Reconstruction of absorption coefficient μa and scattering coefficient μs is very important for applications of diffuse optical tomography and near infrared spectroscopy. Aiming at the early cancer detection of cerv...Reconstruction of absorption coefficient μa and scattering coefficient μs is very important for applications of diffuse optical tomography and near infrared spectroscopy. Aiming at the early cancer detection of cervix and stomach, we present a fast inverse Monte-Carlo scheme for extracting μa and μs of a tubular tissue from the measurement on frequency domain. Results show that the computation time for reconstructing one set of μa and μs is less than 1 min and the relative errors in reconstruction are less than ±10% for the optical properties of normal cervical tissue and precancerous lesions.展开更多
A self-organized thin film of a cyanine dye is fabricated by the spin-coating technique and is characterized by ultraviolet-visible spectroscopy, infrared （IR） spectroscopy, small-angle X-ray diffraction, eUipsomete...A self-organized thin film of a cyanine dye is fabricated by the spin-coating technique and is characterized by ultraviolet-visible spectroscopy, infrared （IR） spectroscopy, small-angle X-ray diffraction, eUipsometer, and atomic force microscopy （AFM）. The nonlinear optical properties of the thin films are investigated by degenerate four wave mixing （DFWM） technique. The cyanine dye thin film sample exhibits high optical nonlinearities （χ^（3） = 2.55 × 10^-12 esu）, and the mechanism is analyzed by the exciton coupling theory.展开更多
We performed detailed temperature-dependent optical measurements on optimally doped Ba0.6K0.4Fe2As2 single crystal, We examine the changes of the in-plane optical conductivity spectral weight in the normal state and t...We performed detailed temperature-dependent optical measurements on optimally doped Ba0.6K0.4Fe2As2 single crystal, We examine the changes of the in-plane optical conductivity spectral weight in the normal state and the evolution of the superconducting condensate in the superconducting state. In the normal state, the low-frequency spectral weight shows a metallic response with an arctan （T） dependence, indicating a T-linear scattering rate behavior for the carriers. A high energy spectral weight transfer associated with the Hund＇s coupling occurs from the low frequencies below 4000 cm^-1 5000 cm^-1 to higher frequencies up to at least 104 cm^-1. Its temperature dependence analysis suggests that the Hund＇s coupling strength is continuously enhanced as the temperature is reduced. In the superconducting state, the FGT sum rule is conserved according to the spectral weight estimation within the conduction bands, only about 40% of the conduction bands participates in the superconducting condensate indicating that Ba0.6K0.4Fe2As2 is in dirty limit.展开更多
The far-infrared optical reflectivity of an optimaUy doped Ba1-xKxFe2As2 （x = 0.4） single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active ph...The far-infrared optical reflectivity of an optimaUy doped Ba1-xKxFe2As2 （x = 0.4） single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 em-1. This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continu- ously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observa- tions indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping in the optimally doped Bao.6Ko.4Fe2As2 compound.展开更多
The upconversion properties of Er^3＋-doped heavy metal oxyfluoride germanate glasses under 975 nm excitation have been investigated. The intense green （551 and 529 nm） and relatively weak red （657 nm） emissions c...The upconversion properties of Er^3＋-doped heavy metal oxyfluoride germanate glasses under 975 nm excitation have been investigated. The intense green （551 and 529 nm） and relatively weak red （657 nm） emissions corresponding to the transitions ^4S3/2→^4I15/2, ^2H11/2→^4 I15/2 and ^4F9/2 →^4I15/2, respectively, were simultaneously observed at room temperature. The content of PbF2 has an important influence on the upconversion luminescence emission. With increasing content of PbF2, the intensities of green （529 nm） and red （657 nm） emissions increase slightly, while the green emission （551 nm） increases markedly. These results suggest that PbF2 has an influence on the green （551 nm） emission more than on the green （529 nm） and red （657 nm） emissions.展开更多
