We report a non-destructive characterization of planar two-dimensional （2D） photonic crystals （PhCs） made in silicon on insulator （SOI） wafers using ellipsometric or Fourier transformed infrared （FTIR） spectro...We report a non-destructive characterization of planar two-dimensional （2D） photonic crystals （PhCs） made in silicon on insulator （SOI） wafers using ellipsometric or Fourier transformed infrared （FTIR） spectroscope. At large wavelengths, devices behave as homogeneous isotropic materials defined by an effective filling factor. The experimental results related to the PhC limited dimensions confirm this characterization.展开更多
A mathematical model of the determination of the iron in water using the method of primary secondary wavelengths was proposed.According to the relation between absorbance (A) and the wavelength of the irradiation lig...A mathematical model of the determination of the iron in water using the method of primary secondary wavelengths was proposed.According to the relation between absorbance (A) and the wavelength of the irradiation light(λ) and the iron(x) in water,a way with high accuracy to determine the iron in water was investigated.The calculation curve is stable and hardly affected by environmental conditions.Experiments with water samples have shown that the detection limit was 0.015μg·ml -1 ,RSD≤3.5%,and the recovery rate was 95.4%～101.6%.展开更多
We utilize the temperature profiles with a height resolution of 50-m obtained over the Beijing Observatory in the period between January of 2002 and December of 2002 to study vertical wavenumber spectra of normalized ...We utilize the temperature profiles with a height resolution of 50-m obtained over the Beijing Observatory in the period between January of 2002 and December of 2002 to study vertical wavenumber spectra of normalized temperature fluctuations in the 1.67-8.02 km and 13.57-19.92 km altitude ranges and compare them with linear saturation model.Results indicate that individual vertical wavenumber spectra reveal a considerable variability in both slope and amplitude.The observed variability is not consistent with the predictions of linear saturation model.However,mean vertical wavenumber spectra in the troposphere measured at different seasons and different local times show great similarities with fairly uniform negative slopes of ～3.0 and amplitudes proportional to N 4,suggesting that the seasonal mean spectra observed in the troposphere completely obey the linear saturation model and are unique at present.In contrast,while the spectral slopes of the mean vertical wavenumber spectra in the lower stratosphere tend to support the explanation of the observed temperature fluctuations by linear saturation model,the spectral amplitudes diverge significantly from linear saturation model,suggesting that the seasonal mean spectra in the lower stratosphere do not obey the linear saturation model and are unique at present.The dominant vertical wavelengths derived from the observed mean vertical wavenumber spectra are estimated to be ～3.2-～2.1 km in the troposphere and lower stratosphere,which is generally consistent with those reported in the literature.展开更多
Using the approximation of constant pressure, a thermodynamic identity for GR as given by Padmanabhan is applied to early universe graviton production. We build upon an earlier result in doing this calculation. Previo...Using the approximation of constant pressure, a thermodynamic identity for GR as given by Padmanabhan is applied to early universe graviton production. We build upon an earlier result in doing this calculation. Previously, we reviewed a relationship between the magnitude of an inflaton, the resultant potential, GW frequencies and also Gravitational waves, GW, wavelengths. The Non Linear Electrodynamics (NLED) approximation makes full use of the Camara et al. result about density and magnetic fields to ascertain when the density is positive or negative, meaning that at a given magnetic field strength, if one uses a relationship between density and pressure at the start of inflation one can link the magnetic field to pressure. From there an estimated initial temperature is calculated. This temperature scales down if the initial entropy grows.展开更多
By coupling a train of femtosecond pulses with 100 fs pulse width at a repetition rate of 76 MHz generated by a mode-locked Ti： sapphire laser into the fundamental mode of photonic crystal fibre （PCF） with central ...By coupling a train of femtosecond pulses with 100 fs pulse width at a repetition rate of 76 MHz generated by a mode-locked Ti： sapphire laser into the fundamental mode of photonic crystal fibre （PCF） with central holes fabricated through extracting air from the central hole, the broad and ultra-flattened supercontinuum （SC） in the visible wavelengths is generated. When the fundamental mode experiences an anomalous dispersion regime, three phases in the SC generation process are primarily presented. The SC generation （SCG） in the wavelength range from 470 nm to 805 nm does not emerge significant ripples due to a higher pump peak power and the corresponding mode fields at different wavelengths are observed using Bragg gratings. The relative intensity fluctuations of output spectrum in the wavelength ranges of 530 nm to 640 nm and 543 nm to 590 nm are only 0.028 and 0.0071, respectively.展开更多
