1,721,080 research outputs found
Enhanced light backscattering in thermally poled plasmonic nanocomposite and its application to vapour sensing
No full textWe show theoretically that gold nanoparticles embedded in glass can exhibit enhanced light backscattering in presence of leaky waveguide and report on selective vapour sensing in thermally poled nanocomposite in which this concept is implemented
Optimizing irrigation water use efficiency for tomato and maize fields across italy combining remote sensing data and the aquacrop model
Full text linkRemote sensing data of canopy cover and leaf area index are used together with the AquaCrop model to optimize irrigation water use efficiency for tomato and maize fields across Italy, which differ in climate, soil types and irrigation technique. An optimization irrigation strategy, “SIM strategy”, is developed based on crop stress thresholds and then applied to all the analyzed fields in different crop seasons, evaluating the effect not only on irrigation volume and number of irrigations but also on crop yield and canopy cover, and on the drainage flux which represents the main water loss. Irrigation volume reduction is found to be between 200 and 1000 mm, mainly depending on the different soil types within the climate, irrigation technique and crop type. This is directly related to the drainage flux reduction which is of a similar entity. The SIM strategy efficiency has then been quantified by different indicators, such as the irrigation water use efficiency (IWUE) which is higher than with the observed irrigations (around 35% for tomato fields in Southern Italy, between 30 and 80% for maize in Northern Italy), and the percolation deficit and irrigation efficiency. The AquaCrop model has been previously calibrated against canopy cover and leaf area index (LAI) data, producing errors between 0.7 and 5%, while absolute mean errors (MAE) between 0.015 and 0.04 are obtained for soil moisture (SM). The validation of the AquaCrop model has been performed against evapotranspiration (ET) ground-measured data and crop yields producing MAE values ranging from 0.3 to 0.9 mm/day, and 0.9 ton/ha for maize and 10 ton/ha for tomatoes, respectively
Effect of the three gorges dam on total suspended sediments from modis and landsat satellite data
Full text linkTotal suspended matter (TSM) concentration is an extremely important parameter for water quality definition. The aim of this work is the evaluation of the effect of the Three Gorges Dam on total suspended sediments using remote sensing data at different temporal and spatial resolutions. TSM is estimated for the middle Yangtze river, China, before and after the construction of the Three Gorges Dam. The retrieved values are correlated to ground daily discharge values, finding relations between the physical quantities and discharge. Then, the application of the obtained relations to the discharge dataset provides continuous daily estimations of TSM values, also covering the days for which satellite scenes were lacking. This daily dataset will allow us to estimate the annual volume of river solid sediments. According to this work, both low spatial resolution MODIS (Moderate Resolution Imaging Spectroradiometer) data and high-resolution. Landsat 5 and 7 are able to detect the changes in TSM distribution over space and time induced by the building of the Three Gorges Dam, with a variation of even 50 mg/L over summer season. The confrontation of solid discharge with daily estimated TSM values shows that the single band MODIS algorithm performs better for medium-low concentrations, while the dual-band algorithm for MODIS and the selected Landsat algorithm perform better with high concentrations
Femtosecond laser direct-writing and poling of embedded grating structures
No full textIn recent years, the use of a focused femtosecond laser to directly write structures deep within transparent media has attracted much attention due to its ability to write in three-dimensions [1]. By utilizing an amplified Ti:sapphire laser (pulse duration 150fs, repetition rate 250kHz, λ=850nm), we have developed a novel technique that enables us to write grating structures within the bulk of an optical fiber through its cleaved face, allowing control over light subsequently exiting the fiber. Fig 1(a) shows a microscope image of an embedded diffraction grating having a 5µm pitch and buried 25µm below a fiber's cleaved face. Fig 1(b) displays a far-field pattern created by a single-mode fiber which has a two-dimensional grating written 5µm below its cleaved face. The controllability of the power and direction of diffracting orders offers tantalizing opportunities for new methods of optical routing. A further grating of 20µm period and 4µm line width has been directly-written into a silica glass plate (Herasil 1). Thermal poling was carried out on the plate in air for 15 minutes at 280°C with 4kV applied [2]. After poling the grating was investigated using a Nd:YAG laser (λ=1064nm), with a focused spot sue of 20µm. The second harmonic was subsequently imaged by CCD camera. Fig 2(a) shows the second harmonic produced in a Gaussian beam away from the grating region as expected. However, Fig 2(b) shows the second harmonic produced at the position of the irradiated lines to be much stronger indicating that the χ(2) is larger in the Ti:Sapphire irradiated regions. The incident beam is large enough to encompass two grating lines as indicated by the arrows. In Fig 2(a) the brightness is enhanced compared to Fig 2(b) to make the spot visible. By direct-writing periodic structures into silica fibers from the side and subsequent poling, work is currently underway to investigate the feasibility of achieving efficient quasi-phase-matching in silica fibres [3]. Fig.1. (a) A 5µm period diffraction grating written 25µm below a fiber's cleaved face. (b) Far-field pattern of single-mode light exiting a fiber containing an embedded 2-d grating. Fig.2. Imaging of the SHG (a) Inclined incidence and well away from the grating. (b) Inclined incidence and on the grating
Channel waveguide lasers produced by femtosecond and picosecond direct laser writing in Ti:sapphire crystals
No full textFemtosecond-laser-written Ti:sapphire channel waveguides lase at ~798.25 nm above a threshold pump power of 84 mW with output power and slope efficiency of 143 mW and 23.5%, respectively. Lasing was also observed in picosecond-laser-written channels
Poling of glass modified by femtosecond irradiation
No full textThermal poling of silica glass modified by femtosecond laser irradiation has been demonstrated. Evidence of second-order nonlinearity modulation between the treated and non-treated regions has been observed. The technique was used for χ(2) grating fabrication
T:sapphire channel waveguide lasers produced by femtosecond and picosecond laser writing
No full textUltra-short pulse laser writing is a widely adopted method for rapid prototyping of channel waveguide lasers and amplifiers in the bulk of different types of transparent glasses, crystals and ceramic materials [1, 2]. The writing process in laser crystals relies on engineering either depressed-cladding structures or two parallel tracks to confine the mode in the spacing in-between, by stress-induced increases in the refractive index. Ti:sapphire (a-Al2O3:Ti3+) with its broad emission bandwidth (650-1100 nm) is a benchmark solid-state gain medium for ultrashort laser pulse generation and broadly tuneable lasers. Here, we report on the continuous wave (cw) laser operation of Ti:sapphire channel waveguides fabricated by fs- and picosecond (ps) laser writing
Second-harmonic vortex generation with a poled glass
No full textA Simple method for nonlinear vortex generation is presented. Spin-to-Orbital transfer with total angular momentum conservation between photons at the fundamental and at the second-harmonic frequency is demonstrated
Second-order optical nonlinearity induced in high-index bismuthate glass by thermal poling
No full textSecond-order optical nonlinearity was induced in Bi content was increased from 6.25 mol% to 25.0 mol%. The formation of the nonlinearity was found to depend critically on poling temperature and time, sample thickness and glass-electrode contact
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