Pr3+and Yb3+co-doped phosphate glasses are prepared to study their optical properties.Excitation and emission spectra and decay curves are used to characterize their luminescence.We demonstrate that upon excitation of...Pr3+and Yb3+co-doped phosphate glasses are prepared to study their optical properties.Excitation and emission spectra and decay curves are used to characterize their luminescence.We demonstrate that upon excitation of Pr3+ion with one high energy photon at 470 nm,two near-infrared(NIR)photons are emitted at 950-1100 nm(Yb3+:2F 5/2 →2F 7/2)through an efficient cooperative energy transfer(CET)from Pr3+to Yb3+.The maximum energy transfer efficiency(ETE)and the corresponding quantum efficiency approach up to 90.17%and 190.17%,respectively.The glass materials might find potential application for improving the efficiency of silicon-based solar cells.展开更多
Thin films of amorphous diamond like carbon (a:DLC) were deposited by using a novel technique. By electrodeposition from methanol-camphor solution thin a:DLC films were deposited on non-conductive glass substrates and...Thin films of amorphous diamond like carbon (a:DLC) were deposited by using a novel technique. By electrodeposition from methanol-camphor solution thin a:DLC films were deposited on non-conductive glass substrates and also on high resistive Si substrates, by using a fine wire mesh electrode, at atmospheric pressure and temperature below 350 K. Thin films of a:DLC were doped by incorporation of nitrogen (a:N-DLC) and boron (a:B-DLC) using urea and boric acid with methanol-camphor solution respectively during the electrodeposition process. From transmittance measurements in the UV-VIS-NIR region, the optical energy band gap of about 1.0 eV for undoped a:DLC film, 2.12 eV for a:N-DLC and 2.0 eV for a:B-DLC films were determined. The spectra showed high transparency in the visible and NIR region. Fourier transform infrared spectroscopy (FTIR) measurements showed the appearance of various C-H and C-C bonding in the spectrum of undoped amorphous DLC film and confirmed C-N and C=N bond formation in a:N-DLC film. From the temperature variation of d.c. conductivity studies, the activation energies were determined and found to be 0.75 eV, 0.32 eV and 0.58 eV for undoped a:DLC films, a:N-DLC and a:B-DLC films respectively. Electrical resistivity at room temperature was reduced by the doping effect, from 109 Ω-cm for undoped films to 107 Ω-cm for nitrogen doped films and 108 Ω-cm for boron doped films.展开更多
To reveal the intrinsic properties of the basic superconducting units,i.e.,the single layered FeSe/FeAs in iron-based superconductors or CuO_(2) planes in cuprate superconductors,is a necessary prerequisite for unders...To reveal the intrinsic properties of the basic superconducting units,i.e.,the single layered FeSe/FeAs in iron-based superconductors or CuO_(2) planes in cuprate superconductors,is a necessary prerequisite for understanding the mechanism of high-Tc superconductivity.Up to now,an isolated FeAs layer has rarely been studied due to the difficulty in materials synthesis.Here,we report a scanning tunneling microscopy/spectroscopy(STM/STS)study on the iron-based superconductor KCa_(2)Fe_(4)As_(4)F_(2).In situ cleavage produced a single FeAs layer covered by a reconstructed K surface,which is isolated from the bulk by the underlying CaF layer and shows multi-band superconductivity with a much lower T_(c) than its bulk counterpart.In the exposed As-terminated regions with coverage of scattered K atoms,a pseudogap was observed,leading to an inhomogeneous superconductivity without long-range phase coherence in real space,which is remarkably similar to the high-T_(c) cuprate superconductors.These results provide a new perspective to understanding the origin of superconductivity in iron-based superconductors.展开更多
基金supported by the National Natural Science Foundation of China(No.60578008 and 60678089)the National Basic Research Program of China(No.2006CB705700)
文摘Reconstruction of absorption coefficient μa and scattering coefficient μs is very important for applications of diffuse optical tomography and near infrared spectroscopy. Aiming at the early cancer detection of cervix and stomach, we present a fast inverse Monte-Carlo scheme for extracting μa and μs of a tubular tissue from the measurement on frequency domain. Results show that the computation time for reconstructing one set of μa and μs is less than 1 min and the relative errors in reconstruction are less than ±10% for the optical properties of normal cervical tissue and precancerous lesions.