This study was carried out to analyze the spectral reflectance response of different nitrogen levels for corn crops.Four different nitrogen treatments of 0%,80%,100%and 120%BMP(best management practice)were studied.Pr...This study was carried out to analyze the spectral reflectance response of different nitrogen levels for corn crops.Four different nitrogen treatments of 0%,80%,100%and 120%BMP(best management practice)were studied.Principal component analysis-loading(PCA-loading)was used to identify the effective wavelengths.Partial least squares(PLS)and multiple linear regression(MLR)models were built to predict different nitrogen values.Vegetation indices(VIs)were calculated and then used to build more prediction models.Both full and selected wavelengths-based models showed similar prediction trends.The overall PLS model obtained the coefficient of determination(R^(2))of 0.6535 with a root mean square error(RMSE)of 0.2681 in the prediction set.The selected wavelengths for overall MLR model obtained the R^(2) of 0.6735 and RMSE of 0.3457 in the prediction set.The results showed that the wavelengths in visible and near infrared region(350-1000 nm)performed better than the two either spectral regions(1001-1350/1425-1800 nm and 2000-2400 nm).For each data set,the wavelengths around 555 nm and 730 nm were identified to be the most important to predict nitrogen rates.The vogelmann red edge index 2(VOG 2)performed the best among all VIs.It demonstrated that spectral reflectance has the potential to be used for analyzing nitrogen response in corn.展开更多
Estimation of leaf chlorophyll content(LCC) by proximal sensing is an important tool for photosynthesis evaluation in high-throughput phenotyping. The temporal variability of crop biochemical properties and canopy str...Estimation of leaf chlorophyll content(LCC) by proximal sensing is an important tool for photosynthesis evaluation in high-throughput phenotyping. The temporal variability of crop biochemical properties and canopy structure across different growth stages has great impacts on wheat LCC estimation, known as growth stage effects. It will result in the heterogeneity of crop canopy at different growth stages, which would mask subtle spectral response of biochemistry variations. This study aims to explore spectral responses on the growth stage effects and establish LCC models suited for different growth stages. A total number of 864 pairwise samples of wheat canopy spectra and LCC values with 216 observations of each stage were sampled at the tillering, jointing, booting and heading stages in 2021. Firstly, statistical analysis of LCC and spectral response presented different distribution traits and typical spectral variations peak at 470, 520 and 680 nm. Correlation analysis between LCC and reflectance showed typical red edge shifts. Secondly, the testing model of partial least square(PLS) established by the entire datasets to validate the predictive performance at each stage yielded poor LCC estimation accuracy. The spectral wavelengths of red edge(RE) and blue edge(BE) shifts and the poor estimation capability motivated us to further explore the growth stage effects by establishing LCC models at respective growth periods.Finally, competitive adaptive reweighted sampling PLS(CARS-PLS), decision tree(DT) and random forest(RF) were used to select sensitive bands and establish LCC models at specific stages. Bayes optimisation was used to tune the hyperparameters of DT and RF regression. The modelling results indicated that CARS-PLS and DT did not extract specific wavelengths that could decrease the influences of growth stage effects. From the RF out-of-bag(OOB) evaluation, the sensitive wavelengths displayed consistent spectral shifts from BE to GP and from RE to RV from tillering to heading stages. Compared with CARS-P展开更多
A novel cascaded DFB laser,which consists of two serial gratings to provide selectable wavelengths,is presented and analyzed by the transfer matrix method.In this method,efficient facet reflectivity is derived from th...A novel cascaded DFB laser,which consists of two serial gratings to provide selectable wavelengths,is presented and analyzed by the transfer matrix method.In this method,efficient facet reflectivity is derived from the transfer matrix built for each serial section and is then used to simulate the performance of the novel cascaded DFB laser through self-consistently solving the gain equation,the coupled wave equation and the current continuity equations.The simulations prove the feasibility of this kind of wavelength selectable laser and a corresponding designed device with two selectable wavelengths of 1.51μm and 1.53μm is realized by experiments on InP-based multiple quantum well structure.展开更多
