Hernando Garcia

Southern Illinois University Edwardsville | SIUE · Department of Physics

Polarization rotation is an important parameter in the design of passive and active photonic components (optical isolators, magneto-optical valves, and magnetic field sensors). This effect is particularly important in materials with delocalized electrons and large atomic orbital moments like CdMnTe, which is an excellent candidate due to its large...

We report a giant intensity-dependent Faraday rotation in iron doped Cd 0.85 Mn 0.15 Te:Fe. Rotations of 12 o in magnetic field of 0.55T and intensities of 1.832 GW/cm ² can be achieved. This is 60 time larger than previously reported.

Polarization rotation is an important parameter in the design of passive and active photonic components (optical isolators, magneto-optical valves, and magnetic field sensors). This effect is particularly important in materials with delocalized electrons and large atomic orbital moments like CdMnTe, which is an excellent candidate due to its large...

Polarization rotation is an important parameter in the design of passive and active photonic components (optical isolators, magneto-optical valves, and magnetic field sensors). This effect is particularly important in materials with delocalized electrons and large atomic orbital moments like CdMnTe, which is an excellent candidate due to its large...

Polarization rotation is an important parameter in the design of passive and active photonic components (optical isolators, magneto-optical valves, and magnetic field sensors). This effect is particularly important in materials with delocalized electrons and large atomic orbital moments like CdMnTe, which is an excellent candidate due to its large...

We have studied the magneto-optical response of Cd1-xMnxTe when doped with two different elements (Ge and Fe) with a mean doping concentration of 5 × 1019 cm−3. Cd0.85Mn0.15Te doped with iron (Fe) has been explored as a solid-state gain medium for mid-IR laser sources, and Cd0.80Mn0.20Te with germanium (Ge) for use as a radiation detector. In this...

An F-scan nonlinear spectrometer is used to measure the two-photon absorption coefficient for CH3NH3PbBr3 perovskite films from 690 to 995 nm. This spectrometer uses an electrically focused tunable lens and a tunable femtosecondpulse laser (Mai Tai-HP) with a resolution of 5 nm. Two-band models and saturation irradiance corrections are used to fit...

Based on the F-scan technique, in this work we proposed a technique that measures semiconductors’ two-photon absorption coefficients through laser power variations. The technique, dubbed P-scan, uses an electrically-focus tunable lens to retrieve light transmittance signals in the linear and nonlinear absorption regimes. With the rate of the transm...

We are reporting, for the first time to our knowledge, measurement of the degenerate two-photon absorption (TPA) coefficient in Cd1-xMnxTe (x = 0.45) in a wide spectral range (690–1040 nm), with a 5 nm resolution. The spectral dependence of the TPA is modeled as a combination of a-a and f-f transitions. The time response is ultrafast at 780 nm with...

There is a pressing need to discover magneto-optical materials and devices with better performance and lower cost that operate at telecommunication wavelengths. Here we report the discovery of giant negative nonlinear refraction and nonlinear Faraday rotation at 1550 nm using an array of bimetallic Fe-Ag nanopyramids. This system exhibited a very l...

In this article, we show nanosecond switchable localized surface plasmon resonance (LSPR) dipole and quadrupole modes from silver (Ag) nanoparticles on fused quartz substrates. Nearly spherical Ag nanoparticles (contact angle of ~166○/+-9) were synthesized by Ultra Violet (UV) laser dewetting of Ag thin films under a glycerol fluid environment. Und...

Using an electrically focus tunable lens (EFTL) in an F-scan setup and a tunable femtosecond-pulse laser (Mai Tai HP), we were able to measure the degenerated two-photon absorption coefficient (in transmission) of CdS and ZnSe in an extended range of wavelengths (690-1040 nm), with a 5 nm resolution. The process of measuring takes less than 30 minu...

In this paper we present a modification to the recently proposed transmission F-scan technique, the differential F-scan technique. In the differential F-scan technique, the programmed focal distance in the electronic-tunable lens is modulated, allowing the light detector in the setup to record a signal proportional to the derivative of the signal r...

