- and long-term UV exposure for a variety of UVT acrylic samples from a number of acrylic manufacturers. Significant degradation peaking at 343 nm was observed in some UVT acrylics with as little as three hours of direct sunlight, while others exhibited softer degradation peaking at 310 nm over many days of exposure to sunlight. Based on their measured degradation results, safe time limits for indoor and outdoor UV exposure of UVT acrylic are formulated.

水分子吸着による人工衛星光学硝材の透過率変動計測

Gas adsorption onto optical surfaces equipped in satellites is one of the causes of signal degradation occurred in orbit and water is one of the most potent ad-molecules. To estimate the degradation caused by water adsorption onto optical glass surface, the transmittance measurements were carried out in UV-VIS (200--800nm) and IR (1.7--20μm) wavelength ranges. Five kinds of glasses, SiO2, BK7, Al2O3, CaF2, and ZnSe, which are typically used for satellite optics, were selected as glass samples. In IR wavelength range, a local absorption feature was appeared at λ=3.1μm when a glass temperature was below 200K. The phase change of adsorbed water from vapor to solid may account for the newly appeared absorption. In UV-VIS region, there was no local absorption feature but broad transmittance decrease. BK7 and ZnSe, which are hydrophobic, showed little transmittance decrease and it was hard to find the wavelength dependence for their transmittance spectra. On the other hand, the transmittance spectra of hydrophilic glasses, SiO2, Al2O3, and CaF2, showed wavelength dependence and had the local minimal value. From our computation, it is found that the growth of ice grains on a glass surface makes it possible to reproduct the spectral transmittance degradation detected for hydrophilic glasses.

Recovery of fused silica surface damage resistance by ion beam etching

An increase of photoluminescence induced by laser irradiation in vacuum was observed for the fused silica. The degradation of transmittance and damage resistance performance of fused silica surfaces may be due to substoichiometric silica and a sufficient defect population introduced in the near surface. When the laser-irradiated surface layers were removed by ion beam etching, the laser-induced damage threshold recovered to that of un-irradiated samples. The photoluminescence also decreased after ion beam etching. According to the calculated etching depth, the laser-induced defects formed in the surface layer of 10–20 nm when different parameters used during vacuum exposure. In addition, the evolution of surface root-mean-square microroughness as a function of ion beam etching time was studied by the optical interferometric technique and atomic force microscopy.

Impact of rain on radar transmittance through building walls

We study and exactly evaluate the transmittance of microwave energy—below S-band—that goes through thick building walls covered by an external thin layer of rain. The incident radiation penetrates the wet walls at normal incidence, twice in their back-and-forth paths typical of sensing-through-the-wall (STTW) operations. The walls are responsible for most of the loss through the structure in view of their greater thickness, but the water layer contribution is significant, and it is quantitatively evaluated here. The properties of the water layer are expressed in terms of Debye's classical formulation, and those of the walls are obtained from available measurements. A simple homogenization technique is used to generate an “effective permittivity” of the double layer to be able to alternatively treat it as a single equivalent layer—an approximation to the exact values, which yields acceptable results. It is also found that the transmittance T and the reflectance R of a single and double layer could also be expressed in alternative and apparently novel forms that may simplify future calculations. Further, if either R or T were known as well as the layer(s) properties, then either one could be used to obtain the other. Finally, representative plots are displayed, quantitatively showing the (two-way) transmittance degradation that occurs when there is a rain layer on top of the various considered wall materials, and we explain a resonance effect observable in the transmittance plots that shows an oscillatory frequency behavior.