基金This work was supported by the National Natural Science Foundation of China(No.10574046)the National Key Project for Basic Research of China(No.2006CB806006 and 2006CB921105)+4 种基金the Program for Changjiang Scholars and Innovative Research Team in University(PCSIRT)the Program for New Century Excellent Talents in University(NCET-04-0420)the Doctoral Program of High Education(No.20050269011)the Phosphor Program sponsored by Shanghai Science Technology Committee(No. 06QH14003)the Twilight Project sponsored by Shanghai Education Committee(No.03SG23).
文摘A self-organized thin film of a cyanine dye is fabricated by the spin-coating technique and is characterized by ultraviolet-visible spectroscopy, infrared （IR） spectroscopy, small-angle X-ray diffraction, eUipsometer, and atomic force microscopy （AFM）. The nonlinear optical properties of the thin films are investigated by degenerate four wave mixing （DFWM） technique. The cyanine dye thin film sample exhibits high optical nonlinearities （χ^（3） = 2.55 × 10^-12 esu）, and the mechanism is analyzed by the exciton coupling theory.
基金Project supported by the National Basic Research Program of China(Grant Nos.2012CB821403,2011CBA00107,and 2012CB921302)the National Natural Science Foundation of China(Grant Nos.11374345,11104335,and 91121004)
文摘We performed detailed temperature-dependent optical measurements on optimally doped Ba0.6K0.4Fe2As2 single crystal, We examine the changes of the in-plane optical conductivity spectral weight in the normal state and the evolution of the superconducting condensate in the superconducting state. In the normal state, the low-frequency spectral weight shows a metallic response with an arctan （T） dependence, indicating a T-linear scattering rate behavior for the carriers. A high energy spectral weight transfer associated with the Hund＇s coupling occurs from the low frequencies below 4000 cm^-1 5000 cm^-1 to higher frequencies up to at least 104 cm^-1. Its temperature dependence analysis suggests that the Hund＇s coupling strength is continuously enhanced as the temperature is reduced. In the superconducting state, the FGT sum rule is conserved according to the spectral weight estimation within the conduction bands, only about 40% of the conduction bands participates in the superconducting condensate indicating that Ba0.6K0.4Fe2As2 is in dirty limit.
基金Project supported by the National Natural Science Foundation of China （Grant Nos. 11104335 and 91121004）, the National Basic Research Program of China （Grant Nos. 2011CBA00107, 2012CB821400, and 2009CB929102）, and the ANR, France （Grant No. BLAN07-1-183876 GAPSUPRA）.
文摘The far-infrared optical reflectivity of an optimaUy doped Ba1-xKxFe2As2 （x = 0.4） single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 em-1. This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continu- ously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observa- tions indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping in the optimally doped Bao.6Ko.4Fe2As2 compound.
基金Project supported by the National Natural Science Foundation of China （Grant No 60207006）.
文摘The upconversion properties of Er^3＋-doped heavy metal oxyfluoride germanate glasses under 975 nm excitation have been investigated. The intense green （551 and 529 nm） and relatively weak red （657 nm） emissions corresponding to the transitions ^4S3/2→^4I15/2, ^2H11/2→^4 I15/2 and ^4F9/2 →^4I15/2, respectively, were simultaneously observed at room temperature. The content of PbF2 has an important influence on the upconversion luminescence emission. With increasing content of PbF2, the intensities of green （529 nm） and red （657 nm） emissions increase slightly, while the green emission （551 nm） increases markedly. These results suggest that PbF2 has an influence on the green （551 nm） emission more than on the green （529 nm） and red （657 nm） emissions.
