Spectral Transmittance Measurements Research Articles

A study of thickness dependence on omnidirectional anti-reflection SiO2 nanorod array fabricated by oblique angle deposition

In this paper, we experimentally demonstrated the oblique angle deposition silicon dioxide nanorods as good anti-reflection coating materials. The nanostructures morphologies and the optical properties were characterized by field-emission scanning electron microscopy and transmission electron microscopy. The influence of the OAD on the optical property of the SiO2 dense and SiO2 nanorods film were investigated by the spectral transmission measurement in 200-1200 nm wavelength regimes. The angle-dependent transmission from 0° to 45° incident angles results demonstrate that increased transmittance through the SiO2 nanosrods surface compared to that of the SiO2 films coated glass. The SiO2 nanorods with 800 nm-thick have transmission closed to the SiO2 film and glass substrate. In addition, the high transmission was observed for angles of incidence up to 45°. The SiO2 nanorods array makes this omnidirectional antireflection concept easily applicable to a wide range of devices.

Soil Temperature in Greenhouse Soil Solarization Using TIF and VIF as Mulching Films

Abstract. The aim of this study was to evaluate the performance of totally impermeable film (TIF) and virtually impermeable film (VIF), generally used in fumigation, in increasing soil temperature during greenhouse solarization treatment in comparison with a commonly used LDPE film. Preliminary laboratory measurements of the perpendicular spectral transmittance of these film were performed in solar (200-2500 nm) and infrared (2500-25,000 nm) wavelength ranges. Subsequently, a field trial was carried out in Sicily in a multi-span tunnel greenhouse, with a steel structure, covering a 90.0 m × 24.0 m surface of sandy soil. Four treatments were performed on 3 m × 24 m plots arranged in a randomized complete block design (RCBD) with three replications. For each replication, one plot was left unmulched as control, and three plots were mulched with TIF, VIF, or LDPE film. The solarization treatments were performed from 17 July to 6 September 2015. During all trials, soil temperature was measured at 5, 15, and 30 cm depths. Air temperature, air relative humidity, and total radiation flux were measured outside and inside the greenhouse. The results show that TIF and VIF both have better spectroradiometric properties than LDPE film and that the soil temperatures at 15 and 30 cm depths under TIF and VIF were significantly higher than the temperatures under LDPE film. These results encourage the use of low-dosage fumigation followed by solarization for control of soil pathogens to obtain further reduction in the amount of fumigant used. Keywords: Greenhouses, Soil solarization, Totally impermeable film (TIF), Virtually impermeable film (VIF).

Report on the bilateral comparison between BIM (Bulgaria) and VSL (The Netherlands)

A bilateral comparison has been organized between VSL, The Netherlands and BIM, Bulgaria in the field of spectral regular transmittance measurements. This comparison is registered as EURAMET project nr. 1073 and EURAMET.PR-K6.2 in the BIPM key comparison database.The aim of the comparison is to demonstrate the improvement of calibration measurement capabilities of BIM in this working field. If this comparison is successful, i.e. the results support the claimed improvement in uncertainties, the improved CMC's for BIM will be included in Appendix C of the CIPM mutual recognition arrangement (MRA).The results of this comparison are linked to key comparison CCPR K6.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Determination of the optical constants of a dielectric layer by processing in situ spectral transmittance measurements along the time dimension.

This paper describes a new method based on the use of a broadband monitoring system to determine the spectral dependence of the optical constants of a layer without using a dispersion model.

Application of indium zinc oxide window layers in Cu(In,Ga)Se2 solar cells

Recently, indium-based transparent conductive oxides have become more interesting for application in Cu(In,Ga)Se2 (CIGS) solar cells. Although the fabrication costs may be higher than for standard ZnO:Al (AZO), amorphous indium zinc oxide (IZO) films are very attractive due to their high charge carrier mobilities leading to high conductivity. Additional advantages are that the substrate does not need to be heated during sputter coating and that the films demonstrate superior stability against humidity.We investigate the deposition of IZO films by RF and DC magnetron sputtering in dependence of sputtering power, total pressure, oxygen and hydrogen admixture, and substrate temperature. The IZO films on glass are analysed by means of conductivity, spectral transmittance, and Hall measurements as well as X-ray diffraction and scanning electron microscopy. Specific resistivity below 350μΩcm is obtained for 0.4μm thick films, half that of AZO. Best mobilities of about 50cm2/Vs are achieved for highly transparent films.The suitability of IZO as a window layer for CIGS solar cells is demonstrated with efficiencies as high as 19.5% comparable to the AZO reference. Results for stability tests of IZO-coated CIGS modules in damp heat will be discussed.

