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61.
全无机无铅卤化物钙钛矿已经成为重要的新一代太阳能电池材料.采用密度泛函理论的第一性原理研究了不同静水压下CsSnX3(X=I, Br, Cl)材料的晶体结构,电子结构和光学性能,并分析了其内在联系.结果表明施加静水压可使材料中Sn-X键长减小,使原子之间的耦合增强,带隙值减小,且随着卤族元素半径的增大,压力效应越明显;随着压力的增加,材料的吸收系数和复折射率增大,吸收光谱出现红移现象,在可见光区和近红外光区吸收增强.相比CsSnBr3和CsSnCl3,CsSnI3在可见光区吸收最佳且受压力作用影响最小,更适用于钙钛矿太阳能电池材料. 相似文献
62.
Anisotropic (elliptically polarized) photoinduced second harmonic generation (PISHG) in SiNxOy/Si1 1 1 films was proposed for contact-less monitoring of specimens with different nitrogen to oxygen (N/O) ratios. As a source for the photoinducing light, we used a nitrogen Q-switched pulse laser at wavelengths of 315, 337 and 354 nm as well as doubled frequency YAG–Nd laser wavelength (λ=530 nm). The YAG : Nd pulse laser (λ=1.06 μm; W=30 MW; τ=10–50 ps) was used to measure the PISHG. All measurements were done in a reflected light regime. We found that the output PISHG signal was sensitive to the N/O ratio and the film thickness. Measurements of the PISHG versus pumping wavelengths, powers, incident angles as well as independent measurements of the DC-electric field induced second harmonic generation indicate the major role played in this process by axially symmetric photoexcited electron–phonon states. The SiNxOy films were synthesized using a technique of chemical evaporation at low pressures. Films with thickness varying between 10 and 30 nm and with an N/O ratio between 0 and 1 were obtained. Electrostatic potential distribution at the Si1 1 1–SiNxOy interfaces was calculated. Comparison of the experimentally obtained and quantum chemically calculated PISHG data are presented. High sensitivity of anisotropic PISHG to the N/O ratio and film thickness is revealed. The role of the electron–phonon interactions in the dependencies observed is discussed. We have shown that the PISHG method has higher sensitivity than the traditional extended X-ray absorption fine structure spectroscopic and linear optical method for films with the N/O ratio higher than 0.50. 相似文献
63.
64.
H. Pu T. Cai N.P. Bigelow 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):269-278
We present a semi-classical theory of the light pressure force for atoms interacting with a two-dimensional laser field. Unlike
previous 2D theory, ours is valid for general atomic level and laser field configurations. We show that striking new features
appear in the velocity-dependent force arising from the multi-dimensionality. Finally, we describe in detail the novel numerical
technique used in the calculation.
Received 4 December 1998 and Received in final form 13 February 1999 相似文献
65.
We have analyzed the optical properties of a-Ge30-xSbxS70 chalcogenide glass films (x=0,10,20 and 30 at%); the chalcogenide films were prepared by vacuum thermal evaporation. The optical-absorption data indicate that the absorption mechanism is non-direct transition. We found that the optical band gap, Eopt, decreases from 2.04±0.01 to 1.74±0.01 eV, whereas the refractive index increases with increasing Sb content. Data are analyzed by the Wemple equation, which is based on the single-oscillator model. 相似文献
66.
The increasing use of low power cw lasers in various applications calls for the design of optical limiters with low thresholds. To this end, the optical nonlinearity exhibited by zinc tetraphenyl porphyrin at low laser powers is utilized to design an optical limiter for low threshold operation. The basic parameter responsible for limiting action, the nonlinear refractive index of the medium, is measured using the Z-scan technique and found to have a value of at the helium–neon laser wavelength of 632.8 nm. The origin of nonlinearity is explained on the basis of the thermal lens model. It is shown that effective optical limiting at desired threshold values can be achieved by the optimal choice of aperture size and experimental geometry. 相似文献
67.
L. Besombes Y. Lger L. Maingault D. Ferrand J. Cibert H. Mariette 《Physica E: Low-dimensional Systems and Nanostructures》2006,35(2):300
The magnetic state of a single magnetic ion (Mn2+) embedded in an individual quantum dot is optically probed using micro-spectroscopy. The fine structure of a confined exciton in the exchange field of a single Mn2+ ion (S=) is analyzed in detail. The exciton–Mn2+ exchange interaction shifts the energy of the exciton depending on the Mn2+ spin component and six emission lines are observed at zero magnetic field. The emission spectra of individual quantum dots containing a single magnetic Mn atom differ strongly from dot to dot. The differences are explained by the influence of the system geometry, specifically the in-plane asymmetry of the quantum dot and the position of the Mn atom. Depending on both these parameters, one has different characteristic emission features which either reveal or hide the spin state of the magnetic atom. The observed behavior in both zero field and under magnetic field can be explained quantitatively by the interplay between the exciton–Mn2+ exchange interaction (dependent on the Mn position) and the anisotropic part of the electron–hole exchange interaction (related to the asymmetry of the quantum dot). 相似文献
68.
Filled and unfilled polyvinylalcohol (PVA) films were prepared by the casting technique. Films of equal amounts with various concentrations of two fillers (CoBr2 and MgCl2) were prepared. Spectroscopic, structural and some physical properties of these films were studied with different techniques. Fourier-transform infrared (FTIR) revealed that the syndiotacticity structure of the PVA samples causes dense molecular packing in the crystal and also stronger intermolecular hydrogen bonds, which are responsible for the disappearance of the molecular motion. X-ray diffraction (XRD) scans evidenced the presence of some semicrystalline structure of PVA films. The optical absorption spectra suggested the presence of an optical gap (Eg), which depends on filler concentration for all the filling levels. Differential thermal analysis (DTA) suggests that the segmental mobility of an amorphous pure PVA increases as a result of the addition of mixed fillers, becoming less-rigid segments. This indicates that the mixed fillers act as plasticizers. 相似文献
69.
R. Kheradmand M. Sahrai H. Tajalli G. Tissoni L. A. Lugiato 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(1):107-112
We present here a method for selecting optical patterns in a passive
semiconductor microresonator, by using a spatial perturbation. A pattern is
spontaneously generated in the system, and a switching beam causes this
pattern to rotate even if the power in the switching beam is much lower than
the power in the pattern. Thus, an all optical switch is realized, that
operates at low light levels. 相似文献
70.
Nonlinear wave propagation is studied theoretically in a one-dimensional photonic band gap structure containing single negative materials. It is found that Kerr nonlinearity is greatly enhanced near the lower edge of a recently explored angular gap for transverse magnetic polarized light. Consequently, optical bistability is achieved at very low values of input intensity in a periodic structure composed of only a few repeating units. The characteristics of optical bistability are affected only slightly with the variation of the incident angle and thickness ratio of the layers. The effect of losses is also found to be relatively insignificant in such a small structure. 相似文献