Lens-cementing technology used in optical systems of deep-ultroviolet wavelength regions

In this work, a newly developed optical lens cementing technology is reported. A fluoride material is used as an optical cement that can reduce damage from deep-ultraviolet (DUV) radiation. The degradation of transmittance and the surface quality of the cemented optical elements, including adhesive used for cementing, are evaluated after prolonged DUV irradiation. It is shown that with a 248-nm wavelength, this cement works quite well, up to 1000 h of operation, and the change in transmittance is negligible where average irradiation power is within 27 to 37 mW/cm2. Hence for all practical purposes, the use of this cement in microscope objectives is quite acceptable for 248-nm applications, thus confirming that this cementing technology is satisfactory and meets the performance requirement of DUV inspection systems.

Optical and photocatalytic properties of TiO2 with hollow nanostructure

The effect of hollow nanostructure of TiO2 on the degradation of organic compounds and optical transmittance in the visible-light range was investigated. TiO2 hollow nanoparticles (HNP) consisting of a mixed phase of anatase and rutile in the ratio of 6:4, had a mean size of 70 nm and shell thickness of 5–7 nm. Spectrophotometry study showed that the transmittance of hollow particles was less than 30% in the wavelength range of 320–800 nm. Also, degradation experiment revealed hollow particles exhibited relatively poorer degradation compared to that of commercial P25 powder. These results indicate that movement of electron and light propagation can be affected by the hollow nanostructure.

Postfluorination of fluoride films for vacuum-ultraviolet lithography to improve their optical properties

Transmittance of fluoride films prepared by various kinds of deposition methods is not sufficient for a vacuum-ultraviolet (VUV) stepper application. Moreover, moisture penetrates into fluoride films because of porous structures. Then the moisture reacts with the fluoride chemically, and the photoabsorption of the films increases with elapsed time. Postfluorination treatment, in which F-poor areas of fluoride films are sufficiently fluorinated and the film structures are modified to be denser, has been developed. The postfluorination treatment was performed at 0.1 MPa of diluted F2 gas in a special apparatus made of nickel. This treatment reduces photoabsorption of fluoride films and prevents photoabsorption from increasing again with elapsed time. In a long-time F2 laser irradiation test, the transmittance of as-deposited fluoride films remarkably degraded with irradiation. On the other hand, there is no tendency of transmittance degradation in the case of postfluorinated fluoride films. The postfluorination is able to improve the optical performance of fluoride films, promising the highest coating level for VUV lithography.

原子状酸素と紫外線の複合照射による透明フィルムの光学特性変化

ETFE film covered solar array was developed for arc mitigation in LEO environment. We used ETFE film because its transmittance is excellent at the wavelengths from 300 to 900nm. In LEO, however, the film will encounter serious space environment, such as AO and UV. Electrical power output may decrease due to degradation of transmittance. To study the effects of AO and UV radiation on ETFE film, we used a combined space effect test facility at JAXA. Although the film color turned white after the test, there was no change of film transmittance. Because of AO-induced erosion, texture structure was formed on the film surface, that trapped incident light and made it pass the film after scattering.

Oriented growth of large size calcium fluoride single crystals for optical lithography

We report (1 1 1), (1 1 0) and (1 0 0) growth of CaF 2 by the vertical Bridgman method. Crystals up to 250 mm diameter were grown and various growth parameters such as growth rate, temperature gradient and post-growth cooling rate were studied. It was found that the growth rate and the cooling rate are slower for the larger diameter crystals with a fixed temperature gradient. These growth parameters were optimized for growing the crystals along specific orientation after realizing that CaF 2 has a tendency to grow along an orientation close to 〈1 1 0〉. Degradation in optical transmittance was evaluated by irradiating the crystal to γ -rays up to a dose of 10 5 rad. Optimized scavenger addition resulted in crystals with better radiation resistance and excellent VUV transmittance.

