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A femtosecond pulse laser was used to fabricate carbon nanodots (CDs), of which the particle size and photoluminescence (PL) properties could be effectively controlled by adjusting ambient pressure. By increasing the reaction pressure, the particle size of CDs gradually decreased and finally reached less than 1 nm at 4 MPa. Simultaneously, the fluorescence intensity of the CDs first increased and then decreased by further increasing the pressure. By examining the PL dynamics and the chemical structure of the CDs, we found that the PL change of products was attributed to the quantity change of functional groups attached to the CDs due to the surface area change of the carbonic core. [ABSTRACT FROM AUTHOR]

The nonlinear optical response of gold nanoparticles/reduced graphene oxide (AuNPs/rGO) nanocomposites prepared by laser ablation method was studied using a femtosecond laser open-aperture (OA) Z-scan method, and an enhanced nonlinear absorption effect was observed. Using the femtosecond time-resolved pump-probe measurements, the nonlinear response mechanism in the hybrid was studied. When graphene was excited by an ultrashort laser pulse, the bleaching of valence band (VB) and the filling of conduction band (CB) took place, causing a saturable absorption (SA) effect. When decorated with gold nanoparticles, the excited carriers from the CB of graphene could transfer to the sp band of the metal before returning to the VB of graphene. This process would take place in a much longer time scale (∼50 ps) than the direct relaxation in pure graphene, causing the enhancement of the SA effect. The excited carrier dynamics were further demonstrated using femtosecond time-resolved transient absorption spectroscopy, and the interband relaxation of the excited electrons from the sp band of AuNPs to the CB of graphene was observed, resulting in the further filling of the CB of graphene and enhancement of the SA effect. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) nanoparticles (NPs) are synthesized by one-step femtosecond laser ablation of zinc powders in n-methyl pyrrolidone (NMP) at room temperature. The as-prepared ZnO NPs are fairly stable, water-soluble and have abundant surface functional groups resulting in a strong fluorescence in the visible region. By further annealing the ZnO NPs in the reacting solvent up to 120∘C, the photoluminescence (PL) intensity of material can be significantly enhanced. Besides, the PL of ZnO NPs can change from blue to green by controlling the annealing temperature. The products exhibit excellent temperature sensing with high temperature sensitivity and a 1.3% change per ∘C response over a linear temperature sensing range (6–84 ∘ C) in aqueous buffer, which matches well with the physiologically relevant temperatures. Hence, the ZnO nanoparticle system can serve as a promising candidate for practical fluorescent temperatures nanosensors which can be used for accurate temperature monitoring within biological systems. Water-soluble and photoluminescent ZnO NPs are synthesized by femtosecond laser ablation of zinc powders at room temperature. By further annealing, the photoluminescence intensity of the products can be significantly enhanced. The ZnO NPs exhibit excellent temperature sensing with a high sensitivity of 1.3% change per ∘C over a linear range of 6–84∘C in aqueous buffer, which can serve as a promising candidate for fluorescent temperature nanosensors to be used for accurate temperature monitoring within biological systems. [ABSTRACT FROM AUTHOR]

Gold nanorod (GNR) and reduced graphene oxide (rGO) hybrids are synthesized using photochemical method based on femtosecond laser ablation without the usage of strong chemical reducing agents. The products are characterized by absorption spectra, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The formed GNR are well located on the surface of rGO sheets. By adjusting the laser ablation time, the aspect ratio and optical properties of GNR can be well controlled. The produced nanocomposites exhibited an excellent near-infrared (NIR) photothermal performance with a photothermal conversion efficiency of 77.8%, suggesting that the hybrids have large potential as agents in photothermal therapy. • Gold nanorod and graphene hybrids are synthesized using femtosecond laser. • The aspect ratio of gold nanorod can be well controlled by adjusting laser ablation time. • The produced hybrids exhibited an excellent photothermal performance at 808 nm. [ABSTRACT FROM AUTHOR]

Abstract: Liquid-assisted ablation of solids by femtosecond laser pulses has proved to be an efficient tool for highly precise microfabrication, which evokes numerous research interests in recent years. In this paper, we systematically investigate the interaction of femtosecond laser pulses with silicon wafer in water, alcohol, and as a comparison, in air. After producing a series of multiple-shot craters on a silicon wafer in the three types of environments, surface morphologies and femtosecond laser-induced periodic surface structures are comparatively studied via the scanning electron microscope investigations. Meanwhile, the influence of liquid mediums on ablation threshold fluence and ablation depth is also numerically analyzed. The experimental results indicate that the ablation threshold fluences of silicon are reduced by the presence of liquids (water/alcohol) and ablation depths of craters are deepened in ambient water. Furthermore, smoother surfaces tend to be obtained in alcohol-mediated ablation at smaller shot numbers. Finally, the evolution of the femtosecond laser-induced periodic surface structures in air, water and alcohol is also discussed. [Copyright &y& Elsevier]