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- Brno University of Technology
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- Institut National Polytechnique Felix Houphou?t-Boigny Yamoussoukro
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Numerical simulation of light propagation in metal-coated SNOM tips
摘要： Presented are the results of numerical simulations accomplished to investigate the propagation of electromagnetic excitations in certain types of metal-coated tapered tips terminating SiO2 multimode optical fibres with a subwavelength output aperture. The numerical simulations were initiated in order to enable better interpretation of previously reported experimental results concerning some features of the mesoscopic effect of spectral modulation observed for a broadband light transmitted by such tips. This effect occurs due to the interference between a small number of waveguide modes exiting a metal-coated tip, and the experimental results indicate a possible mode-selective photon-plasmon coupling in the studied tips. To match the experimental conditions, the tips were modelled for the light wavelength of 800 nm as three-layer systems (with the intermediate adhesion Cr layer and the outer layer of Al or Au). However, due to computational restrictions the end of a tip, only 18 μm long (most significant), was modelled. Numerical simulations yielded the dependences of propagation and attenuation constants on the fibre core radius for the most intensive (both photonic and plasmonic) output modes. The pairs of modes most probably contributing to the observed spectral modulation were identified. Although the simulations did not reveal any explicit mode coupling, the imperfections of real tips can cause mode transformations implying possible involvement of more than two modes. The thin (20 nm) Cr layer plays the main role for plasmonic modes generated on its SiO2 interface, which explains the small outer metal layer influence on the observed modal dispersion.
关键词： numerical simulation,multimode optical fibre,optics,spectral modulation,SNOM tip,plasmonics,photonics
更新于2025-09-04 15:30:14
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A Method to Reconstruct the Solar-Induced Canopy Fluorescence Spectrum from Hyperspectral Measurements
摘要： A method for canopy Fluorescence Spectrum Reconstruction (FSR) is proposed in this study, which can be used to retrieve the solar-induced canopy fluorescence spectrum over the whole chlorophyll fluorescence emission region from 640–850 nm. Firstly, the radiance of the solar-induced chlorophyll fluorescence (Fs) at five absorption lines of the solar spectrum was retrieved by a Spectral Fitting Method (SFM). The Singular Vector Decomposition (SVD) technique was then used to extract three basis spectra from a training dataset simulated by the model SCOPE (Soil Canopy Observation, Photochemistry and Energy fluxes). Finally, these basis spectra were linearly combined to reconstruct the Fs spectrum, and the coefficients of them were determined by Weighted Linear Least Squares (WLLS) fitting with the five retrieved Fs values. Results for simulated datasets indicate that the FSR method could accurately reconstruct the Fs spectra from hyperspectral measurements acquired by instruments of high Spectral Resolution (SR) and Signal to Noise Ratio (SNR). The FSR method was also applied to an experimental dataset acquired in a diurnal experiment. The diurnal change of the reconstructed Fs spectra shows that the Fs radiance around noon was higher than that in the morning and afternoon, which is consistent with former studies. Finally, the potential and limitations of this method are discussed.
关键词： Fluorescence Spectrum Reconstruction (FSR),solar-induced chlorophyll fluorescence (Fs),Spectral Fitting Method (SFM),Fraunhofer Line Discriminator (FLD),hyperspectral remote sensing,Singular Vector Decomposition (SVD)
更新于2025-09-04 15:30:14
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Assessing the Reliability of Thermal and Optical Imaging Techniques for Detecting Crop Water Status under Different Nitrogen Levels
摘要： Efficient management of irrigation water is fundamental in agriculture to reduce the environmental impacts and to increase the sustainability of crop production. The availability of adequate tools and methodologies to easily identify the crop water status in operating conditions is therefore crucial. This work aimed to assess the reliability of indices derived from imaging techniques—thermal indices (Ig (stomatal conductance index) and CWSI (Crop Water Stress Index)) and optical indices (NDVI (Normalized Difference Vegetation Index) and PRI (Photochemical Reflectance Index))—as operational tools to detect the crop water status, regardless the eventual presence of nitrogen stress. In particular, two separate experiments were carried out in a greenhouse, on two spinach varieties (Verdi F1 and SV2157VB), with different microclimatic conditions and under different levels of water and nitrogen application. Statistical analysis based on ANOVA test was carried out to assess the independence of thermal and optical indices from the crop nitrogen status. These imaging indices were successively compared through correlation analysis with reference destructive and non-destructive measurements of crop water status (stomatal conductance, chlorophyll a fluorescence, and leaf and soil water content), and linear regression models of thermal and optical indices versus reference measurements were calibrated. All models were significant (Fisher p-value lower than 0.05), and the highest R2 values (greater than 0.6) were found for the regression models between CWSI and the soil water content, NDVI and the leaf water content, and PRI and the stomatal conductance. Further analysis showed that imaging indices acquired by thermal cameras (especially CWSI) can be used as operational tools to detect the crop water status, since no dependence on plant nitrogen conditions was observed, even when the soil water depletion was very limited. Our results confirmed that imaging indices such as CWSI, NDVI and PRI can be used as operational tools to predict soil water status and to detect drought stress under different soil nitrogen conditions.
