We present a new fabrication method, called ‘‘vertical spin coating,’’ to prepare highly oriented J aggregates dispersed in polymer films. Linear dichroic spectra of the oriented J aggregate of 1,1′-diethyl-2,2′-quinocyanine bromide PIC-Br were measured at 5 K. The dichroic ratio at the peak of J band was 5 to 10, dependent on the preparation conditions. Precise measurement of the dichroism at the J band revealed that the J band is composed of two bands with transition dipole moments perpendicular to each other. The films are stable even at room temperature, and have applications as nonlinear optical devices.
A high-power continuous-wave polycrystalline 1% Nd:Y3Al5O12 (Nd:YAG) ceramic rod laser was demonstrated. With 290 W/808 nm laser diode pumping, cw laser output of 72 W was obtained at 1064 nm. The optical-to-optical conversion efficiency is 24.8%. Thermally induced birefringence properties of Nd:YAG ceramic was also investigated.
Exciton migration dynamics in a dendritic molecule: Quantum master equation approach using ab initio molecular orbital configuration interaction method Ultrafast exciton dynamics of J-aggregates in room temperature solution studied by third-order nonlinear optical spectroscopy and numerical simulation based on exciton theoryWe observed the ultrafast response of exciton (S 1 -exciton͒ and excited-exciton (S 2 -exciton͒ in one-dimensional J-aggregates of three-level porphyrin molecules by femtosecond pump-probe spectroscopy. The decay profiles of the nonlinear response can be fitted to a sum of instantaneous response and two exponential decay components with time constants of 1.3Ϯ0.1 and 40Ϯ1 ps. The former and latter were found to correspond to the lifetimes of S 2 -and S 1 -excitons, respectively. The origins of the nonlinearity were attributed to the following three contributions: ͑1͒ coherent effects between the pump and probe via one-photon virtual S 1 -exciton, ͑2͒ induced absorption of real S 2 -excitons generated by two photons, and ͑3͒ induced absorption of real S 1 -exciton.
Time-resolved X-ray absorption spectroscopy was performed for aqueous ammonium iron(III) oxalate trihydrate solutions using an X-ray free electron laser and a synchronized ultraviolet laser. The spectral and time resolutions of the experiment were 1.3 eV and 200 fs, respectively. A femtosecond 268 nm pulse was employed to excite [Fe(III)(C2O4)3]3− in solution from the high-spin ground electronic state to ligand-to-metal charge transfer state(s), and the subsequent dynamics were studied by observing the time-evolution of the X-ray absorption spectrum near the Fe K-edge. Upon 268 nm photoexcitation, the Fe K-edge underwent a red-shift by more than 4 eV within 140 fs; however, the magnitude of the redshift subsequently diminished within 3 ps. The Fe K-edge of the photoproduct remained lower in energy than that of [Fe(III)(C2O4)3]3−. The observed red-shift of the Fe K-edge and the spectral feature of the product indicate that Fe(III) is upon excitation immediately photoreduced to Fe(II), followed by ligand dissociation from Fe(II). Based on a comparison of the X-ray absorption spectra with density functional theory calculations, we propose that the dissociation proceeds in two steps, forming first [(CO2•)Fe(II)(C2O4)2]3− and subsequently [Fe(II)(C2O4)2]2−.
We have developed a method of dispersive x-ray absorption spectroscopy with a hard x-ray free electron laser (XFEL), generated by a self-amplified spontaneous emission (SASE) mechanism. A transmission grating was utilized for splitting SASE-XFEL light, which has a relatively large bandwidth (ΔE/E ∼ 5 × 10−3), into several branches. Two primary split beams were introduced into a dispersive spectrometer for measuring signal and reference spectra simultaneously. After normalization, we obtained a Zn K-edge absorption spectrum with a photon-energy range of 210 eV, which is in excellent agreement with that measured by a conventional wavelength-scanning method. From the analysis of the difference spectra, the noise ratio was evaluated to be ∼3 × 10−3, which is sufficiently small to trace minute changes in transient spectra induced by an ultrafast optical laser. This scheme enables us to perform single-shot, high-accuracy x-ray absorption spectroscopy with femtosecond time resolution.
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