Using an Electrically Focus Tunable Lens (EFTL), a pair of integrating spheres and a tunable femtosecond-pulse laser, we were able to measure the nonlinear two-photon absorption (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 ap...

In this paper two-photon absorption coefficient $\beta$ and nonlinear refractive index ${n}_{2}$ have been measured at 1064 nm for a new two-dimensional (CH3(CH2)2NH3)2(CH3NH3)2Pb3Br10 hybrid perovskite. The nonlinear optical properties were measured using transmission and reflection F-scan techniques. As a reference, a three-dimensional CH3NH3PbBr...

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 ang...

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...

Plasmonic nanoparticles are amongst the most effective ways to resonantly couple optical energy into and out of nanometer sized volumes. However, controlling and/or tuning the transfer of this incident energy to the surrounding near and far field is one of the most interesting challenges in this area. Due to the dielectric properties of metallic si...

We implement an interferometric autocorrelation of a femtosecond optical pulse using an Electrically Focus Tunable Lens (EFTL). In this approach we eliminated the need of a mechanical translation stage, with an impressive resolution of 0.23 fs.

We have measured the two-photon absorption coefficients for CdS and ZnSe by using a new single beam setup based on the well-known Z-scan technique. This novel technique, which we have named " f-scan " , uses an electrically focus-tunable lens instead of a mechanical translation stage, simplifying the experimental setup and reducing dramatically the...

In this communication, a novel technique to measure the temporal width of an ultra-short optical pulse using an electrically focus-tunable lens (EFTL) is proposed and implemented (no need for a mechanical translation stage). The principle is based on the time delay experienced by the pulse when it passes through the deformed membrane of the EFTL as...

Many Physics students opt for a master’s degree in Physics without plans for pursuing a doctorate in the future. These students typically wish to find jobs in industry after receiving the M.S. degree. The traditional Physics master’s degree program, with courses mirroring those of the first year of a program leading to a Ph.D., is not addressed to...

Discovery of new plasmonic behaviors from nanostructured materials can be greatly accelerated by the ability to prepare and characterize their near-field behaviors with high resolution in a rapid manner. Here, an efficient and cost-effective way is reported to make 2D periodic nanostructures on electron-transparent substrates for rapid characteriza...

The localized surface plasmon resonance (LSPR) of nanoparticles can be a powerful and sensitive probe of chemical changes in nanoscale volumes. Here we have used the LSPR of silver (Ag) to study the oxidation kinetics of nanoscopic volumes of cobalt (Co) metal. Bimetal nanoparticles of the immiscible Co-Ag system prepared by pulsed laser dewetting...

The two-photon absorption (TPA) coefficient b and the nonlinear index of refraction n2 for bulk cuprous oxide (Cu2O) direct gap semiconductor single crystal have been measured by using a balance-detection Z-scan single beam technique, with an excellent signal to noise ratio. Both coefficients were measured at 790nm using a 65 fs laser pulse at a re...

Interaction of photons with matter at length scales far below their wavelengths has given rise to many novel phenomena, including localized surface plasmon resonance (LSPR). However, LSPR with narrow bandwidth (BW) is observed only in a select few noble metals, and ferromagnets are not among them. Here, we report the discovery of LSPR in ferromagne...

The Mie theory gives the exact solution to scattering from spherical particles while the Fresnel theory provides the solution to optical behavior of multilayer thin film structures. Often, the bridge between the two theories to explain the behavior of materials such as nanoparticles in a host dielectric matrix, is done by effective medium approxima...

The non-linear optical properties of CdS and ZnSe using a new setup which we have named “f-scan”. It uses an electrically-focus-tunable-lens instead of a mechanical translation stage. In this talk I will outline the theory, and experimental implementation.

Reduced degradation (oxidation) of silver nanoparticles (NPs) is achieved by contacting Ag with immiscible Co NPs. The relative decay of the plasmon peak (plot) shows that pure Ag NPs (blue dashed curve) decay by 25% in ca 20 days, whereas AgCo NPs last about 10 times longer, requiring nearly five months for a similar decay (red solid curve). The T...