We numerically study the propagation dynamics of intense optical pulses in gas-filled hollow-core fibers（HCFs）. The spatiotemporal dynamics of the pulses show a transition from tightly confined to loosely confined c...We numerically study the propagation dynamics of intense optical pulses in gas-filled hollow-core fibers（HCFs）. The spatiotemporal dynamics of the pulses show a transition from tightly confined to loosely confined characteristics as the fiber core is increased, which manifests as a deterioration in the spatiotemporal uniformity of the beam. It is found that using the gas pressure gradient does not enhance the beam quality in large-core HCFs, while inducing a positive chirp in the pulse to lower the peak power can improve the beam quality. This indicates that the self-focusing effect in the HCFs is the main driving force for the propagation dynamics. It also suggests that pulses at longer wavelengths are more suitable for HCFs with large cores because of the lower critical power of self-focusing, which is justified by the numerical simulations. These results will benefit the generation of energetic few-cycle pulses in large-core HCFs.展开更多
A number of researchers haw reported discrepancies between surface resistance （SR） measurements and classical theoretical predictions in normal metals for millimetre wavelengths （MW）. In this paper, a rigorous mod...A number of researchers haw reported discrepancies between surface resistance （SR） measurements and classical theoretical predictions in normal metals for millimetre wavelengths （MW）. In this paper, a rigorous model is developed for analysing SR of normal metals. This model is based on quantum mechanical analysis of the spatial dispersion within the metal. We use the model to predict SR and eliminate the discrepancies between SR measurements and classical theoretical predictions in normal metals for MW. Moreover, we have compared the results of this model with that of the classical skin-effect model and classical relaxation-effect model. Our analysis shows that the conductivity is not only frequency- but also wave-vector-dependent for MW. We demonstrate that our model has good quantitative agreement with the published experimental data for the room temperature surface resistance of normal metals for MW.展开更多
An extensive theoretical set of atomic data for Rb XXIX in a wide range with L-shell electron excitations to the M-shell has been reported. We have computed energy levels for the lowest 113 fine structure levels of Rb...An extensive theoretical set of atomic data for Rb XXIX in a wide range with L-shell electron excitations to the M-shell has been reported. We have computed energy levels for the lowest 113 fine structure levels of Rb XXIX. The fully relativistic multiconfigurational Dirac-Fock method （MCDF） within the framework of Dirac-Coulomb Hamiltonian taking quantum electrodynamics （QED） and Breit corrections into account has been adopted for calculations. Radiative data are reported for electric dipole （El）, magnetic dipole （MI）, electric quadrupole （E2）, and magnetic quadrupole （M2） transitions from the ground level, although calculations have been performed for a much larger number of levels. To assess the accuracy of results, we performed analogous calculations using flexible atomic code （FAC）. Comparisons are made with existing available results and a good agreement has been achieved. Most of the wavelengths calculated lie in the soft x-ray （SXR） region. Lifetimes for all 113 levels have also been provided for the first time. Additionally, we have provided the spectra for allowed transitions from n = 2 to n = 3 within the x-ray region and also compared our SXR photon wavelengths with experimentally recognized wavelengths. We hope that our results will be beneficial in fusion plasma research and astrophysical applications.展开更多
A long-range surface plasmon polariton （LRSPP） waveguide consisting of a 15nm thick gold stripe embedded in a homogeneous polymer BCB is reported. LRSPPs are excited by TM-mode input light successfully using an end-...A long-range surface plasmon polariton （LRSPP） waveguide consisting of a 15nm thick gold stripe embedded in a homogeneous polymer BCB is reported. LRSPPs are excited by TM-mode input light successfully using an end-fire method. By scanning the output coupling fibre, the near field of the LRSPP is measured. The propagation loss of as low as 2.34 dB/mm is demonstrated.展开更多
文摘We report a non-destructive characterization of planar two-dimensional （2D） photonic crystals （PhCs） made in silicon on insulator （SOI） wafers using ellipsometric or Fourier transformed infrared （FTIR） spectroscope. At large wavelengths, devices behave as homogeneous isotropic materials defined by an effective filling factor. The experimental results related to the PhC limited dimensions confirm this characterization.
