Achieving high numerical aperture near-infrared imaging based on an ultrathin cylinder dielectric metalens.

An artificial subwavelength dielectric metalens (ML), the realization of being ultrathin and light-weight, provides a potential candidate with replacing a traditional bulky curved lens with a high image quality. A ML with 1.5 mm in diameter having numerical aperture (NA) $\sim{0.60}$∼0.60 at the near-infrared wavelength of $\lambda = 0.94 \,\,{\unicode{x00B5}{\rm m}}$λ=0.94µm was designed by the finite-difference time-domain (FDTD) method with speeding up optimization of the MLs' scheme by the deep neural network (DNN) model. Additionally, an ultrathin high NA ML was achieved by cost effective semiconductor manufacturing technology. The fabricated ML can focus an incident light down to a spot as small as $ \sim{5.2}\,\,{\rm \unicode{x00B5}{\rm m}} $∼5.2µm with high optical efficiency of $\sim{88.4}\% $∼88.4% (focusing efficiency achieved, 23.7%). We also provided an efficient MLs' semiconductor manufacturing technology for the development of an optical device in near-infrared image technology.

Phase retrieval by using the transport-of-intensity equation with Hilbert transform.

Phase recovery by solving the transport-of-intensity equation (TIE) is a non-iterative and non-interferometric phase retrieval technique. From solving the TIE with conventional, one partial derivative and Hilbert transform methods for both the periodic and aperiodic samples, we demonstrate that the Hilbert transform method can provide the smoother phase images with edge enhancement and fine structures. Furthermore, compared with the images measured by optical and atomic force microscopy, the Hilbert transform method has the ability to quantitatively map out the phase images for both the periodic and aperiodic structures.

Raman study of alloy potential fluctuations in Mg(x)Zn(1-x)O nanopowders.

The blueshift of near-band-edge emission and excitonic absorption indicate that Zn(2+) ions are successfully substituted by Mg(2+) ions in Mg(x)Zn(1-x)O nanopowders for 0≤x≤0.14. The changes in Raman spectral linewidth and the asymmetry of the E(2) (high) mode for various Mg contents can be well described by a modified spatial correlation model that considers the grain size distribution. With increasing Mg concentration, the alloy potential fluctuations lead to a decrease in the grain size, which is induced by the surplus Mg(2+) that could form MgO clusters surrounding the crystalline MgZnO.

Enhanced resonant raman scattering and electron-phonon coupling from self-assembled secondary ZnO nanoparticles.

Self-assembled secondary ZnO nanoparticles, recognized with the agglomeration of crystalline subcrystals, are successfully synthesized by a simple sol-gel method. TEM images display that one artificial cluster behaves in a single-crystal-like wurtzite structure because subcrystals coagulate as the same crystal orientation. Moreover, from the resonant Raman scattering, the as-grown sample exhibits phonon red shift; meanwhile, the coupling strength between electron and longitudinal optical phonon, determined by the ratio of second- to first-order Raman scattering cross sections, diminishes compared with the samples after postannealing at 350 and 500 degrees C. The size dependence of electron-phonon coupling is principally as a result of the Fröhlich interaction.