Various forms of Si including amorphous Si (a-Si) are important photovoltaic (PV) materials. However, in order to improve the cost-to-performance aspects of Si solar cells, such as by enabling ultrathin (<500 nm) Si solar technology, new strategies are required to improve optical absorption within Si, which is a relatively poor absorber of light in...

We demonstrate a promising synthesis route based on pulsed laser dewetting of bilayer films (Ag and Co) to make bimetallic nanoparticle arrays. By combining experiment and theory we establish a parameter space for the independent control of composition and diameter for the bimetallic nanoparticles. As a result, physical properties, such as the loca...

of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

We have calculated the two photon absorption coefficient for Ge within the effective mass approximation for the direct as well as the indirect gap region. By including all the possible contributions to the nonlinear absorption based on the Ge band structure, we found excellent agreement with the recent experimental report on the two photon absorpti...

The optical properties of multi-metal nanocomposites made from Cobalt (Co), and Silver (Ag) are analyzed theoretically within the mean field approximation, and experimentally verified using absorption spectroscopy. The experimental system was modeled as a thin layer composed of hemispherical nanoparticles formed by grains of Co and Ag in contact wi...

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Silicon thin films over a glass substrate has been considerate an economical and viable alternative for the photovoltaic industry. Implementation of this technology will contribute to preserve a clean environment helping to reach a sustainable future. Nevertheless, by their own nature, Silicon thin films present small light absorption, and its elec...

Metallic nanoparticles embedded in dielectrics permit enhanced capture of light at specific wavelengths through excitation of plasmons, i.e. the quanta of coherent and collective oscillations of large concentrations of nearly free electrons. In order to maximize the potential of such enhanced absorption in useful tasks, such as the generation of ca...

The lower and upper bounds for the nonlinear susceptibility of a multi-component nanocomposite composed of a glass host and nanoparticles of multiple metals are calculated within the context of the Hashin–Shtrikman formulation. We have applied this effective medium theory to the following ternary composites: AgCu:SiO2 and AgAu:SiO2 in the form of m...

Metallic nanoparticles embedded in dielectrics permit enhanced capture of light at specific wavelengths through excitation of plasmons, i.e. the quanta of coherent and collective oscillations of large concentrations of nearly free electrons. In order to maximize the potential of such enhanced absorption in useful tasks, such as the generation of ca...

When an ultrathin metal film of thickness h (<20 nm) is melted by a nanosecond pulsed laser, the film temperature is a nonmonotonic function of h and achieves its maximum at a certain thickness h*. This is a consequence of the h and time dependence of energy absorption and heat flow. Linear stability analysis and nonlinear dynamical simulations tha...

Efficient broadband solar absorbing coatings could significantly enhance the performance of Si solar cells. Here, we present the design of novel SiO2-based nanomaterial coatings based on multimetal plasmonic absorption. By implementing an efficient homogenization procedure based on the tight lower bounds of the Bergman-Milton formulation [Garcia et...

The authors have expressed the nonlinear optical absorption of a semiconductor in terms of its linear spectrum. They 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 with...

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...

Experimental approaches for the synthesis of nanocomposites, mathematical models for the prediction of the process thermal cycles and particle size/spacing, and homogenization approaches for the prediction of the wavelength-dependent absorption of light by composite materials were presented. The design of multi-metal nanocomposites that maximize ab...

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 n...

Selecting nanocomposites for photonic switching applications requires optimizing their thermal, nonlinear, and two-photon absorption characteristics. The authors 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 app...

We have investigated the nanostructure and microstructure resulting from ns laser irradiation simultaneous with deposition of Co films on Si(001) substrates. The spatial order and length scales of the resulting nanopatterns and their crystalline microstructure were investigated as a function of film thickness h and laser energy density E using a co...

Most metals on SiO2 have a finite contact angle and are therefore subject to dewetting during thermal processing. The resulting dewetting morphology is determined primarily by nucleation and growth or instabilities. The dewetting mechanism implies a disordered spatial arrangement for homogeneous nucleation, but an ordered one for instabilities such...