关键词： crop water status,crop water stress prediction,optical imaging sensor,thermal camera,spectral imaging index
更新于2025-09-04 15:30:14
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Identification of photospheric activity features from SOHO/MDI data using the ASAP tool
摘要： The variation of solar irradiance is one of the natural forcing mechanisms of the terrestrial climate. Hence, the time-dependent solar irradiance is an important input parameter for climate modelling. The solar surface magnetic field is a powerful proxy for solar irradiance reconstruction. The analyses of data obtained with the Michelson Doppler Imager (MDI) on board the SOHO mission are therefore useful for the identification of solar surface magnetic features to be used in solar irradiance reconstruction models. However, there is still a need for automated technologies that would enable the identification of solar activity features from large databases. To achieve this we present a series of enhanced segmentation algorithms developed to detect and calculate the area coverages of specific magnetic features from MDI intensitygrams and magnetograms. These algorithms are part of the Automated Solar Activity Prediction (ASAP) tool. The segmentation algorithms allow us to identify the areas on the solar disk covered by magnetic elements inside and outside boundaries of active regions. Depending on their contrast properties, magnetic features within an active region boundary are classified as sunspot umbra and penumbra, or faculae. Outside an active region boundary magnetic elements are identified as network. We present the detailed steps involved in the segmentation process and provide the area coverages of the segmented MDI intensitygrams and magnetograms. The feature segmentation was carried out on daily intensitygrams and magnetograms from April 21, 1996 to April 11, 2011. This offers an exciting opportunity to undertake further investigations that benefit from solar features segmentations, such as solar irradiance reconstruction, which we plan to investigate in the future.
关键词： Magnetogram,Sunspot,Solar image processing,Spectral irradiance,Active region
更新于2025-09-04 15:30:14
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Accuracy of Calcium Scoring calculated from contrast-enhanced Coronary Computed Tomography Angiography using a dual-layer spectral CT: A comparison of Calcium Scoring from real and virtual non-contrast data
摘要： Modern non-invasive evaluation of Coronary Artery Disease (CAD) requires non-contrast low dose Computed Tomography (CT) imaging for determination of Calcium Scoring (CACS) and contrast-enhanced imaging for evaluation of vascular stenosis. Several methods for calculation of CACS from contrast-enhanced images have been proposed before. The main principle for that is generation of virtual non-contrast images by iodine subtraction from a contrast-enhanced spectral CT dataset. However, those techniques have some limitations: Dual-Source CT imaging can lead to increased radiation exposure, and switching of the tube voltage (rapid kVp switching) can be associated with slower rotation speed of the gantry and is thus prone to motion artefacts that are especially critical in cardiac imaging. Both techniques cannot simultaneously acquire spectral data. A novel technique to overcome these difficulties is spectral imaging with a dual-layer detector. After absorption of the lower energetic photons in the first layer, the second layer detects a hardened spectrum of the emitted radiation resulting in registration of two different energy spectra at the same time. The objective of the present investigation was to evaluate the accuracy of virtual non-contrast CACS computed from spectral data in comparison to standard non-contrast imaging.
关键词： virtual non-contrast data,Coronary Computed Tomography Angiography,Calcium Scoring,dual-layer spectral CT
更新于2025-09-04 15:30:14
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Raman spectroscopy for kidney tissue and its neoplasms research
摘要： This work is devoted to the study of the spectral properties of intact and tumor kidney tissues. For excitation of Raman scattering and autofluorescence a laser with a wavelength of 785 nm was used. Visually and morphologically unchanged tissues of pig and human kidneys as well as tumor tissue of human kidneys were used as the test samples. The analysis of registered signals was carried out using the method of projection on latent structures to isolate the spectral features between tissue types. The study showed a difference between the registered signals of the clear cell adenocarcinoma and chromophobe types of human kidney cancer, the most informative bands of the Raman spectrum for the determination of the clear cell human kidney cancer were 330-500 cm-1, 870-980 cm-1, 980-1130 cm-1, 1230-1270 cm-1, 1360 -1420 cm-1.