基金supported by the National Natural Science Foundation of China(Nos.61275180,51272109and50972061)the Natural Science Foundation of Zhejiang Province(Nos.Z4110072and R4100364)+1 种基金the Opening Foundation of Zhejiang Provincial Top Key DisciplineK.C.Wong Magna Fund in Ningbo University
文摘Pr3+and Yb3+co-doped phosphate glasses are prepared to study their optical properties.Excitation and emission spectra and decay curves are used to characterize their luminescence.We demonstrate that upon excitation of Pr3+ion with one high energy photon at 470 nm,two near-infrared(NIR)photons are emitted at 950-1100 nm(Yb3+:2F 5/2 →2F 7/2)through an efficient cooperative energy transfer(CET)from Pr3+to Yb3+.The maximum energy transfer efficiency(ETE)and the corresponding quantum efficiency approach up to 90.17%and 190.17%,respectively.The glass materials might find potential application for improving the efficiency of silicon-based solar cells.
文摘Thin films of amorphous diamond like carbon (a:DLC) were deposited by using a novel technique. By electrodeposition from methanol-camphor solution thin a:DLC films were deposited on non-conductive glass substrates and also on high resistive Si substrates, by using a fine wire mesh electrode, at atmospheric pressure and temperature below 350 K. Thin films of a:DLC were doped by incorporation of nitrogen (a:N-DLC) and boron (a:B-DLC) using urea and boric acid with methanol-camphor solution respectively during the electrodeposition process. From transmittance measurements in the UV-VIS-NIR region, the optical energy band gap of about 1.0 eV for undoped a:DLC film, 2.12 eV for a:N-DLC and 2.0 eV for a:B-DLC films were determined. The spectra showed high transparency in the visible and NIR region. Fourier transform infrared spectroscopy (FTIR) measurements showed the appearance of various C-H and C-C bonding in the spectrum of undoped amorphous DLC film and confirmed C-N and C=N bond formation in a:N-DLC film. From the temperature variation of d.c. conductivity studies, the activation energies were determined and found to be 0.75 eV, 0.32 eV and 0.58 eV for undoped a:DLC films, a:N-DLC and a:B-DLC films respectively. Electrical resistivity at room temperature was reduced by the doping effect, from 109 Ω-cm for undoped films to 107 Ω-cm for nitrogen doped films and 108 Ω-cm for boron doped films.
基金supported by the National Key Research and Development Program of China(Grant Nos.2018YFA0305602,2022YFA1403203,and 2017YFA0303201)the National Natural Science Foundation of China(Grant Nos.12074002,92265104,12022413,11674331,and 12104004)+2 种基金the“Strategic Priority Research Program(B)”of the Chinese Academy of Sciences(Grant No.XDB33030100)the Major Basic Program of Natural Science Foundation of Shandong Province(Grant No.ZR2021ZD01)supported by the High Magnetic Field Laboratory of Anhui Province,China。
文摘To reveal the intrinsic properties of the basic superconducting units,i.e.,the single layered FeSe/FeAs in iron-based superconductors or CuO_(2) planes in cuprate superconductors,is a necessary prerequisite for understanding the mechanism of high-Tc superconductivity.Up to now,an isolated FeAs layer has rarely been studied due to the difficulty in materials synthesis.Here,we report a scanning tunneling microscopy/spectroscopy(STM/STS)study on the iron-based superconductor KCa_(2)Fe_(4)As_(4)F_(2).In situ cleavage produced a single FeAs layer covered by a reconstructed K surface,which is isolated from the bulk by the underlying CaF layer and shows multi-band superconductivity with a much lower T_(c) than its bulk counterpart.In the exposed As-terminated regions with coverage of scattered K atoms,a pseudogap was observed,leading to an inhomogeneous superconductivity without long-range phase coherence in real space,which is remarkably similar to the high-T_(c) cuprate superconductors.These results provide a new perspective to understanding the origin of superconductivity in iron-based superconductors.