On the Polymer Thickener for Viscosity-Stabilized Solar Pond

The optimal physical properties of an ionized polyacrylamide solution, selected as the most suitable thickener for the insulating layer of a viscosity-stabilized solar pond, are described. Light transmittance, viscosity and viscosity degradation were obtained for a range of thicknesses from 1 cm to 15 cm (1–15 cm), weight concentrations of 0.1–0.5% (0.1–0.5 wt%) and temperatures of the polymer of 20–80°C. Onset of co nvection was also measured for a given thickness of the polymer solution. An exposure test was carried out to prevent degradation of the polymer using an antioxidant. It was confirmed that the viscosity was not decreased and, on the contrary, increased slightly after 100 days. It was shown experimentally that the critical Rayleigh number coincided with the theoretical values reported by Tien et al.. [Int. J. Heat Mass Transf. 12 (1969) 1173]. Transmittances of the polymeric gel for the case of vessels greater than 5 cm in thicknesses were better than those of the SPR402 solution (0.5 wt%).

Highly textured and conductive undoped ZnO film using hydrogen post-treatment

We proposed a method to enhance the characteristics of undoped ZnO films by H2 post-treatment using photochemical vapor deposition. The resistivity of a H2-treated film decreased from 1×10−2 to 2×10−3 Ω cm, the haze ratio increased from 37% to 48%, and no degradation of total transmittance was observed. There are two possible explanations for these phenomena. First, hydrogen atoms assist the desorption of oxygen atoms from the film, resulting in decreased resistivity. Second, hydrogen atoms etch small grains growing among large ones on the surface of the film, resulting in a rough surface.

Cadmium tungstate scintillators with excellent radiation hardness and low background

Small single crystals of CdWO 4 were irradiated by 60Co γ-rays for accumulated doses in the range of 10 4 to 10 8 rad. Degradation in optical transmittance was less than 2%/cm for doses up to 10 8 rad when the measurement was carried out a few to several tens of hours after irradiation. The result is discussed in comparison with the larger damage reported previously. The intrinsic background spectrum indicates that there are much less radioactive impurities in CdWO 4 than in GSO:Ce and BGO.

Radiation damage of a cerium-doped lutetium oxyorthosilicate single crystal

Degradation in optical transmittance due to irradiation with 60Co γ-rays is less than 1% per cm below 10 6 rad, about 2.5% at 10 7 rad, and 7% at 10 8 rad. Spontaneous recovery occurred only partially with a time constant of the order of days to tens of days. Neither recovery nor damage was sizable upon exposure to UV light. Almost full recovery occurred by thermal annealing at 300°C for one day.

Scintillation characteristics of PbWO 4 single crystals at room temperature

Single crystals of PbWO 4 at room temperature show a narrow excitation peak around 325 nm with the FWHM as small as 10 nm and a broad emission peak around 420–440 nm. The light output is about 4.4% of that in BGO. The luminescence is fast with the decay constant less than 10 ns for 84% and as fast as 40 ns for the rest. Degradation in optical transmittance due to γ-ray irradiation is not large up to at least 10 7 rad in the present crystals which are slightly coloured yellow. Spontaneous recovery of the radiation damage occurs to some extent with a time constant much shorter than 18 days. The above result indicates a possibility that this material may be resistive enough against radiation if colourless crystals could be grown.

Radiation damage of BGO crystals due to low energy γ rays, high energy protons and fast neutrons

Results are presented on the effects of radiation on BGO crystals. It is shown that BGO has more than two orders of magnitude higher resistance against low energy γ rays than SF5 lead glass. Darkening of the crystal is hardly visible even after an irradiation of 3.6 × 10 6 R. The darkening faded by more than one half after several days and it has almost completely disappeared after much longer periods. The tolerable rate of synchrotron radiation on BGO calorimeters is 100 R/h in a conservative estimate if the degradation in transmittance is required to be less than 1 % over a depth of 20 radiation lengths. In BGO calorimeters, the degradation of scintillation efficiency is less important than that of the transmittance, 99.999% pure crystals have a two orders of magnitude better resistance than 99.99% pure ones. Sample darkening caused by 12 GeV protons or fast neutrons is an order of magnitude more severe than that by low energy γ rays. Moreover, the recovery is not complete even after a period of more than 100 days. Some data on sample activation are also presented.