Systematic Nonuniformity Analysis of Amorphous Silicon-on-Insulator Photonic Microring Resonators

Low temperature deposited hydrogenated amorphous silicon (a-Si:H) is a promising material to fabricate compact photonic-electronic integrated circuits (PICs) in multiple layers. However, high refractive index contrast (HIC) photonic circuits are challenging in fabrication and even smallest deviations of the material quality or manufacturing have huge impact on the system performance. We present a systematic study of intrawafer nonuniformity and wafer-to-wafer reproducibility of low-loss a-Si:H and investigate the spectral disorder of photonic microring resonators (MRRs). Photonic MRRs in various spatial configurations, different mask resolutions, and in multiplexed arrangement were fabricated and the spectral disorder in resonance position was examined in within-chip, chip-to-chip, and wafer-to-wafer spectral transmission measurements. The microrings exhibit chip-averaged wafer ranges less than 7.5 nm over 16 chips a 1.5 $\times$ 1.5 cm2 with standard deviations of 220 pm in average for short range systems distanced by a few 100 $\mu$ m. The spatially normalized wafer median of the resonance wavelength spread was determined to be lower 0.7 nm/cm on three wafers. The results demonstrate that a-Si:H PICs are suitable for large-scale integration and the manufacturing quality facilitates low-cost and high throughput assembly-line processing.

Optical Characteristics of Thin Films of In2O3 and ITO

The results of ellipsometric investigations of thin films of In2O3 and In2O3:Sn (90:10%) (ITO) and spectral measurements of the optical transmission are presented. The In2O3 films were obtained by sputtering on Al2O3 [012] substrates with the use of improved magnetron equipment VUP-5M. The ITO films on CEC015S glass substrates were manufactured by PG&O. The thicknesses, refractive indices, and forbidden band gaps of the materials were determined. The obtained values agree with previously described results, indicating that the investigated films are of good quality.

Measuring contact angles of small spherical particles at planar fluid interfaces by Light Extinction

An experimental technique is introduced for measuring the contact angle of small colloidal particles at planar fluid interfaces. The presented light scattering-based method relies on performing two spectral transmittance measurements: one on a particle monolayer standing at the fluid interface and the other on a dispersion of the same particles in a homogeneous medium. The observed shift between the two transmitted spectra is explained in terms of the phase shift parameter, which is then used to determine the particle position relative to the interface and hence the contact angle. The applicability of the technique is demonstrated through simulations and experiments.

Optical Properties of CDS Films by Analysis of Spectral Transmittance

This paper presents the calculation of the optical properties of thin films of CdS from spectral transmittance measurements using the method of Swanepoel. CdS thin film was grown by evaporation technique which has better advantages in optical and crystalline properties compared to other manufacturing techniques as chemical bath deposition (CBD) and sputtering. The experimental procedure is presented for the transmittance spectrum of CdS thin film through a VIS-IR Oriel spectrophotometer that was automated using virtual instrumentation for data acquisition. After applying the mathematical Swanepoel model, the optical properties of the CdS thin film were obtained: 1499,08nm thick, an absorption coefficient of 2x104 cm -1 for a wavelength of 500nm and an optical gap of 2,38eV. These results indicate that the CdS thin film is suitable for use as optical window in the manufacture of solar cells.

Using spectral chlorophyll fluorescence and the photochemical reflectance index to predict physiological dynamics

Abstract Observations of terrestrial chlorophyll fluorescence and the Photochemical Reflectance Index ( PRI ) from space have the potential to improve estimates of global carbon exchange. However the relationship between photosynthetic rate and these measurements is complicated by several factors that relate to the dissipation of absorbed light energy via both photochemical (photosynthesis) and non-photochemical pathways. Numerical simulations of physiological remote sensing signals require the coupling of physically-based radiative transfer models with models of physiological dynamics. These schemes provide the quantitative frameworks from which physiological information can be extracted from remote sensing observations of vegetation, helping to resolve the aforementioned complexities. We present such a framework that links physiological fluorescence theory with spectral remote sensing type measurements at the leaf scale. We show how a simple expression can be used to predict the quantum yield of photochemistry (Φ PSII ), a proxy for photosynthetic efficiency, from spectral measurements and modelled non-photochemical quenching ( NPQ ). We tested two alternate models of NPQ ; one process-based ( PHOTOII ) and the other empirical, based on visible region reflectance changes (the PRI ). We used a Monte Carlo Radiative Transfer ( MCRT ) model to retrieve the separated yields of chlorophyll fluorescence from photosystems II and I. Measurements of dynamic spectral fluorescence, the PRI , hemispherical reflectance and transmittance, saturation pulse integrated fluorescence and pigment contents were collected from maple leaves and used to calibrate and validate the modelling framework. Both NPQ models reproduced the observed photochemical and non-photochemical dynamics. Future work is recommended to scale the framework across space, time and species.

