Liangen Ding

Ultraviolet luminescence enhancement of ZnO two-dimensional periodic nanostructures fabricated by the interference of three femtosecond laser beams

We have developed a simple and rapid method for fabricating ZnO periodic nanostructures. By changing the laser polarization combinations, we fabricated different types of two-dimensional (2D) nanostructures on ZnO crystal surfaces by the interference of three femtosecond laser beams. The 2D nanostructures became more regular and uniform when increasing the cross angles between any two laser beams. Compared with the case of the plane surfaces of ZnO crystals, the 2D nanostructures revealed an ultraviolet (UV) luminescence enhancement excited by an 800 nm femtosecond laser beam. We studied the photoluminescence properties of the 2D nanostructures and the mechanisms of the UV luminescence enhancement. Our results indicated that the enhancement was caused by an increase in optical absorption with respect to that of the unaltered ZnO plane surface and by the formation of surface defect states.

Optical limiting response in a unsymmetrical dithiolene metal complex (Me4N)2[Zn(dmit)(Sph)2]

Abstract We report the measurements of reverse saturable absorption (RSA) and optical limiting responses in a unsymmetric dithiolene metal complex (Me 4 N) 2 [Zn(dmit)(Sph) 2 ] with nanosecond and picosecond laser pulses at 532 nm. The experimental results show that the triplet–triplet absorption is responsible for the measured RSA, resulting in optical limiting responses. The measured data can be well simulated by a rate equation model to obtain the absorption cross-section of the excited state.

Resonant third-order optical nonlinearity of a new subphthalocyanine

Abstract We have investigated the resonant third-order nonlinear optical properties of a new subphthalocyanine (bromoboron trineopentyloxy-subphthalocyanine) using picosecond degenerate four-wave mixing. The measured χpure(3) was 6.9×10 −10 esu . The second hyperpolarizability 〈γ〉 value is 3.0×10 −31 esu . The response time of χ(3) was determined to be less than the resolution of optical pulse duration (

π-electron density dependence of third-order optical nonlinearities in poly(1,4-phenylene vinylene) derivatives

The third-order nonlinear optical properties of poly(1,4-phenylene vinylene) (PPV), poly(2-bromo-1,4-phenylene vinylene) (BrPPV) and poly(2-chloro-1,4-phenylene vinylene) (ClPPV) were studied by forward degenerate four-wave mixing (DFWM). They have large and ultrafast third-order optical nonlinear responses, which mainly arise from the distortion of the large π-conjugated electronic charge distribution in the backbone. It was found that there was a significant contribution to π-electron density and thus χ(3) values from the substituents at the phenylene ring.

Nanosecond reverse saturable absorption and optical limiting in (Me 4 N) 2 [Cd(dmit)(Sph) 2 ]

We report the measurement of reverse saturable absorption and an optical limiting response in a new metallorganic material, (Me4N)2[Cd(dmit)(Sph)2], with nanosecond laser pulses at 532 nm. Pump–probe and open-aperture Z-scan techniques were used as mechanisms for an optical limiting response. The experimental results show that triplet–triplet absorption is responsible for measurable reverse saturable absorption at 532 nm, which results in optical limiting. The measured data can be simulated well by a rate-equation model, and thus the absorption cross section of the excited state can be evaluated.

Background-free third-order harmonic generation induced by dynamic gratings in dual filaments

Background-free third-order harmonic generation is observed from dynamic gratings induced by dual laser filaments in argon gas. The filaments were generated by focusing two intense 60 fs laser pulses noncollinearly into a gas cell. The optimal result is achieved with gas pressure of 2 atm and zero relative delay. It seems that the off-axis third-harmonic generation is mainly due to the interaction between the two interfering fundamental pulses and their filaments.

Collision-induced destructive quantum interference

We conduct theoretical studies on the collision-induced destructive quantum interference of two-colour two-photon transitions in an open rhomb-type five-level system with a widely separated doublet by the density matrix approach. The effects of the collision-induced decay rates, the ratio of the transition dipole moments and the energy separation of the doublet on the interference are analysed. It is shown that a narrow dip appears in the excitation spectrum due to the collision-induced destructive interference, and that the narrow interference dip still exists even when the collision broadening is comparable to the energy separation of the doublet. The physical origin of the collision-induced destructive quantum interference is analysed in the dressed-atom picture.

Lineshape variations of two-photon transitions based on quantum interference in Na2

We report the lineshape variations of two-photon transitions in a rhomb-type four-level system in sodium dimer. A straightforward explanation is given by performing theoretical analysis and calculation.

Third-order optical nonlinearities for lanthanum (III) complexes with 1, 10-phenanthroline components

The nonlinear refractive indexesn2 for the ethanol solutions of 1, 10-phenanthroline (2.0 × 10−3 mol · L−1), [bis(l, 10-phenanthroline) lanthanum (III)] nitrate (1.0 × 10−3 mol · L−1), and [nitrato-fluoracil-bis (1, 10-phenanthroline) lanthanum (III) ] nitrate (1.0 × 10−3 mol · L−1) are first measured, the third-order nonlinear optical susceptibilities χ(3) and 〈γ〉 are calculated, and the mechanisms of the third-order optical nonlinearities enhanced by lanthanum (III) are discussed preliminarily.

New process for generating broadly tunable UV coherent radiation: two-step hybrid resonance four-wave mixing in molecule-atom system

Tunable UV coherent radiation in the wavelength region 319.2 nm to approximately 354.2 nm has been generated by unequal-frequency hybrid resonance of Na2-Na system and followed four-wave mixing. The wave-mixing processes and experimental results are discussed.