Yinglin Song

A tunable unidirectional surface plasmon polaritons source

A new structure to be used as a tunable unidirectional surface plasmon source is introduced. The structure is composed of two silver films, with a nanoslit fabricated in the top Ag film and lying below is a movable Ag film. The field distribution of the structure is investigated by using the finite-difference time-domain(FDTD) method. It is found that the surface plasmon polariton intensity and the splitting ratio change periodically as the bottom film is moved, which is interpreted in terms of surface plasmon polaritons interference in two Fabry-Perot(F-P) cavities. The period obtained by the FDTD agrees well with the F-P interferometer model. The surface plasmon polaritons can be unidirectionally excited with a large intensity splitting ratio.

Novel [60]fullerene–silver nanocomposite with large optical limiting effect

Abstract A novel [60]fullerene–Ag nanocomposite (DTC 60 –Ag) is prepared by the in situ reduction of silver ions encapsulated in a new mono-functionalized methano-[60]fullerene derivative (DTC 60 ) with reverse micelle-like structure. The formation and size of the nanocomposite has been determined from the UV–Vis plasmon absorption band, FT-IR spectra method and transmission electron microscopic (TEM) analysis. The average size distribution is about 5.2 mm. The optical limiting properties of DTC 60 and DTC 60 –Ag are measured via a nanosecond Nd:YAG pulse laser system at a wavelength of 532 nm. The experimental results demonstrate that the optical limiting behavior of DTC 60 –Ag is better than that of both C 60 and DTC 60 .

Analysis of focal-shift effect in planar metallic nanoslit lenses.

A theoretical analysis based on scalar diffraction theory about the recently reported focal-shift phenomena in planar metallic nanoslit lenses is presented. Under Fresnel approximation, an axial intensity formula is obtained, which is used to analyze the focal performance in the far field zone of lens. The relative focal shift is totally dependent on the Fresnel number only. The influences of the lens size, preset focal length and incident wavelength can be attributed to the change of Fresnel number. The total phase difference of the lens is approximately equal to the Fresnel number multiplied by π. Numerical simulations performed using finite-difference time-domain (FDTD) and near-far field transformation method are in agreement with the theoretical analysis. Using the theoretical formula assisted by simple numerical method, we provide predictions on the focal shift for the previous literatures.

Measurements of the triplet state nonlinearity of C60 in toluene using a Z-scan technique with a nanosecond laser

Triplet state nonlinearity of C60 in toluene is studied using the Z-scan technique with 8 ns, 532 nm pulses from a Q-switched Nd:YAG laser. Compared with the Z-scan results of C60 in toluene and iodine in toluene with proper concentration, the solvent instantaneous nonlinearity and the thermal nonlinearity resulting from the C60 intersystem crossing and excited state absorption are estimated. The real part of the C60 triplet state molecular polarizability is obtained.

Energy gradient architectured praseodymium chalcogenide quantum dot solar cells: towards unidirectionally funneling energy transfer

The energy level alignment of quantum dot solar cells is key to many of the performance characteristics of devices. However, only a few of the quantum dot semiconductor systems have been available thus far, which limits the tunability of both the energy level position and absorption band edge. Here, we present a facile strategy for the first time to prepare a series of praseodymium chalcogenide colloidal quantum dots as alternate light harvesters. By sequentially layering quantum dots, rainbow quadruple-stack junctions with energy gradient architecture are constructed. It is demonstrated that the overall charge transfer time constant from the donor to the acceptor is considerably shortened from 877–1099 to 385 ps, thus leading to a significant enhancement in short-circuit current density (as high as 15.40 mA cm−2) and in power conversion efficiency by over 30% compared to its double-stack counterparts. This work reveals that the formation of the cascade energy level is desirable for robust quantum dot solar cells and concrete evidence has been provided to highlight the role of the energy level in improving photovoltaic performances such as short-circuit current density.

Measurement of the C60 molecular polarizability of the excited singlet state using Z-scan

Abstract We report on a method of determining the C 60 molecular polarizability α e of the excited singlet state under 23 picosecond excitation at 532 nm using the Z -scan technique. Based on the Clausius–Mossotti equation, the sign and the magnitude of the real part and the imaginary part of α e are respectively measured to be 1.2×10 −22 and 7.2×10 −23 esu. We also obtain the nonlinear refractive cross section σ r of 4.2×10 −17 cm 2 .

Method with a phase object for measurement of optical nonlinearities

A new and simple technique is presented to investigate nonlinear optical properties. In this technique, a phase object is introduced into the measurement system. Both the nonlinear absorption coefficient and nonlinear refraction index can be determined conveniently by measuring the transmittance of the sample. The optical nonlinearities of the ZnSe are investigated by using this technique with 19 ps pulses at 532 nm wavelength as a test.

Investigation of the room-temperature solid-state reactions leading to ZnS nanotubes and the third-order nonlinear optical properties of the nanotubes obtained

The room-temperature solid-state reactions occurring in the preparation of nanotubes of zinc sulfide are further investigated by x-ray powder diffractometry (XRD) and infra-red (IR) spectrometry measurements, and the nanotube ZnS product obtained is measured by Z-scan technology to investigate the third-order nonlinear optical (NLO) properties. The XRD result suggests that the reactions leading to the formation of the nanotubules have occurred through reaction-controlled to growth-controlled procedures, and the IR result indicates that the procedures involve a coordination effect of the additive DABCO as ligand on the reactant. The result of NLO measurements shows that the nanotube ZnS products obtained have the behaviours of the third-order nonlinear optical properties of both NLO absorption and NLO refraction with self-focusing effects.

Solute migration caused by excited state absorptions

Using the Z-scan technique, we find that migration of chloroaluminum phthalocyanine in liquid ethanol can be induced by the absorption of a 19 ps laser pulse with energy exceeding a threshold but not by that of a 2.8 ns pulse depositing more energy at the solute molecules. Considering each solute molecule as an oscillator confined within a potential well, we explain, in accordance with the five-energy-band model, that solute molecules excited by a 19 ps pulse retain more translational excess energy to overcome the potential well barrier compared with those excited by a 2.8 ns pulse of equal energy. Therefore, they are more likely to migrate out of the laser beam center, weakening the solutions absorption that we detect in the Z-scan measurements. Furthermore, we theoretically infer that the 19 ps pulse-induced solute migration tends to be nonquasistatic and experimentally verify that it cannot be attributed to the Soret effect, a quasistatic process.

Determination of nonlinear absorption mechanisms using a single pulse width laser

A simple optical setup that uses a single pulse width laser is proposed to identify different kinds of nonlinear optical absorption mechanisms. It can easily distinguish reverse saturable absorption from two photon absorption, and direct three photon absorption from two photon absorption followed by one photon absorption from the excited level. Both theoretical and experimental results are reported.