Effect of thickness on physico-chemical properties of p-NiO (bunsenite) thin films prepared by the chemical spray pyrolysis (CSP) technique

P-type NiO thin films have been prepared by spray pyrolysis technique using nickel acetate Ni(CH3COO)2·4H2O as the starting precursor at 450°C. NiO films were deposited with the aim of studying structural, phase evolution, optical, electrical and surface morphological property modifications with thickness. Prior to deposition, non-isothermal decomposition of nickel acetate tetrahydrate was studied using thermogravimetry and differential thermal analysis to get favorable temperature range for the formation of the title compound. Films were prepared for three different thicknesses in the μm range. Prepared films using 0.2M precursor for the thickness 0.316μm were amorphous while those deposited for the thickness 0.441μm were single phase with polycrystalline cubic lattice (a=4.194Å). Broad absorption bands in the low wavenumber finger print region 820–400cm−1 have been assigned to the bonding between Ni and O. From spectral transmittance measurements and using Swanepoel's equations, the optical constants have been evaluated over the entire wavelength range 250–1000nm. NiO film with low resistivity (4.34Ωcm) was achieved which has higher carrier concentration of 0.117×1024m–3 with mobility in the order of 10−5m2/Vs. Atomic force microscopy measurements showed that the RMS surface roughness was 6.21nm, which is the lowest reported value for the NiO films.

Assessment of disease activity in patients with rheumatoid arthritis using optical spectral transmission measurements, a non-invasive imaging technique

ObjectivesIn rheumatoid arthritis (RA), treat-to-target strategies require instruments for valid detection of joint inflammation. Therefore, imaging modalities are increasingly used in clinical practice. Optical spectral transmission (OST) measurements are non-invasive...

Failure causes and mechanisms of retrofit LED lamps

This paper describes one of the first studies of the degradation of retrofit light bulbs based on white GaN light emitting diodes. The results indicate that the lifetime of LED lamps depends mostly on the stability of the driver and optical elements, rather than on the degradation of the LED chips, that have a stable output over stress time. By comparing lamps from four different manufacturers stressed at room and high temperature, we found that (i) long-term stress causes a change of the chromatic properties of the lamps, which is ascribed to the degradation of the phosphors or to the inner LED reflector; (ii) during aging the LED driver may degrade gradually and/or catastrophically, causing a reduction of the output optical power, or a complete failure; (iii) proper thermal management and heat dissipation reduce the degradation rate; (iv) spectral transmissivity measurements and visual inspection reveal the degradation of the diffusive optical elements, which is induced by the short wavelength side of the LED emission spectrum.

Broadband spectral transmittance measurements of complex thin-film filters with optical densities of up to 12.

A new transmittance measurement setup, based on the use of a tunable laser source and a low-noise scientific-grade CCD camera operating in perfect integration mode, is proposed to achieve the spectrally resolved characterization of thin-film filters with optical densities from 0 to 12 in a wavelength range between 400 and 1000nm. The first experimental results obtained on dedicated components demonstrate the efficiency of this new measurement scheme.

Plasma absorption evidence via chirped pulse spectral transmission measurements

This work aims at highlighting the plasma generation dynamics and absorption when a Bessel beam propagates in glass. We developed a simple diagnostics allowing us to retrieve clear indications of the formation of the plasma in the material, thanks to transmission measurements in the angular and wavelength domains. This technique featured by the use of a single chirped pulse having the role of pump and probe simultaneously leads to results showing the plasma nonlinear absorption effect on the trailing part of the pulse, thanks to the spectral-temporal correspondence in the measured signal, which is also confirmed by numerical simulations.

Inkjet printing of resistively loaded FSS for microwave absorbers

Inkjet printing is proposed as a means to create the resistively loaded elements of a frequency selective surface (FSS) which suppresses radar backscatter when placed above a metal ground plane. Spectral transmission and reflection measurements from 9 to 18 GHz show that the dot density of the printed features and the volume ratio of an aqueous vehicle and nano-silver (Ag) ink mixture can be selected to obtain surface resistances in the range 1.2–200 Ω/sq.