文摘A mathematical model of the determination of the iron in water using the method of primary secondary wavelengths was proposed.According to the relation between absorbance (A) and the wavelength of the irradiation light(λ) and the iron(x) in water,a way with high accuracy to determine the iron in water was investigated.The calculation curve is stable and hardly affected by environmental conditions.Experiments with water samples have shown that the detection limit was 0.015μg·ml -1 ,RSD≤3.5%,and the recovery rate was 95.4%～101.6%.
基金supported by National Natural Science Foundation of China (Grant Nos.40674088,40621003,40675021)National Important Basic Research Project (Grant No.2006CB806306)the Specialized Research Fund for State Key Laboratories,and Key Lab of Geospace Environment and Geodesy,Ministry of Education of China
文摘We utilize the temperature profiles with a height resolution of 50-m obtained over the Beijing Observatory in the period between January of 2002 and December of 2002 to study vertical wavenumber spectra of normalized temperature fluctuations in the 1.67-8.02 km and 13.57-19.92 km altitude ranges and compare them with linear saturation model.Results indicate that individual vertical wavenumber spectra reveal a considerable variability in both slope and amplitude.The observed variability is not consistent with the predictions of linear saturation model.However,mean vertical wavenumber spectra in the troposphere measured at different seasons and different local times show great similarities with fairly uniform negative slopes of ～3.0 and amplitudes proportional to N 4,suggesting that the seasonal mean spectra observed in the troposphere completely obey the linear saturation model and are unique at present.In contrast,while the spectral slopes of the mean vertical wavenumber spectra in the lower stratosphere tend to support the explanation of the observed temperature fluctuations by linear saturation model,the spectral amplitudes diverge significantly from linear saturation model,suggesting that the seasonal mean spectra in the lower stratosphere do not obey the linear saturation model and are unique at present.The dominant vertical wavelengths derived from the observed mean vertical wavenumber spectra are estimated to be ～3.2-～2.1 km in the troposphere and lower stratosphere,which is generally consistent with those reported in the literature.
文摘Using the approximation of constant pressure, a thermodynamic identity for GR as given by Padmanabhan is applied to early universe graviton production. We build upon an earlier result in doing this calculation. Previously, we reviewed a relationship between the magnitude of an inflaton, the resultant potential, GW frequencies and also Gravitational waves, GW, wavelengths. The Non Linear Electrodynamics (NLED) approximation makes full use of the Camara et al. result about density and magnetic fields to ascertain when the density is positive or negative, meaning that at a given magnetic field strength, if one uses a relationship between density and pressure at the start of inflation one can link the magnetic field to pressure. From there an estimated initial temperature is calculated. This temperature scales down if the initial entropy grows.
基金Project supported by the National Key Basic Research Special Foundation of China(Grant No.2010CB327605 and 2010CB328300)National High-Technology Research and Development Program of China(Grant No.2009AA01Z220)+3 种基金the Key Program of Chinese Ministry of Education(Grant No.109015)the Discipline Co-construction Project of Beijing Municipal Commission of Education(Grant No.YB20081001301)the Open Fund of Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications) of Ministry of Educationthe Specialized Research Fund for the Doctoral Program of Beijing University of Posts and Telecommunications,China(Grant No.CX201023)
文摘By coupling a train of femtosecond pulses with 100 fs pulse width at a repetition rate of 76 MHz generated by a mode-locked Ti： sapphire laser into the fundamental mode of photonic crystal fibre （PCF） with central holes fabricated through extracting air from the central hole, the broad and ultra-flattened supercontinuum （SC） in the visible wavelengths is generated. When the fundamental mode experiences an anomalous dispersion regime, three phases in the SC generation process are primarily presented. The SC generation （SCG） in the wavelength range from 470 nm to 805 nm does not emerge significant ripples due to a higher pump peak power and the corresponding mode fields at different wavelengths are observed using Bragg gratings. The relative intensity fluctuations of output spectrum in the wavelength ranges of 530 nm to 640 nm and 543 nm to 590 nm are only 0.028 and 0.0071, respectively.
