Papers by Cesar Costa Vera
Proponemos modificaciones de las ecuaciones de Bloch ópticas convencionales para un sistema molec... more Proponemos modificaciones de las ecuaciones de Bloch ópticas convencionales para un sistema molecular, cuando consideramos los efectos de acoplamiento intramolecular. Modelamos la molécula aislada como curvas de energía de Born-Oppenheimer que consisten en dos estados electrónicos cruzados descritos como potenciales armónicos, con los mínimos desplazados en coordenadas nucleares y energía. Consideramos dos estados vibracionales y una perturbación, que puede surgir de una correlación residual electrón-electrón y/o términos de acoplamiento spin-órbita en el Hamiltoniano del sistema, causando la separación de las dos curvas según la regla del cruce evitado. Las ecuaciones extendidas de Bloch ópticas permiten establecer la dinámica de un sistema molecular de estados adiabáticos sujeto a la interacción de un reservorio térmico e interactuando con campos electromagnéticos. En las ecuaciones se observa que haciendo nulo el factor de acoplamiento intramolecular, se recuperan las ecuaciones ...
Journal of Vacuum Science & Technology B
Graphene has attracted special attention due to its mechanical and electrical properties. In this... more Graphene has attracted special attention due to its mechanical and electrical properties. In this work, we describe the effects of sub-10 keV electron beam irradiation on the electrical conductivity of few-layer graphene films deposited on a glass substrate. The irradiation process was performed in vacuum at 10–6 Torr for 30 min per sample. The superficial chemical structure and optical properties of the samples were evaluated before and after electron irradiation using spectroscopic techniques (UV-Vis, Raman, and XPS), and the Van der Pauw method was used to determine the sheet resistance. It was found that the sheet resistance and the defect density decrease as the energy of incident electrons increases. For instance, the sheet resistance has been reduced by 17.3% after the sample was irradiated with a 10 keV electron beam. This could be explained by the reduction of defect density on the irradiated samples caused by the removal of oxygen content on graphene flakes, estimated by R...
Photodiagnosis and photodynamic therapy, Jan 24, 2017
The aims of this study were to determine the spatial and temporal theoretical distribution of the... more The aims of this study were to determine the spatial and temporal theoretical distribution of the concentrations of Protoporphyrin IX, (3)O2 and doses of (1)O2. The type II mechanism and explicit dosimetry in photodynamic therapy were used. Furthermore, the mechanism of respiration and cellular metabolism acting on (3)O2 were taken into account. The dermis was considered as an absorbing and a scattering medium. An analytical solution was used for light diffusion in the skin. The photophysical, photochemical and biological effects caused by PDT with the initial irradiances of 20, 60 and 150mW/cm(2) were studied for a time of exposure of 20min. and a maximum depth of 0.5cm. We found that the initial irradiance triples its value in 0.02cm and that almost 100% of PpIX is part of the dynamics of reactions in photodynamic therapy. Additionally, with about 40μMof (3)O2 there is a balance between the consumed and supplied oxygen. Finally, we determined that with 60mW/cm(2), the highest dose...
The European Physical Journal D
We investigate the strong-field ion emission from the surface of isolated silica nanoparticles ae... more We investigate the strong-field ion emission from the surface of isolated silica nanoparticles aerosolized from an alcoholic solution, and demonstrate the applicability of the recently reported near-field imaging at 720 nm [Rupp et al., Nat. Comm., 10(1):4655, 2019] to longer wavelength (2 $$\mu $$ μ m) and polarizations with arbitrary ellipticity. Based on the experimental observations, we discuss the validity of a previously introduced semi-classical model, which is based on near-field driven charge generation by a Monte-Carlo approach and classical propagation. We furthermore clarify the role of the solvent in the surface composition of the nanoparticles in the interaction region. We find that upon injection of the nanoparticles into the vacuum, the alcoholic solvent evaporates on millisecond time scales, and that the generated ions originate predominantly from covalent bonds with the silica surface rather than from physisorbed solvent molecules. These findings have important imp...
