Yaochuan Wang

Star-Shaped Donor-π-Acceptor Conjugated Oligomers with 1,3,5-Triazine Cores: Convergent Synthesis and Multifunctional Properties

Monodispersed oligomers have been widely developed and used in different optoelectronic areas due to their well-defined molecular structures, high purity, and solution processability. Star-shaped oligomers are especially interesting for OLED application because of their antiaggregation abilities and stable electroluminescence. In addition, star-shaped donor-pi-acceptor conjugated molecules are known to afford good nonlinear optical and two-photon absorption properties due to the intramolecular charge transfer and cooperative enhancement effects. In this context, three generations of highly soluble 1,3,5-triazine based donor-pi-acceptor compounds, TFT1, TFT2, and TFT3, were prepared through a convergent synthetic strategy and their optoelectronic properties were fully studied, which showed distinct correlations with the structures. Closed-aperture and open-aperture Z-scan methods were employed to measure the nonlinear refractive index and two-photon absorption properties of the oligomers, respectively. TFT1 showed a high nonlinear refractive index of 4.14 x 10(-12) esu in THF solution with an excitation wavelength of 800 nm. Also, TFT1 exhibited a large two-photon absorption cross section of 234 GM and a frequency up-converted two-photon excited fluorescence with a lambda(TPEF)(max) value of 527 nm under 800 nm laser irradiation with a pulse duration of 140 fs. OLED devices using the spin-coated films of these oligomers as an active layer showed intensive blue electroluminescence with a maximum luminance of 3093 cd/m(2) at a current efficiency of 1.47 cd/A from TFT1.

Evolution properties of partially coherent flat-topped vortex hollow beam in oceanic turbulence

Employing the theory of coherence, the partially coherent flat-topped vortex hollow beam is first introduced. The analytical propagation equation for a partially coherent flat-topped vortex hollow beam in oceanic turbulence is derived by using the extended Huygens-Fresnel diffraction integral and the spectrum of oceanic turbulence. The influences of coherence length, beam order N, the topological charge M, and the parameters of oceanic turbulence on evolution properties of partially coherent flat-topped vortex hollow beams propagating in oceanic turbulence are obtained by using the numerical examples.

Probing ultrafast excited state dynamics and nonlinear absorption properties of three star-shaped conjugated oligomers with 1,3,5-triazine core

The effects of different bridging fluorene units on the two-photon absorption (TPA) properties and ultrafast response of organic conjugated oligomers were investigated for three star-shaped oligomers named TFT-1, TFT-2 and TFT-3. These three oligomers are composed of the same central core 1,3,5-triazine, with three arms that consist of specific numbers of bridging fluorene groups and with triphenylamine as electron-donating group at the terminal end of each arm. The studies on these oligomers were carried out by using two-photon excited fluorescence (TPF), degenerate pump–probe techniques, transient absorption spectroscopy and time-resolved photoluminescence (TRPL) methods. The TPA cross-sections were determined to be 1509 GM, 1260 GM and 789 GM for TFT-1, TFT-2 and TFT-3, respectively, decreasing with the increase of bridging fluorene number. Ultrafast dynamics results show that there is a fast intramolecular charge transfer (ICT) formation time of about several ps and a relatively long decay process of the ICT state. The formation time of ICT was found to increase from TFT-1 (1.9 ps), to TFT-2 (3.0 ps) and TFT-3 (6.3 ps), with the increased number of the fluorene bridge, which may explain the action of fluorene bridge on the electron transmission properties, the ICT properties and the TPA behavior.

Evolution properties of partially coherent four-petal Gaussian vortex beams propagating in uniaxial crystals orthogonal to the optical axis.

The analytical propagation equations for partially coherent four-petal Gaussian vortex beams propagating through uniaxial crystals orthogonal to the optical axis are derived, and the propagation properties are analyzed by numerical examples. The influence of beam order n, topological charge M, the coherence length, and the ratio of refractive index n(e)/n(o) on the normalized intensity distribution of partially coherent four-petal Gaussian vortex beams is discussed.

