arXiv subjects

Hernando Garcia

Publications and source records attributed to Hernando Garcia.

7 recordsLinked to original sources

arXiv2019

Construction of a Compact, Fully Automatic non-linear Absorption Spectrometer to Measure the Two-Photon Absorption Coefficient

Using an Electrically Focus Tunable Lens (EFTL), an integrating sphere and a tunable femtosecond-pulse laser (Mai Tai HP), we were able to measure the degenerate two-photon absorption coefficient (in transmission) of CdS and ZnSe in a long range of wavelengths (690-1040 nm), with a 5 nm resolution, in less than 30 minutes. We compared our results with theoretical approaches for the dispersion relations of the non-linear properties of semiconductors, and found excellent agreement with the experimental results. The system has no moving parts, is highly compact, and is fully automated.

physics.ins-det↗

arXiv2018

Single-beam reflection technique for determination of nonlinear-refractive index of thin-film semiconductors using an electrically focus tunable lens

In this paper, we propose a technique named reflection F-scan or RF-scan, that can be used to measure the nonlinear-refractive index n_2 of thin-film semiconductors. In this technique, a p-polarized Gaussian beam is focused using an electrically focus-tunable lens onto a sample, which is positioned at a fixed distance from the lens and makes an angle with respect to the optical axis. Due to EFTL has the capability to vary its focal distance over a specific range when an electric current is applied to it. The electrically focus-tunable lens varies its focal distance as a function of an applied electric current over a specific range thus, when light is focused on the surface of the sample the beam intensity is high enough to generate nonlinear optical effects such as changes in the refractive index of the material. This changes are then register as variations in reflectance, measured by an intensity detector. Results for three-dimensional CH3NH3PbBr3 hybrid perovskite thin films are presented.

physics.optics↗

arXiv2018

Two-photon absorption coefficient determination with a differential F-scan technique

In this paper we present a modification to the recently proposed transmission F-scan technique, the differential F-scan technique. In differential F-scan technique the programmed focal distance in the electronic-tunable lens oscillates, allowing the light detector of the setup to record a signal proportional to the derivative of the signal recorded with an F-scan. As for the differential Z-scan a background-free signal is obtained, but also the optical setup is simplified and the available laser power is double. We also present and validate a new fitting-procedure protocol that increments the accuracy of the technique. Finally, we show that fitting a signal from differential F-scan or the derivate of the signal of transmission F-scan is more accurate than simply fitting the signal from F-scan directly. Results from two-photon absorption at 790 nm of CdS, ZeSe and CdSe are presented.

physics.app-ph↗

arXiv2007

In silico design of metal-dielectric nanocomposites for solar energy applications

Recently, a homogenization procedure has been proposed, based on the tight lower bounds of the Bergman-Milton formulation, and successfully applied to dilute ternary nanocomposites to predict optical data without using any fitting parameters [Garcia et al. Phys. Rev. B, 75, 045439 (2007)]. The procedure has been extended and applied to predict the absorption coefficient of a quaternary nanocomposite consisting of Cu, Ag, and Au nanospheres embedded in a SiO2 host matrix. Significant enhancement of the absorption coefficient is observed over the spectral range 350-800 nm. The magnitude of this enhancement can be controlled by varying the nanosphere diameter and the individual metal volume fraction with respect to the host matrix. We have determined the optimal composition resulting in enhanced broadband (350nm-800nm) absorption of the solar spectrum using a simulated annealing algorithm. Fabricating such composite materials with a desired optical absorption has potential applications in solar energy harvesting.

cond-mat.mtrl-sci↗

arXiv2007

The convolution theorem for nonlinear optics

We have expressed the nonlinear optical absorption of a semiconductor in terms of its linear spectrum. We determined that the two-photon absorption coefficient in a strong DC-electric field of a direct gap semiconductor can be expressed as the product of a differential operator times the convolution integral of the linear absorption without a DC-electric field and an Airy function. We have applied this formalism to calculate the two-photon absorption coefficient and nonlinear refraction for GaAs and ZnSe using their linear absorption and have found excellent agreement with available experimental data.

physics.optics↗

arXiv2006

Self consistent determination of plasmonic resonances in ternary nanocomposites

We have developed a self consistent technique to predict the behavior of plasmon resonances in multi-component systems as a function of wavelength. This approach, based on the tight lower bounds of the Bergman-Milton formulation, is able to predict experimental optical data, including the positions, shifts and shapes of plasmonic peaks in ternary nanocomposites without using any ftting parameters. Our approach is based on viewing the mixing of 3 components as the mixing of 2 binary mixtures, each in the same host. We obtained excellent predictions of the experimental optical behavior for mixtures of Ag:Cu:SiO2 and alloys of Au-Cu:SiO2 and Ag-Au:H2 O, suggesting that the essential physics of plasmonic behavior is captured by this approach.

physics.optics↗

arXiv2006

A compound figure of merit for photonic applications of metal nanocomposites

Selecting nanocomposites for photonic switching applications requires optimizing their thermal, nonlinear and two-photon absorption characteristics. We simplify this step by defining a compound figure of merit (FOM_{C}) for nanocomposites of noble metals in dielectric based on criteria that limit these structures in photonic applications, i.e. thermal heating and two-photon absorption. The device independent results predict extremely large values of FOM_{C} for a specific combination of the metal and insulator dielectric constant given by ε_{h}=\frac{ε_{1}-ε_{2}}{2}, where ε_{h} is the dielectric constant of the host and ε_{1} and ε_{2} are the real and imaginary parts for the metal.

cond-mat.mtrl-sci↗