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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]

Phase-matched second-harmonic generation (SHG) in thermal-cross-linking polyurethane films was demonstrated using a thermal-assisted nonresonant optical poling technique. During the seeding process, samples heated in an oven were irradiated simultaneously by coherent superposition of the 1300 nm fundamental and 650 nm second-harmonic lights of a femtosecond laser. The photoinduced second-order optical nonlinearity of the polymer films seeded at elevated temperatures kept stable at room temperature. The measurements for the dependence of SHG on the film thickness showed that a χ(2) grating that satisfied the phase-matching condition for SHG was optically induced in the polymer films. [ABSTRACT FROM AUTHOR]

An ultrafast optical Kerr gate of Bi2O3–B2O3–SiO2 oxide glass (BI glass) was used in an ultrafast time-resolved imaging system for shape measurement of objects. The experimental results showed that the longitudinal resolution of the imaging system using the ultrafast optical Kerr gate was less than 20 μm and the measurements of object shape using the ultrafast optical Kerr gate of BI glass had more advantages compared with that using CS2. [ABSTRACT FROM AUTHOR]

The influence of the size parameter of the scatterers on ultrafast optical Kerr gate (OKG) imaging is investigated in highly scattering poly-disperse turbid media. The results show that in a poly-disperse turbid medium, which in our case, is a suspension of two different sized mono-disperse microspheres, the temporal and spatial behaviors of the light pulses transmitted through it are dominated by the smaller microspheres. The contrasts of the OKG images for the poly-disperse microsphere sample are closer to the contrasts of the OKG images for the smaller sized mono-disperse microsphere sample. [ABSTRACT FROM PUBLISHER]

Abstract: Fabrication of three-dimensional microfluidic channels in glasses by water-assisted ablation with femtosecond laser pulses was investigated. The experimental results showed that formation of the photoinduced microchannels by femtosecond pulses depended on the incident laser power and the scanning speed. For the same scanning speed, the shape of cross-section of channels changed from ellipse to circle with increasing the laser power. Under the optimum condition of laser processing, we fabricated two layers of microfluidic channels with diameter of about 8μm inside glass. The distance between two layers of microchannels was about 20μm. [Copyright &y& Elsevier]

We have developed an ultrafast time-resolved imaging technique for the propagation dynamics of ultrashort laser pulses in transparent media. This method utilizes the optical polarigraphy technique and a chirped supercontinuum as the probe light. The supercontinuum senses the instantaneous birefringence induced by the propagation of an intense pulse, and a polarigraphy image with different color distributions could be obtained. Using this method, we performed a space-time characterization of the filament induced by a femtosecond laser pulse in CS2, indicating that this technique could be used for the single-shot imaging of pulse propagation dynamics. [ABSTRACT FROM AUTHOR]

Abstract: Femtosecond lasers have proved to be effective tools for micromachining silicon carbide material. In the drilling process, however, when the debris around the hole was not removed efficiently, the depth of hole would not increase further. In this paper, alcohol-assisted photoetching of 6H silicon carbide was investigated using a femtosecond laser. Machining in the presence of alcohol was beneficial to the debris ejection from the hole. The alcohol flow and volatilization was also helpful to further carry away the ablation debris and reduce the ablated material redeposition. The experiment showed that photoetching assisted by alcohol produced cleaner ablation effect and deeper hole than in ambient air. Moreover, alcohol assistance would not produce additional thermal damage around the hole. Vias were formed in a 250μm thick wafer with alcohol-assisted photoetching technique using a femtosecond laser, which demonstrated the potential for this processing technique. [Copyright &y& Elsevier]

We demonstrate a novel scheme based on active mode locking combined with four-wave mixing (FWM) to generate ultra-short pulse trains at high repetition rate with multiple wavelengths for applications in various fields. The obtained six wavelengths display high uniformity both in temporal and frequency domain. Pulses at each wavelength are mode locked with pulse duration of ~44.37 ps, signal-to-noise ratio (SNR) of ~47.89 dB, root-mean-square (RMS) timing jitter of ~552.7 fs, and the time-bandwidth product of ~0.68 at repetition rate of 1 GHz. The experimental results show this scheme has promising usage in optical communications, optical networks, and fiber sensing. [ABSTRACT FROM AUTHOR]

Diode-pumped pulsed Er-doped ZBLAN fiber lasers at 2.8 μm actively Q-switched by using an mechanical Q-switch with feedbacks of a protected gold mirror and a blazing grating were investigated, respectively. A pulse energy of 0.13 mJ and repetition rate of 10 kHz with a pulse width of 127.3 ns at 2.78 μm was obtained when using a protected gold mirror as the feedback. By replacing the mirror with a blazing grating in Littrow configuration, the wavelength of the Q-switched pulse train was tunable with over 100 nm tuning range from 2.71 to 2.82 μm and a linewidth of ~1.5 nm. A maxinmum pulse energy of up to 0.15 mJ and repetition rate of 10 kHz with a pulse width of 92.6 ns was achieved, yielding the maximum peak power of exceeding 1.6 kW. The pulse energy and peak power, to our knowledge, are the highest ever reported in the mid-infrared Q-switched fiber lasers. [ABSTRACT FROM AUTHOR]

Abstract: We fabricated spherical microlenses on optical glasses by femtosecond laser direct writing (FLDW) in ambient air. To achieve good appearances of the microlenses, a meridian-arcs scanning method was used after a selective multilayer removal process with spiral scanning paths. A positive spherical microlens with diameter of 48μm and height of 13.2μm was fabricated on the surface of the glass substrate. The optical performances of the microlens were also tested. Compared to the conventional laser direct writing (LDW) technique, this work could provide an effective method for precise shape-controlled fabrication of three-dimensional (3D) microstructures with curved surfaces on difficult-to-cut materials for practical applications. [Copyright &y& Elsevier]

Abstract: We encoded surface relief micro-gratings on Au–Cr thin films using two-beam interference of femtosecond laser pulses with the durations from 25fs to 70fs. The dependence of the fabrication quality on the pulse duration has been investigated both numerically and experimentally. The results revealed that the shorter pulses were preferable to prepare periodical microstructures with minimal ablation fringe width and satisfied fabrication quality. This work has potential applications on periodic functional microstructures fabrication for ultra-fine processing and modification on various materials, especially for intractable materials. [Copyright &y& Elsevier]