Revista Mexicana De Fisica, 2015
Se propone un experimento para la medicion de la constante de difusividad termica de muestras liq... more Se propone un experimento para la medicion de la constante de difusividad termica de muestras liquidas y sistemas coloidales de nano-particulas utilizando el efecto de lente termica inducida por un diodo laser modulado en frecuencia. El metodo consiste en medir la senal fototermica en funcion de la frecuencia de modulacion del laser. A partir de la grafica experimental obtenida, es posible estimar la difusividad termica de la muestra si se conoce el radio del haz del laser dentro de la misma. El experimento es calibrado por medio de la estimacion de la difusividad termica del etanol. Los coeficientes difusividad termica de soluciones acuosas de Azul Brillante FCF y sistemas de nanoparticulas de plata tambien son estimadas indicando un incremento de hasta un orden de magnitud del sistema de nanoparticulas en relacion al fluido base. Los resultados obtenidos muestran que el metodo es robusto, con un costo de implementacion reducido y con la sensibilidad necesaria para caracterizar ter...
Abstract: Previous work by one of the authors has shown the dependence of the Rayleigh-type optic... more Abstract: Previous work by one of the authors has shown the dependence of the Rayleigh-type optical mixing (RTOM) signal intensity on the incident pump and probe frequencies for different values of the ratio of relaxation times k = T 1 / T 2 . In this work an inverse problem methodology is defined to determine the ratio of the relaxation times k from sparse and/or noisy incident pump and probe frequency data in order to reconstruct the full field RTOM signal intensity. The simulated results show a robust procedure which points to potential efficient experimental application, to be pursued in the near future. Resumen: Trabajo previo de uno de los autores ha demostrado la dependencia de la intensidad de la senal de mezcla optica tipo Rayleigh (RTOM) en la frecuencia de bombeo y de prueba para valores diferentes de relacion de tiempos de relajacion k = T 1 / T 2 . En este trabajo se define una metodologia de problema inverso para determinar la relacion de tiempos de relajacion k de dat...
Beilstein Journal of Nanotechnology, 2020
In this work, monodisperse BiFeO3 nanoparticles with a particle diameter of 5.5 nm were synthesiz... more In this work, monodisperse BiFeO3 nanoparticles with a particle diameter of 5.5 nm were synthesized by a nanocasting technique using mesoporous silica SBA-15 as a hard template and pre-fabricated metal carboxylates as metal precursors. To the best of our knowledge, the synthesized particles are the smallest BiFeO3 particles ever prepared by any method. The samples were characterized by X-ray powder diffraction, transmission electron microscopy and UV–vis diffuse reflectance spectroscopy. The phase purity of the product depends on the type of carboxylic acid used in the synthesis of the metal precursors, the type of solvent in the wet impregnation process, and the calcination procedure. By using tartaric acid in the synthesis of the metal precursors, acidified 2-methoxyethanol in the wet impregnation process and a calcination procedure with intermediate plateaus, monodisperse 5.5 nm BiFeO3 nanoparticles were successfully obtained. Furthermore, the nanoparticles were applied in photod...
Optica Pura y Aplicada, 2015
This work studies the spatial propagation of the Four-Wave Mixing (FWM) signal of a molecular sys... more This work studies the spatial propagation of the Four-Wave Mixing (FWM) signal of a molecular system (malachite green) with two electronic levels immersed in a thermal bath, under a perturbative treatment at all order in the pump field and to first order in the probe and signal fields. Using the Optical Stochastic Bloch Equations OSBE, we present three approximations, two of them with analytical solutions and the third with a numerical approach, where the effects of the variation of pump intensity through the path optical are considered. We compare these results with the analogous in absence of the thermal reservoir. The stochastic effects induced by the solvent, due to the experimental conditions as relaxation times, chemical concentration of the solution and optical frequencies of the fields, diminishes the intensity responses compared with the same in absence of the bath.
Revista Mexicana De Fisica, 2017
Carbon nanoparticles (CNPs) have been synthesized by laser ablation of polycrystalline graphite i... more Carbon nanoparticles (CNPs) have been synthesized by laser ablation of polycrystalline graphite in water using a pulsed Nd:YAG laser (1064 nm) with a width of 8 ns. Structural and mesoscopic characterization of the CNPs in the supernatant by Raman spectroscopy provide evidence for the presence of mainly two ranges of particle sizes: 1-5 nm and 10-50 nm corresponding to amorphous carbon and graphite NPs, respectively. These results are corroborated by complementary characterization using atomic force microscopy (AFM) and transmission electron microscopy (TEM). In addition, large (10-100 µm) graphite particles removed from the surface are essentially unmodified (in structure and topology) by the laser as confirmed by Raman analysis.