基金This work was supported by University of Minnesota Informatics Institute(UMII)on the Horizon Initiative and the Minnesota Long-Term Agricultural Research Network(LTARN)Program.
文摘This study was carried out to analyze the spectral reflectance response of different nitrogen levels for corn crops.Four different nitrogen treatments of 0%,80%,100%and 120%BMP(best management practice)were studied.Principal component analysis-loading(PCA-loading)was used to identify the effective wavelengths.Partial least squares(PLS)and multiple linear regression(MLR)models were built to predict different nitrogen values.Vegetation indices(VIs)were calculated and then used to build more prediction models.Both full and selected wavelengths-based models showed similar prediction trends.The overall PLS model obtained the coefficient of determination(R^(2))of 0.6535 with a root mean square error(RMSE)of 0.2681 in the prediction set.The selected wavelengths for overall MLR model obtained the R^(2) of 0.6735 and RMSE of 0.3457 in the prediction set.The results showed that the wavelengths in visible and near infrared region(350-1000 nm)performed better than the two either spectral regions(1001-1350/1425-1800 nm and 2000-2400 nm).For each data set,the wavelengths around 555 nm and 730 nm were identified to be the most important to predict nitrogen rates.The vogelmann red edge index 2(VOG 2)performed the best among all VIs.It demonstrated that spectral reflectance has the potential to be used for analyzing nitrogen response in corn.
基金supported by the National Key Research and Development Program (2019YFE0125500)University-Locality Integrative Development Project of Yantai (2020XDRHXMPT35)+1 种基金the National Natural Science Foundation of China (31971785 and41801245)the Graduate Training Project of China Agricultural University (JG2019004, JG202026, YW2020007, QYJC202101, and JG202102)。
文摘Estimation of leaf chlorophyll content(LCC) by proximal sensing is an important tool for photosynthesis evaluation in high-throughput phenotyping. The temporal variability of crop biochemical properties and canopy structure across different growth stages has great impacts on wheat LCC estimation, known as growth stage effects. It will result in the heterogeneity of crop canopy at different growth stages, which would mask subtle spectral response of biochemistry variations. This study aims to explore spectral responses on the growth stage effects and establish LCC models suited for different growth stages. A total number of 864 pairwise samples of wheat canopy spectra and LCC values with 216 observations of each stage were sampled at the tillering, jointing, booting and heading stages in 2021. Firstly, statistical analysis of LCC and spectral response presented different distribution traits and typical spectral variations peak at 470, 520 and 680 nm. Correlation analysis between LCC and reflectance showed typical red edge shifts. Secondly, the testing model of partial least square(PLS) established by the entire datasets to validate the predictive performance at each stage yielded poor LCC estimation accuracy. The spectral wavelengths of red edge(RE) and blue edge(BE) shifts and the poor estimation capability motivated us to further explore the growth stage effects by establishing LCC models at respective growth periods.Finally, competitive adaptive reweighted sampling PLS(CARS-PLS), decision tree(DT) and random forest(RF) were used to select sensitive bands and establish LCC models at specific stages. Bayes optimisation was used to tune the hyperparameters of DT and RF regression. The modelling results indicated that CARS-PLS and DT did not extract specific wavelengths that could decrease the influences of growth stage effects. From the RF out-of-bag(OOB) evaluation, the sensitive wavelengths displayed consistent spectral shifts from BE to GP and from RE to RV from tillering to heading stages. Compared with CARS-P
基金Project supported by the National Natural Science Foundation of China(Nos.60776051,60376033)the Beijing Municipal Natural Science Foundation of China(No.4082007)the Beijing Municipal Education Committee of China(Nos.KM200910005001, KM200710005015).