The two-photon absorption coefficient of an indirect gap semiconductor (phonon-assisted two-photon absorption) in the presence of a strong dc-electric field applied perpendicular to the direction of propagation of the optical field is calculated using the formalism developed elsewhere (Aspnes 1996 Phys. Rev. B. 147 554). We show that depending on t...

Se diseñó un láser de CO 2 de flujo continuo, refrigerado con agua circulante en ciclo cerrado y con tubo de descarga DC desacoplado del resonador. Entre los espejos del resonador y las ventanas Brewster se dejó espacio suficiente para introducir dispositivos que permitan modular el láser, dejando la posibilidad de producir pulsos de alta potencia....

A 980 - nm pump-induced nonlinear refractive-index ( n 2 ) change in erbium-doped ( 20 - m ) and ytterbium-doped ( 20 - m ) fibers has been measured at 1064 nm by time-delayed photorefractive beam coupling in a copropagating and counterpropagating geometry. It was found that n 2 decreases at the wavelength of the probe beam when the pump beam is pr...

The $N$-photon absorption coefficient of a direct gap semiconductor under the influence of a uniform electric field perpendicular to the layer and neglecting excitonic effects is calculated. For $N=2$ we recover the familiar results for the low-field regime. The system also shows the same universal behavior as for the $N=1$ case. Below the ${E}_{g}...

We report a direct numerical model of the induced grating autocorrelation (IGA) based on the numerical solution of the nonlinear Schrödinger equation for an intense optical pulse that has experienced nonlinear distortion [notably, self-phase modulation (SPM) and stimulated Raman scattering (SRS)] after propagating through an optical fiber. Our nume...

We report for the first time, to our knowledge, a technique that has the capability to measure both the Raman gain coefficient and the nonlinear refractive index of an optical fiber, using the same experimental setup. This measurement utilizes the induced-grating autocorrelation (IGA) technique, which is based upon time-delayed four-beam coupling i...

The nonlinear refractive index n 2 of silica fiber (24 m) and erbium-doped fiber (10 m) is measured to within an accuracy of 5% by use of time-delayed photorefractive beam coupling of intense 53-ps, 1.064 - µ m pulses that experience self-phase modulation in the fibers. The resultant induced grating autocorrelation response yields a value of n 2 /...

The two-photon absorption coefficient and Kerr coefficient of bulk crystalline silicon are determined near the telecommunication wavelengths of 1.3 and 1.55 μm using femtosecond pulses and a balanced Z-scan technique. A phase shift sensitivity of the order of 1 mrad is achieved, enabling the accurate measurement of third-order nonlinear coefficient...

Summary form only given. The increasingly demanding application of erbium-doped fiber amplifiers (EDFA) in fiber optic communication systems (including solitons), requires a deep understanding of the effects of the pump laser on the optical properties of the amplifier at the signal level. Amplification provides by EDFAs is produced by optically pum...

form only given. Recent measurements of high optical nonlinearity in Si nanoclusters has generated interest in their potential use as an optical switch. The study of the nonlinear optical properties of Si nanoclusters (NCs) made by laser ablation and ion implantation techniques is motivated by the need for materials that exhibit large values of the...

A new technique to measure the nonlinear refractive index n 2 in optical fibers and semiconductor films has been developed. It is based on the time delay two-beam coupling of very intense picosecond laser pulses that have been self-phase modulated in the nonlinear optical medium. The two beams are coupled in a slow responding medium that is sensiti...

The nonlinear refractive index n2 of short lengths (<25 m) of a 20 m silica fiber were measured by photorefractive beam-coupling of 53 ps, 1064 nm pulses that experienced self-phase modulation (SPM) in the fiber. The resultant Induced Grating Autocorrelation (IGA) response yields a value of n2 and a calibration standard for the fiber. By coupling t...

Z-scan measurements were performed to determine the nonlinear optical properties of silicon nanoclusters fabricated by laser ablation