Chemical Physics Letters, 2020
Abstract We analyze the statistical averages over a set of realizations of the random variable in... more Abstract We analyze the statistical averages over a set of realizations of the random variable in the Stochastic Optical Bloch equations, using Novikov's sufficient condition theorem. We consider a system on an adiabatic basis interacting with an external field in the presence of a thermal reservoir. We analyzed both for delta-correlated functions (white noise) and situations associated with Ornstein-Uhlenbeck processes (OUP) in colored noise. The effects of thermal reservoir and intramolecular coupling generate an effective transversal relaxation time. In the case of white noise, the resulting optical Bloch equations can be solved algebraically, unlike colored noise cases that requires numerical techniques.
Optica
Molecular adsorbate reactions on nanoparticles play a fundamental role in areas such as nano-phot... more Molecular adsorbate reactions on nanoparticles play a fundamental role in areas such as nano-photocatalysis, atmospheric, and astrochemistry. They can be induced, enhanced, and controlled by field localization and enhancement on the nanoparticle surface. In particular, the ability to perform highly controlled near-field-mediated reactions is key to deepening our understanding of surface photoactivity on nanosystems. Here, using reaction nanoscopy, we experimentally demonstrate all-optical nanoscopic control of surface reaction yields by tailoring the near fields on nanoparticles with waveform-controlled linear and bicircular two-color laser pulses, respectively. We observe site-selective proton emission from the dissociative ionization of adsorbate molecules on Si O 2 nanoparticles as a function of the polarization and relative phase of the two-color pulses. The angularly resolved close-to-uniform mapping between the surface reaction yields and the measured ion momentum enables the ...
Frontiers in Optics / Laser Science, 2020
3． 結果及び考察 3.1 基本統計値の動向及びそれら相関 ' ' My σy ESt Sy tb op tb op op op Sn Dn /My tb op tb op t op/b op ... more 3． 結果及び考察 3.1 基本統計値の動向及びそれら相関 ' ' My σy ESt Sy tb op tb op op op Sn Dn /My tb op tb op t op/b op op t op b op op op tb op-. My σy Sy 図 1 理科基本 4 科目基本統計通年値比
Latin America Optics and Photonics Conference, 2018
Revista Mexicana De Fisica, 2016
In this work, the thermal reservoir effects over the absorptive and dispersive nonlinear optical ... more In this work, the thermal reservoir effects over the absorptive and dispersive nonlinear optical properties of a two-level molecular system in presence of classical electromagnetic fields, were modeled. The collective effects proper of the thermal reservoir are modeled as a time dependent frequency, whose manifestation is the broadening of the upper level according to a prescribed random function. Using the stochastic optical Bloch equations, analytical expression for the nonlinear induced susceptibilities and absorptive and dispersive optical properties, were obtained. Numerical calculations were carried out to construct surfaces corresponding to these optical properties as a function of the pump-probe frequency detuning, relationships between the longitudinal and transversal relaxation times, and molecular concentration of solute. Finally, we see an attenuation of these optical responses by the solvent effects and the high pump-intensity.