文摘A novel cascaded DFB laser,which consists of two serial gratings to provide selectable wavelengths,is presented and analyzed by the transfer matrix method.In this method,efficient facet reflectivity is derived from the transfer matrix built for each serial section and is then used to simulate the performance of the novel cascaded DFB laser through self-consistently solving the gain equation,the coupled wave equation and the current continuity equations.The simulations prove the feasibility of this kind of wavelength selectable laser and a corresponding designed device with two selectable wavelengths of 1.51μm and 1.53μm is realized by experiments on InP-based multiple quantum well structure.
文摘We numerically study the propagation dynamics of intense optical pulses in gas-filled hollow-core fibers（HCFs）. The spatiotemporal dynamics of the pulses show a transition from tightly confined to loosely confined characteristics as the fiber core is increased, which manifests as a deterioration in the spatiotemporal uniformity of the beam. It is found that using the gas pressure gradient does not enhance the beam quality in large-core HCFs, while inducing a positive chirp in the pulse to lower the peak power can improve the beam quality. This indicates that the self-focusing effect in the HCFs is the main driving force for the propagation dynamics. It also suggests that pulses at longer wavelengths are more suitable for HCFs with large cores because of the lower critical power of self-focusing, which is justified by the numerical simulations. These results will benefit the generation of energetic few-cycle pulses in large-core HCFs.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 90201011 and 10174057）, the Key Project of Chinese Ministry of Education （Grant No 2005-105148） and The 0verseas Scholarship Program of UESTC （University of Electronic Science and Technology of China）.The work was performed at the Imperial College, London. It is a great pleasure to acknowledge the helpful discussions with Dr S. Lucyszyn during the course of this work.
文摘A number of researchers haw reported discrepancies between surface resistance （SR） measurements and classical theoretical predictions in normal metals for millimetre wavelengths （MW）. In this paper, a rigorous model is developed for analysing SR of normal metals. This model is based on quantum mechanical analysis of the spatial dispersion within the metal. We use the model to predict SR and eliminate the discrepancies between SR measurements and classical theoretical predictions in normal metals for MW. Moreover, we have compared the results of this model with that of the classical skin-effect model and classical relaxation-effect model. Our analysis shows that the conductivity is not only frequency- but also wave-vector-dependent for MW. We demonstrate that our model has good quantitative agreement with the published experimental data for the room temperature surface resistance of normal metals for MW.
文摘An extensive theoretical set of atomic data for Rb XXIX in a wide range with L-shell electron excitations to the M-shell has been reported. We have computed energy levels for the lowest 113 fine structure levels of Rb XXIX. The fully relativistic multiconfigurational Dirac-Fock method （MCDF） within the framework of Dirac-Coulomb Hamiltonian taking quantum electrodynamics （QED） and Breit corrections into account has been adopted for calculations. Radiative data are reported for electric dipole （El）, magnetic dipole （MI）, electric quadrupole （E2）, and magnetic quadrupole （M2） transitions from the ground level, although calculations have been performed for a much larger number of levels. To assess the accuracy of results, we performed analogous calculations using flexible atomic code （FAC）. Comparisons are made with existing available results and a good agreement has been achieved. Most of the wavelengths calculated lie in the soft x-ray （SXR） region. Lifetimes for all 113 levels have also been provided for the first time. Additionally, we have provided the spectra for allowed transitions from n = 2 to n = 3 within the x-ray region and also compared our SXR photon wavelengths with experimentally recognized wavelengths. We hope that our results will be beneficial in fusion plasma research and astrophysical applications.
文摘A long-range surface plasmon polariton （LRSPP） waveguide consisting of a 15nm thick gold stripe embedded in a homogeneous polymer BCB is reported. LRSPPs are excited by TM-mode input light successfully using an end-fire method. By scanning the output coupling fibre, the near field of the LRSPP is measured. The propagation loss of as low as 2.34 dB/mm is demonstrated.
