The femtosecond transient absorption (TA) characterization of a new benzothiadiazole (BT)-based donor-acceptor conjugated copolymer, poly[(2,6-dithieno[3,2-b:2',3'-d]thiophene)-alt-(4,7-di(4-octyldodecylthiopen-2-yl)-2,1,3-benzo[c][1,2,5]thiadiazole (PBT), as well as its fluorinated derivatives, PFBT and PDFBT, is carried out. Additionally, bulk heterojunction (BHJ) films consisting of the copolymers and [6,6]-phenyl-C71 -butylic acid methyl ester (PC70 BM) are examined using TA spectroscopy. Both the singlet excited state dynamics in the copolymers and the charge transfer state dynamics in the BHJs are investigated in terms of fluorination dependency; the fluorinated copolymers exhibit less singlet exciton recombination rate than the fluorine-free copolymer, and the BHJs including the fluorinated copolymers display slower monomolecular recombination than the fluorine-free analogue. Furthermore, the excitation-intensity-dependent TA dynamics of the copolymers and BHJs is investigated, revealing that, when sufficiently high excitation intensity is used to induce annihilation processes, the fluorinated copolymers and BHJs incorporating the fluorinated copolymers show more rapid TA decay ascribable to morphological enhancement. These TA spectroscopic findings are found to correlate with the device characteristics with respect to fluorinated content in the polymer solar cells. In particular, both the short-circuit current density and fill factor of BHJ solar cells correspond closely with the fast decay parameters of the BHJ films under high excitation intensity.
A comparative analysis on five edible oils with the same chemical composition but different composition ratios was performed by using coherent anti‐Stokes Raman scattering spectroscopy in the wavenumber 2400–3200 cm−1 corresponding to C─H vibration band. Intensity ratio (I═C ─ H/IC ─ H) in C─H stretching region was obtained according to the mixing ratio of the two types of edible oil, and the fitting curves were obtained from the fact that the intensity ratio is proportional to the square of
N═normalC─normalHtrue/NnormalC─normalH where
Nk is the expectation value of k bonds of the edible oil.
N═normalC─normalH and
NnormalC─normalH of the edible oils obtained from the fitting curves were well matched with the referred values. And finally, we showed that the coherent anti‐Stokes Raman scattering spectroscopy can be used as a method of authentication of adulterated edible oil by demonstrating a method to determine the type and the amount of unknown mixed oil.
Photoemission measurements with barium and single crystal LaB6 photocathodes are reported. The barium cathode is prepared by depositing a barium thin film onto a copper substrate. The LaB6 cathode is a single crystal cut in the 〈100〉 plane. Radiation from a nitrogen laser (337 nm, 10 ns) is polarized and strikes the cathode surface at variable angles. An electron quantum yield as high as 2×10−3 is observed with barium. The dependence of the quantum yield on the beam polarization and angle of incidence is investigated. The results indicate that higher quantum yields are achieved when the angles of polarization and incidence are such as to minimize the reflection coefficient.
We report on the development of a compact, gas-filled capillary plasma source for plasma accelerator applications. The one-body sapphire capillary was created through a diamond machining technique, which enabled a straightforward and efficient manufacturing process. The effectiveness of the capillary as a plasma acceleration source was investigated through laser wakefield acceleration experiments with a helium-filled gas cell, resulting in the production of stable electron beams of 200 MeV. Discharge capillary plasma was generated using a pulsed, high-voltage system for potential use as an active plasma lens. A peak current of 140 A, corresponding to a focusing gradient of 97 T/m, was observed at a voltage of 10 kV. These results demonstrate the potential utility of the developed capillary plasma source in plasma accelerator research using electron beams from a photocathode gun.
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