Shutong Wang

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.

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.

Simulations of Temperature in Disk-Type Laser With Fluid–Solid Interaction

Temperature field in high average power disk-type laser is investigated with fluid-solid interaction (FSI). The coolant flow, heat diffusion, heat convection, and heat conduction in the pumping and cooling processes are analyzed without the arbitrary values of thermal boundary conditions, including boundary temperature, heat flux, or heat exchange coefficient at the cooling faces, which are in turn the simulation results. The velocity field and temperature field of coolant are explored as well as the temperature field of gain medium. Moreover, the influences of coolant flow velocity, deposited heat power and gain medium thickness on temperature field are discussed. Experimental results reveal that simulation of temperature in gain medium with the FSI can get a more accurate temperature filed.

Direct emission of chirality controllable femtosecond LG01 vortex beam

Direct emission of a chirality controllable ultrafast LG01 mode vortex optical beam from a conventional z-type cavity design SESAM (SEmiconductor Saturable Absorber Mirror) mode locked LD pumped Yb:Phosphate laser has been demonstrated. A clean 360 fs vortex beam of ∼45.7 mW output power has been achieved. A radial shear interferometer has been built to determine the phase singularity and the wavefront helicity of the ultrafast output laser. Theoretically, it is found that the LG01 vortex beam is obtained via the combination effect of diagonal HG10 mode generation by off-axis pumping and the controllable Gouy phase difference between HG10 and HG01 modes in the sagittal and tangential planes. The chirality of the LG01 mode can be manipulated by the pump position to the original point of the laser cavity optical axis.Direct emission of a chirality controllable ultrafast LG01 mode vortex optical beam from a conventional z-type cavity design SESAM (SEmiconductor Saturable Absorber Mirror) mode locked LD pumped Yb:Phosphate laser has been demonstrated. A clean 360 fs vortex beam of ∼45.7 mW output power has been achieved. A radial shear interferometer has been built to determine the phase singularity and the wavefront helicity of the ultrafast output laser. Theoretically, it is found that the LG01 vortex beam is obtained via the combination effect of diagonal HG10 mode generation by off-axis pumping and the controllable Gouy phase difference between HG10 and HG01 modes in the sagittal and tangential planes. The chirality of the LG01 mode can be manipulated by the pump position to the original point of the laser cavity optical axis.

Fabrication of microhole arrays on coated silica sheet using femtosecond laser

Abstract. A femtosecond (fs) laser beam machining method has been proposed to improve the quality of micromachining. At first, the coated silica sheet is prepared by pulsed laser deposition, then the coated silica is processed by the fs laser. After that, the aluminum film on a fused silica sheet is cleared out by hydrochloric acid (HCl) in a solution of 10%, and then the microhole array is formed on the silica which has better morphologies. Additionally, some mathematical models are constructed to analyze the diffusion of vapors and reflection of shock waves during the machining process. The theoretical results show that the aluminum film can effectively decrease the pressure gradient of the vapors and the reflection of shock wave pressure on the fused silica during the machining process. The simulation is consistent with experimental results. Finally, coating with a film or not has a great influence on the quality of micromachining, but the types of coating films have little influence. In a word, it is an excellent choice to improve the quality of fs laser processing by coating with a film on a fused silica sheet.

Fabrication and Photocatalytic Properties of ZnSe Nanorod Films

ZnSe nanorod films grown on fused quartz glass substrates via a simple two-step synthesis protocol were demonstrated to be environmentally safe and effective recyclable photocatalysts. These films showed greatly enhanced photocatalytic activity compared to pulsed laser deposition ZnSe films in the degradation of methyl orange dye solutions. The well-crystalized ZnSe nanorods had a length of 15 µm and a diameter of 200 nm and were densely grown on the substrate. The morphology, crystal structure, crystal phase, and photophysical properties of the ZnSe nanorod films were investigated using field-emission scanning electron microscopy (FE-SEM), UV-Vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM).

The effect of the size of Au nanorods on random laser action in a disordered media of ethylene glycol doped with Rh6G dye

Random laser actions in a disordered media based on ethylene glycol doped with Rh6G dye and Au nanorods have been demonstrated. It was observed that the size of Au nanorods strongly affects the pump threshold. The experiment results suggesting that the random lasing properties are dominated by the surface plasmons.

Random lasing in Cr:ZnS microstructure-textured grooves

We report a random lasing emission based on microstructure-textured grooves of Cr:ZnS crystal. The microstructures include horizontal ripples and a vertical periodic structure with dozens of micrometers of periods, which are induced by the Fresnel diffraction of femtosecond laser in the grooves and the interference of laser light through the micropores, respectively. The microstructures multiple-scatter the light, resulting in lasing emission with a center wavelength of 2250 nm and a relatively low lasing threshold of ~80 μJ/pulse. There is a dramatic shortening of the emission lifetime as the pump energy increases. The emission peaks are shifted by pumping at the microstructures with different vertical periods. It shows a structural stable property for potential random laser applications.

The shape effect of Au particles on random laser action in disordered media of Rh6G dye doped with PMMA polymer

Abstract Random laser actions in a disordered media based on polymethyl methacrylate (PMMA) polymer doped with Rh6G dye and Au nanoparticles have been demonstrated. It was observed that the shape of Au nanoparticles can tune the spectral central position of the random laser action. It was also seen that the shape of Au nanoparticles strongly affects the pump threshold. Comparing nanosphere- and nanorod-based systems, the nanorod-based one exhibited a lower threshold.