A spectral method for discriminating thermodynamic phase and retrieving cloud optical thickness and effective radius using transmitted solar radiance spectra

Abstract. A new retrieval scheme for cloud optical thickness, effective radius, and thermodynamic phase was developed for ground-based measurements of cloud shortwave solar spectral transmittance. Fifteen parameters were derived to quantify spectral variations in shortwave transmittance due to absorption and scattering of liquid water and ice clouds, manifested by shifts in spectral slopes, curvatures, maxima, and minima. To retrieve cloud optical thickness and effective particle radius, a weighted least square fit that matched the modeled parameters was applied. The measurements for this analysis were made with the ground-based Solar Spectral Flux Radiometer in Boulder, Colorado, between May 2012 and January 2013. We compared the cloud optical thickness and effective radius from the new retrieval to two other retrieval methods. By using multiple spectral features, we find a closer fit (with a root mean square difference over the entire spectra of 3.1% for a liquid water cloud and 5.9% for an ice cloud) between measured and modeled spectra compared to two other retrieval methods which diverge by a root mean square of up to 6.4% for a liquid water cloud and 22.5% for an ice cloud. The new retrieval introduced here has an average uncertainty in effective radius (± 1.2 μm) smaller by factor of at least 2.5 than two other methods when applied to an ice cloud.

Particle Size Distribution of E-Cigarette Aerosols and the Relationship to Cambridge Filter Pad Collection Efficiency

AbstractThe relatively volatile nature of the particulate matter fraction of e-cigarette aerosols presents an experimental challenge with regard to particle size distribution measure-ments. This is particularly true for instruments requiring a high degree of aerosol dilution. This was illustrated in a previous study, where average particle diameters in the 10-50 nm range were determined by a high-dilution, electrical mobility method. Total particulate matter (TPM) masses calculated based on those diameters were orders of magnitude smaller than gravimetrically determined TPM. This discrepancy was believed to result from almost complete particle evaporation at the dilution levels of the electrical mobility analysis. The same study described a spectral transmission measurement of e-cigarette particle size in an undiluted state, and reported particles from 210-380 nm count median diameter. Observed particle number concentrations were in the 10Described here is a study in which e-cigarette aerosols were collected on Cambridge filters with adsorbent traps placed downstream in an effort to capture any material passing through the filter. Amounts of glycerin, propylene glycol, nicotine, and water were quantified on the filter and downstream trap. Glycerin, propylene glycol, and nicotine were effciently captured (> 98%) by the upstream Cambridge filter, and a correlation was observed between filtration efficiency and the partial vapor pressure of each component. The present analysis was largely inconclusive with regard to filter efficiency and particle-vapor partitioning of water. [Beitr. Tabakforsch. Int. 26 (2014) 183-190]

Optical transmission properties of Pentelic and Paros marble.

Ancient Greek and Roman sources report that the statue of Zeus in Olympia had a head, and in particular eyes, similar to the description of Zeus by Homer, so we think that the statue was visible to the human eye. Since the temple was 12m high, and had a small door and no windows, the illumination of the statue by conventional media is questionable. The aim of this paper is to characterize the optical transmission of Paros and Pentelic marble to demonstrate that it was possible to have the Zeus temple illuminated through the roof marble tiles. Spectral absolute transmittance measurements were taken in samples with different thicknesses using a calibrated spectrophotometer, as well as total transmittance measurements using a luxmeter. The results show that both types of marble transmit light and that Pentelic marble has a higher transmittance in the visible range than Paros marble in some cases and hence could have been one reason, among others, to change the type of marble in the roof in antiquity.

Photocatalytic inactivation of bacterial spores using TiO2 films with silver deposits

The present work evaluates the enhancement of the photocatalytic inactivation of bacterial spores employing TiO2 films with silver deposits compared to TiO2 films without metal deposition. Bacillus subtilis spores spread over TiO2 films with different silver contents were irradiated with artificial UV-A light. The performances of the coatings were evaluated by the quantum efficiency parameter, which relates the inactivation rate with the radiation absorption rate by the coating. Spectral diffuse transmittance and reflectance measurements of the films were carried out to evaluate the fraction of energy absorbed by the coatings. TiO2 and Ag/TiO2 films characterization also included X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Scanning Electron Microscopy (SEM). A notable increase in the photocatalytic inactivation was observed by increasing the silver content of the coatings, reaching a maximum quantum efficiency with the sample containing 1.09wt.% Ag/TiO2. The addition of higher amounts of silver rendered lower inactivation, thus indicating the existence of an optimum Ag/TiO2 relation.