关键词： spectral properties,autofluorescence,neoplasms,kidney tissue,Raman spectroscopy
更新于2025-09-04 15:30:14
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[Papers] A Multi Spectral Imaging System with a 71dB SNR 190-1100 nm CMOS Image Sensor and an Electrically Tunable Multi Bandpass Filter
摘要： This paper demonstrates a multi spectral imaging system utilizing a linear response, high signal to noise ratio (SNR) and wide spectral response CMOS image sensor (CIS), and an electrically tunable multi bandpass optical filter with narrow full width at half maximum (FWHM) of transmitted waveband. The developed CIS achieved 71dB SNR, 1.5 × 107 e– full well capacity (FWC), 190-1100nm spectral response with very high quantum efficiency (QE) in near infrared (NIR) waveband using low impurity concentration Si wafer (~1012 cm-3). With the developed CIS, diffusion of 5mg/dl glucose into physiological saline solution, as a preliminary experiment for non-invasive blood glucose measurement, was successfully visualized under 960nm and 1050nm wavelengths, at which absorptions of water molecules and glucose appear among UV to NIR waveband, respectively.
关键词： bandpass filter,CMOS image sensor,FWC,multi spectral imaging,SNR,absorption analysis
更新于2025-09-04 15:30:14
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Partial Differential Phase Shift Keying – Theory and Motivation
摘要： Recently it was demonstrate that partial Differential Phase Shift Keying (i.e., when the delay inside the Delay Interferometer is shorter than the symbol period) can partially compensate the signal deformation caused by spectrally narrowing the optical channel (by interleavers, add-drop elements, Wavelength Division Multiplexing filters, etc.). In this paper the source of this effect is investigated with numerical simulations and, to the best of our knowledge for the first time, analytically. We found that our analytical analysis matched the simulation results with high accuracy. Furthermore, a phenomenological relation, which relates the optimum Free Spectral Range to the channel bandwidth, was derived.
关键词： Differential Phase Shift Keying,Free Spectral Range,Delay Interferometer,fiber optics
更新于2025-09-04 15:30:14
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High‐ and Ultra‐High definition of IR spectral histopathology gives an insight into chemical environment of lung metastases in breast cancer
摘要： Using high- (HD) and ultra-high-definition (UHD) of Fourier Transform Infrared (FTIR) spectroscopic imaging, we characterised spectrally pulmonary metastases in a murine model of breast cancer comparing them with histopathological results (H&E staining). This comparison showed excellent agreement between the methods in case of localisation of metastases with size below 1 mm and revealed that label-free HD and UHD IR spectral histopathology distinguish the type of neoplastic cells. We primary focused on differentiation between metastatic foci in the pleural cavity from cancer cells present in lung parenchyma and inflamed cells present in extracellular matrix of lungs due to growing of advanced metastases. In addition, a combination of unsupervised clustering and IR imaging indicated the high sensitivity of FTIR spectroscopy to identify chemical features of small macrometastases located under the pleural cavity and during epithelial–mesenchymal transition (EMT). FTIR based spectral histopathology was proved to detect not only phases of breast cancer metastasis to lungs but also to differentiate various origins of metastases seeded from breast cancer.
关键词： pulmonary metastases,high and ultra-high definition of FTIR imaging,spectral histopathology,breast cancer,unsupervised clustering
更新于2025-09-04 15:30:14
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[IEEE 2018 International Conference on Advances in Computing, Communications and Informatics (ICACCI) - Bangalore, India (2018.9.19-2018.9.22)] 2018 International Conference on Advances in Computing, Communications and Informatics (ICACCI) - Multi-Modal Medical Image Fusion Using Curvelet Algorithm
摘要： Medical image fusion is the process of combining images from different modalities to make the fused image more informative than any of the source images. Images of different modalities include PET, CT, SPECT and MRI. One input image will have high spatial resolution and low spectral information and another image will have high spectral resolution and vice versa. The aim of medical image fusion is to have a single image having both spatial and spectral resolution. Most commonly used transform domain methods like Curvelet transform is applied to extract more specific information from the source images. Experimental results demonstrate that fused image will have sharpened image resolution and the fusion performance is evaluated with image quality assessment metrics.
关键词： SPECT/PET,MRI,spatial and spectral resolution,Curvelet
更新于2025-09-04 15:30:14