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The spaser (a plasmonic nanolaser) has rapidly advanced as a subwavelength light source candidate. Herein, we introduce a spaser based on a quantum-dot, mesoporous-oxide, and metal structure from top to bottom consisting of CdS/ZnS core/shell quantum dots, a mesoporous silica film (MSF), and an Au film, respectively. Two-photon pumping using femtosecond laser pulses at 800 nm creates amplified spontaneous emission at approximately 451 nm. The advantages of MSF as a dielectric gap layer are examined through numerical simulations. Measuring the dependence of the luminescence intensity on the average pump power confirms the occurrence of two-photon up-conversion luminescence. [ABSTRACT FROM AUTHOR]

With a microscopic imaging system composed of microscopic objective, lens and CCD, we observe the complicated structures in the speckle fields on the surface of a rough screen. It is found that such structures contain ridge stripes, large platform-like grains, and shivy grains, exhibiting multiple scales in size and multiple fractalities. Simulations shows these structures are formed by different parts of the rough surface. The experimental curve of the autocorrelation function of the speckle intensity includes the three parts of the central peak, the transition part and the long tail part. Using the sum of self-affine fractal models with different scales and fractalities, we propose theoretically a triple-scale autocorrelation function to describe the speckle field. Fit of this autocorrelation function to the experimental curve gives the values of such parameters as average speckle sizes and fractalities in different scales of the speckle structures. [ABSTRACT FROM AUTHOR]

We study the optical properties of light scattering by a monocrystalline silicon wafer, by using transparent material to replicate its surface structure and illuminating a fabricated sample with a laser source. The experimental results show that the scattering field contains four spots of concentrated intensity with high local energy, and these spots are distributed at the four vertices of a square with lines of intensity linking adjacent spots. After discussing simulations of and theory about the formation of this light scattering, we conclude that the scattering field is formed by the effects of both geometrical optics and physical optics. Moreover, we calculate the central angle of the spots in the light field, and the result indicates that the locally-enhanced intensity spots have a definite scattering angle. These results may possibly provide a method for improving energy efficiency within mono-Si based solar cells. [ABSTRACT FROM AUTHOR]

We report a heptad vortex array structure in the wave fields in an extremely deep Fresnel diffraction region by asymmetrical subwavelength holes in a metal film illuminated with linearly polarized light. A Mach–Zehnder interferometer with a microscopic objective is used to record the wave fields at different distances, and the phase maps are extracted by Fourier transform of the interference intensities. We study the evolutions of the heptad vortex array with distance from the sample to the object plane. To explain the formations and the evolutions of the vortex array, we calculate the diffracted wave fields with Kirchhoff's diffraction theory. The calculations are basically consistent with the experimental results, and the properties of the heptad vortex array structure are reasonably explained. [ABSTRACT FROM AUTHOR]

We analyze the distribution properties of phase and phase vortices in a speckle field generated by N-pinhole random screens, and find that the phase vortex distributions show similarity and clustering in local regions. The phase patterns have a lot of sets composed of two phase vortices with opposite signs or four phase vortices which are positive and negative vortices alternately. Cases are also found where two adjacent phase vortices have the same topological charges. The density of phase vortices becomes larger with the increase of the radius of circumference and the number of pinholes on screen. Then, the relative positions of phase vortices can be adjusted by changing the radius of circumference and the number of pinholes. [ABSTRACT FROM AUTHOR]