Guiqiu Wang

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.

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.

Ultrafast responses of dipolar and V-shaped dipicolinate derivatives with potential applications in the labeling of biomolecules

A dipolar dipicolinate derivative, trans-dimethyl-4-[4′-(N,N-diphenylamino)-styry1]-pyridin-2,6-dicarboxylate (P-1), and a P-1based V-shaped compound, {4-[(E)-2-(2,6-dimethoxycarbonylpyridin-4-yl) vinyl]}-N-phenyl-N-{4-[(E)-2-(2,6-dimethoxycarbonylpyridin-4-yl)vinylphenyl]}aniline (P-2), with intense two-photon fluorescence emission properties were systematically investigated by using steady-state absorption and fluorescence spectroscopy, open-aperture Z-scans, and two-photon excited fluorescence (TPF). The two-photon absorption cross-section of the V-shaped compound P-2 in tetrahydrofuran (THF) was determined to be 208 GM, which represents a 6.5-fold enhancement compared with its dipolar counterpart P-1 (32 GM). Extension of the intramolecular charge transfer (ICT) in the V-shaped dipicolinate derivative has been suggested as the mechanism of enhancement. The excited state dynamics from transient absorption spectroscopy were analyzed and discussed. The formation and relaxation lifetimes of the ICT state ...

Ultrafast dynamics of a series multi-branched styryl derivatives with reverse conjugated structural configuration

To study the effect of conjugated structural configurations on the two-photon absorption properties, tri-branched compounds with the same electron-donating and electron-accepting groups connected in a reverse conjugated structural mode, are systematically investigated using steady-state and transient absorption spectroscopies, open-aperture Z-scan, and two-photon fluorescence measurements. The two-photon absorption cross-section of compound R03 with the strong electron donor triphenylamine as the central core of 766 GM is notably large and is approximately 1.7 times larger than that of the tri-branched compound T03-a with a reverse conjugated structural mode and with the 1,3,5-triazine electron acceptor as the central core. This finding indicates that the conjugated mode does have an important effect on the nonlinear optical properties. A two-color pump-probe experiment is used to investigate the ultrafast responses and intra-molecular charge transfer properties of these multi-branched compounds. The form...

Nonlinear optical property and ultrafast response of a two-photon photopolymerization initiator based on dibenzothiophene

A dibenzothiophene-based two-photon photopolymerization (TPP) initiator named E,E-1,4-bis[3-vinyl-dibenzothiophene]-2,5-dimethoxybenzene (VBPMOB) with intense two-photon fluorescence (TPF) was investigated by UV–visible, fluorescence, pump–probe and time-resolved fluorescence spectroscopies. The maximum two-photon absorption (TPA) cross-section of VBPMOB in DMF was determined to be 274GM. In addition, the TPA cross-section at 800nm was 230GM, which is the most commonly used wavelength for TPP. The ultrafast spectra result indicated that after excitation, the VBPMOB molecule will first undergo a fast internal conversion process to form an intramolecular charge transfer (ICT) state with a certain width followed by relaxation of the ICT state with fluorescence emission.