Shouhuan Zhou

Nanocrystalline Cr2+-doped ZnSe Nanowires Laser

By using femtosecond laser pulses to ablate microsized targets that are dispersed in liquid media, nanocrystalline Cr(2+)-doped ZnSe nanowires have been successfully fabricated for the first time. The phase and stoichiometries of the original materials are preserved while the sizes are reduced down to 30-120 nm for these nanowires. X-ray diffraction results show that the products are nanocrystalline ZnSe with cubic sphalerite structure. Scanning electron microscope results indicate that the products be ZnSe nanowires. The nanowires are usually 30-120 nm in diameter and several tens of micrometers in length. Photoluminescence of the nanocrystalline Cr(2+)-doped ZnSe nanowires shows strong emission at around 2000-2500 nm under excitation of 1300-2250 nm wavelength at room temperature. By using the Cr(2+)-doped ZnSe multiple nanowires as the gain medium, mid-infrared oscillation at 2194 nm has been established. The oscillation wavelength of the multiple nanowires laser is 150 nm shifted to shorter wavelengths in comparison with that of microsized powder random laser.

Spatial carrier phase-shifting algorithm based on principal component analysis method

A non-iterative spatial phase-shifting algorithm based on principal component analysis (PCA) is proposed to directly extract the phase from only a single spatial carrier interferogram. Firstly, we compose a set of phase-shifted fringe patterns from the original spatial carrier interferogram shifting by one pixel their starting position. Secondly, two uncorrelated quadrature signals that correspond to the first and second principal components are extracted from the phase-shifted interferograms by the PCA algorithm. Then, the modulating phase is calculated from the arctangent function of the two quadrature signals. Meanwhile, the main factors that may influence the performance of the proposed method are analyzed and discussed, such as the level of random noise, the carrier-frequency values and the angle of carrier-frequency of fringe pattern. Numerical simulations and experiments are given to demonstrate the performance of the proposed method and the results show that the proposed method is fast, effectively and accurate. The proposed method can be used to on-line detection fields of dynamic or moving objects.

Enhanced four-wave mixing in graphene-silicon slow-light photonic crystal waveguides

We demonstrate the enhanced four-wave mixing of monolayer graphene on slow-light silicon photonic crystal waveguides. 200-μm interaction length, a four-wave mixing conversion efficiency of −23 dB is achieved in the graphene-silicon slow-light hybrid, with an enhanced 3-dB conversion bandwidth of about 17 nm. Our measurements match well with nonlinear coupled-mode theory simulations based on the measured waveguide dispersion, and provide an effective way for all-optical signal processing in chip-scale integrated optics.

Effective random laser action in Rhodamine 6G solution with Al nanoparticles

We have studied the random laser action in Rhodamine 6G (Rh6G) ethylene glycol solution with Al nanoparticles. The experiment results are obtained by pumping with a nanosecond (7 ns) laser pulse, which demonstrated the existence of effective random laser emission. It is found that the threshold of the random laser depends on the concentration of the Rh6G and the concentration of Al nanoparticles. The concentration and diameter of Al nanoparticles have effects on the optical path; a higher concentration or a larger diameter results in a shorter optical path length. Also multimode survival and mode competition have been observed at a relatively high concentration (0.08 M) of Rh6G, where the concentration of Al nanoparticles is 0.0015 M.

Coherent random lasing from liquid waveguide gain channels with biological scatters

A unidirectional coherent random laser based on liquid waveguide gain channels with biological scatters is demonstrated. The optical feedback of the random laser is provided by both light scattering and waveguide confinement. This waveguide-scattering-feedback scheme not only reduces the pump threshold but also makes the output of random laser directional. The threshold of our random laser is about 11 μJ. The emission spectra can be sensitively tuned by changing pump position due to the micro/nano-scale randomness of butterfly wings. It shows the potential applications of optofluidic random lasers for bio-chemical sensors on-chip.

Circular common-path point diffraction interferometer

A simple and compact point-diffraction interferometer with circular common-path geometry configuration is developed. The interferometer is constructed by a beam-splitter, two reflection mirrors, and a telescope system composed by two lenses. The signal and reference waves travel along the same path. Furthermore, an opaque mask containing a reference pinhole and a test object holder or test window is positioned in the common focal plane of the telescope system. The object wave is divided into two beams that take opposite paths along the interferometer. The reference wave is filtered by the reference pinhole, while the signal wave is transmitted through the object holder. The reference and signal waves are combined again in the beam-splitter and their interference is imaged in the CCD. The new design is compact, vibration insensitive, and suitable for the measurement of moving objects or dynamic processes.

Microsized structures assisted nanostructure formation on ZnSe wafer by femtosecond laser irradiation

Micro/nano patterning of ZnSe wafer is demonstrated by femtosecond laser irradiation through a diffracting pinhole. The irradiation results obtained at fluences above the ablation threshold are characterized by scanning electron microscopy. The microsized structure with low spatial frequency has a good agreement with Fresnel diffraction theory. Laser induced periodic surface structures and laser-induced periodic curvelet surface structures with high spatial frequency have been found on the surfaces of microsized structures, such as spikes and valleys. We interpret its formation in terms of the interference between the reflected laser field on the surface of the valley and the incident laser pulse.

Temperature dependence of laser-induced micro/nanostructures for femtosecond laser irradiation of silicon

The temperature dependence (from 25°C to 350°C) of laser-induced micro/nanostructures for multiple linearly polarized femtosecond laser pulse (pulse duration τ=35  fs, wavelength λ=800  nm) irradiation of silicon in air is studied experimentally. Distinct micro/nanostructures are fabricated at elevated temperature. Low spatial frequency, laser-induced periodic ripple structures (LSFL), which are perpendicular to the polarization of the laser beam, are formed at all temperatures. Micrometer-size grooves, which are oriented perpendicular to the LSFL ripples, have been observed in the central part of the irradiated area above 150°C. The threshold to fabricate the LSFL ripples goes from 1.65 to 2  kJ/m2 while the temperature of the substrate increases from 25°C to 350°C. The possible mechanism of the temperature dependence of the micro/nanostructure generation is also discussed. These results demonstrate that temperature is an important parameter to be tuned to tailor the micro/nanostructure fabrication.

A Compact and Stable Temperature Sensor Based on a Gourd-Shaped Microfiber

A compact and stable temperature sensor based on a gourd-shaped microfiber is fabricated and experimentally demonstrated. Claddings of the two microspheric structured fibers, which constitute the gourd shape, are spliced together but their cores are not. The transmission spectrum of the sensor features interference fringe due to the cavity formed inside the gourd-shaped microfiber. Increasing temperatures results in a significant red shift of fringe dip wavelength with a slope of

Enhanced photoresponsivity in graphene-silicon slow-light photonic crystal waveguides

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