Propagation properties of partially coherent four-petal Gaussian vortex beams in oceanic turbulence

Based on the extended Huygens–Fresnel principle, the analytical expressions for partially coherent four-petal Gaussian vortex beams propagating in oceanic turbulence are obtained, and the influence of the coherence length, beam order N, topological charge M and oceanic turbulence parameters on the evolution properties of beams are discussed in detail using numerical examples. The results show that the beam will evolve into a Gauss-like beam rapidly with decreasing coherence length and oceanic parameters and , or increasing oceanic parameter in the far field due to the influence of the coherence length and oceanic turbulence.

Evolution properties of partially coherent four-petal Gaussian beams in oceanic turbulence

Abstract Based on the extended Huygens–Fresnel integral formula, the analytical expressions for partially coherent four-petal Gaussian beam propagating in oceanic turbulence are derived, and the influences of coherence length, beam order N and the parameters of oceanic turbulence (the rate of dissipation of turbulent kinetic energy per unit mass of fluid, the rate of dissipation of mean square temperature and the relative strength of temperature and salinity fluctuations) on average intensity properties are investigated using numerical examples in detail. The results show that the beam with the higher beam order N or coherence length will lose its initial four-petal profiles slower. It is also indicated that the beam will evolve into a Gauss-like beam more rapidly with increasing oceanic turbulence strength. The results have the potential application in underwater laser communication using a partially coherent four-petal Gaussian beam.

Propagation Properties of a Partially Coherent Flat-Topped Vortex Hollow Beam in Turbulent Atmosphere

Using coherence theory, the partially coherent flat-topped vortex hollow beam is introduced. The analytical equation for propagation of a partially coherent flat-topped vortex hollow beam in turbulent atmosphere is derived, using the extended Huygens-Fresnel diffraction integral formula. The influence of coherence length, beam order N, topological charge M, and structure constant of the turbulent atmosphere on the average intensity of this beam propagating in turbulent atmosphere are analyzed using numerical examples.

Propagation properties of a partially coherent Lorentz beam in uniaxial crystal orthogonal to the optical axis

The cross-spectral density function of a partially coherent Lorentz beam propagating in uniaxial crystal orthogonal to the optical axis is obtained, and the evolution properties and the spectral degree of coherence for a partially coherent Lorentz beam in uniaxial crystal are illustrated by using numerical examples. The influence of coherence length and the ratio of refractive index ne/no on the normalized intensity and spectral degree of coherence for a partially coherent Lorentz beam are analyzed in detail.

Propagation of partially coherent Lorentz–Gauss vortex beam through oceanic turbulence

The partially coherent Lorentz-Gauss vortex beam generated by a Schell-model source has been introduced. Based on the extended Huygens-Fresnel principle, the cross-spectral density function of a partially coherent Lorentz-Gauss vortex beam propagating in oceanic turbulence is derived. The influences of coherence length, topological charge M, and oceanic turbulence on the spreading properties and position of the coherence vortex for a partially coherent Lorentz-Gauss vortex beam are analyzed in detail. The results show that a partially coherent Lorentz-Gauss vortex beam propagating in stronger oceanic turbulence will evolve into a Gaussian-like beam more rapidly as the propagation distance increases, and the number of coherent vortices will change.

Evolution Properties of a Partially Coherent Flat-topped Vortex Hollow Beam Propagating in Uniaxial Crystals Orthogonal to the Optical Axis

The analytical expressions for a partially coherent flat-topped vortex hollow beam propagating in uniaxial crystals orthogonal to the optical axis are derived, and the intensity and coherent vortex properties of partially coherent flat-topped vortex hollow beam propagation in uniaxial crystals orthogonal to the optical axis are analyzed by numerical examples. The influence of beam order parameter N, topological charge M, the coherence length and the ratio of refractive indices ne/no of uniaxial crystals on the normalized intensity distribution and coherent vortex of a partially coherent flat-topped vortex hollow beam propagating in uniaxial crystals are discussed in detail.