Second harmonic generation from ZnO films and nanostructures.

Zinc oxide ZnO is a n-type semiconductor having a wide direct band gap (3.37 eV) as well as a non-centrosymmetric crystal structure resulting from hexagonal wurtzite phase. Its wide transparency range along with its second order nonlinear optical properties make it a promising material for efficient second harmonic generation processes and nonlinear optical applications in general. In this review, we present an extensive analysis of second harmonic generation from ZnO films and nanostructures. The literature survey on ZnO films will include some significant features affecting second harmonic generation efficiency, as crystalline structure, film thickness, surface contributes, and doping. In a different section, the most prominent challenges in harmonic generation from ZnO nanostructures are discussed, including ZnO nanowires, nanorods, and nanocrystals, to name a few. Similarly, the most relevant works regarding third harmonic generation from ZnO films and nanostructures are separately addressed. Finally, the conclusion part summarizes the current standing of published values for the nonlinear optical coefficients and for ZnO films and nanostructures, respectively

Optimization of thermochromic VO2 based structures with tunable thermal emissivity

In this paper, we design and simulate VO2/metal multilayers to obtain a large tunability of the thermal emissivity of infrared (IR) filters in the typical mid wave IR window of many infrared cameras. The multilayer structure is optimized to realise a low emissivity filter at high temperatures useful for military purposes. The values of tunability found for VO2/metal multilayers are larger than the value for a single thick layer of VO2. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4739489

Detection of second-order nonlinear optical magnetization by mapping normalized Stokes parameters

A measurable magnetic (nonlocal) contribution to the second harmonic generation (SHG) of nonmagnetic materials is an intriguing issue related to chiral materials, such as biomolecules. Here we report the detection of an intensity-dependent optically induced magnetization of a chiral bacteriorhodopsin film under femtosecond pulse excitation (830 nm) and far from the material's resonance. The analysis of the pump intensity-dependent noncollinear SHG signal, by means of the polarization map of normalized Stokes parameters, allows one to improve the detection of the nonlinear optical magnetization M (2 omega) contribution to the SHG signal. (c) 2013 Optical Society of Americ

Fundamentals of picosecond laser ultrasonics.

The aim of this article is to provide an introduction to picosecond laser ultrasonics, a means by which gigahertz-terahertz ultrasonic waves can be generated and detected by ultrashort light pulses. This method can be used to characterize materials with nanometer spatial resolution. With reference to key experiments, we first review the theoretical background for normal-incidence optical detection in opaque single-layer isotropic thin films. The theory is extended to handle isotropic multilayer samples, and again compared to experiment. We then review applications to anisotropic samples, including oblique-incidence optical probing, and treat the generation and detection of shear waves. Solids including metals and semiconductors are mainly discussed, although liquids are briefly mentioned. © 2014 Elsevier B.V. All rights reserved

Optimization of highly circularly polarized thermal radiation in α\alpha-MoO3_3/β\beta-Ga2_2O3_3 twisted layers

We investigate a bi-layer scheme for circularly polarized infrared thermal radiation. Our approach takes advantage of the strong anisotropy of low-symmetry materials such as $\beta$-Ga$_2$O$_3$ and $\alpha$-MoO$_3$. We numerically report narrow-band, high degree of circular polarization (over 0.85), thermal radiation at two typical emission frequencies related to the excitation of $\beta$-Ga$_2$O$_3$ optical phonons. Optimization of the degree of circular polarization is achieved by a proper relative tilt of the crystal axes between the two layers. Our simple but effective scheme could set the basis for a new class of lithography-free thermal sources for IR bio-sensing.Comment: 11 pages, 6 figure

Midinfrared thermal emission properties of finite arrays of gold dipole nanoantennas

We studied the far-field thermal emission properties of finite arrays of resonant gold dipole nanoantennas at equilibrium temperature. We numerically investigated the transition from the super-Planckian emission of the single resonant antenna to the sub-Planckian emission inherent to infinite periodic arrays. Increasing the number of unit cells of the array, the overall size of the system increases, and the relative emissivity quickly converges to values lower than the unity. Nevertheless, if the separation between nanoantennas in the array is small compared to the wavelength, the near-field interaction makes the emission of each unit cell multipolar. This opens the doors for additional tailoring of the emitted power and directionality of thermal radiation