Journal of Photochemistry and Photobiology A: Chemistry, 2021
Abstract Doped and undoped Bi1-xMxFeO3 porous networks (M = La, Gd, Nd; x = 0, 0.03, 0.05, 0.10) ... more Abstract Doped and undoped Bi1-xMxFeO3 porous networks (M = La, Gd, Nd; x = 0, 0.03, 0.05, 0.10) were synthesized by a facile glycine-nitrate combustion technique. The samples were analyzed by X-ray powder diffraction, scanning electron microscopy and UV-vis diffuse reflectance spectroscopy. For the first time, these Bi1-xMxFeO3 porous networks were applied in photocatalytic degradation reactions in aqueous solution under visible light irradiation using the dye Rhodamine B as a model. Our studies reveal that the type of rare-earth dopant as well as its concentration has no impact on phase purity and particle morphology and that the dopant significantly affects the optical absorption properties: the micrometer sized porous networks exhibited band gap values and optical absorption properties similar to those reported for nanometer sized samples. Furthermore, all samples showed enhanced photocatalytic activities. Based on its highest overall photocatalytic activity, Bi0.95Gd0.05FeO3 was chosen for stability, optimization and mechanistic experiments. Notably, the Bi0.95Gd0.05FeO3 photocatalyst not only demonstrated very high efficiencies but also a remarkable stability under visible light irradiation, much superior than those of doped Bi1-xMxFeO3 nanoparticles reported previously. This constitutes an important step towards industrial wastewater treatment applications. Under optimal reaction conditions, complete degradation of Rhodamine B was achieved in 1 hour. The possible mechanism in the photodegradation process has been discussed in detail on the basis of radical trapping experiments.
ACS Photonics, 2020
Ultrafast light-induced molecular reactions on aerosolized nanoparticles may elucidate early step... more Ultrafast light-induced molecular reactions on aerosolized nanoparticles may elucidate early steps in the photoactivity of nanoparticles with potential impact in fields ranging from chemistry and m...
Revista Politécnica, 2019
Usando las ecuaciones Ópticas de Bloch y considerando un sistema molecular que interactúa con un ... more Usando las ecuaciones Ópticas de Bloch y considerando un sistema molecular que interactúa con un reservorio térmico, derivamos expresiones analíticas para las propiedades ópticas no lineales en la espectroscopia de mezcla de cuatro ondas. En este trabajo se introducen diferentes metodologías para el estudio de las polarizaciones macroscópicas y susceptibilidades ópticas no lineales. En un sistema de dos niveles, hemos considerado una frecuencia dependiente del tiempo para describir los efectos colectivos del reservorio térmico, cuya manifestación es el ensanchamiento del nivel superior según una función aleatoria prescrita. Aquí, las respuestas ópticas son calculadas mediante una metodología basada en el promedio de la coherencia obtenida por la resolución de las ecuaciones de Bloch ópticas estocásticas. Evaluamos las susceptibilidades ópticas a diferentes frecuencias, representadas como superficies numéricas para el comportamiento de las respuestas ópticas, en función del factor de...
Materials Research Express, 2019
BiFeO3 nanoparticles with controlled particle size were synthesized via a facile co-precipitation... more BiFeO3 nanoparticles with controlled particle size were synthesized via a facile co-precipitation method. The samples were characterized by X-ray powder diffraction, transmission electron microscopy, atomic force microscopy and UV–vis diffuse reflectance spectroscopy. By controlling the timing of base addition during the co-precipitation process the particle size can be controlled easily. It was found that longer base addition times, i.e. slower dropping rates, resulted in smaller particle sizes exhibiting narrower band gaps. The smallest BiFeO3 particles prepared by this method are best described as circular flake-like nanoparticles with a diameter of 10-20 nm and a height of approximately 2.5-7 nm. To the best of our knowledge, these particles are the smallest BiFeO3 particles ever prepared by a co-precipitation method. Furthermore, our synthetic protocol allows the facile synthesis of size-tunable, pure-phase BiFeO3 nanoparticles with a low concentration of surface defects and local strain all leading to excellent efficiencies in photodegradation reactions of Rhodamine B in an aqueous solution under visible light irradiation. We show that the different particle sizes affected largely the resulting band gaps as well as the photocatalytic activity of the corresponding samples leading to narrower band gaps and improved photocatalytic activity in smaller particles.
Results in Physics, 2018
This study aims to analyze the individual characteristics of transmigrants in extransmigration vi... more This study aims to analyze the individual characteristics of transmigrants in extransmigration villages within Jambi Province, analyze aspects of transmigrant transmigration in the former transmigration villages within Jambi Province, and analyze employment in ex-transmigration villages within Jambi Province. This study was designed by collecting primary data. Research location in 6 (six) sample villages in 3 (three) Districts in three districts in Jambi Province. The research instrument used questionnaires to interview 168 households as respondents. Sampling by using Random Number Generated (RNG). The method of analysis used is descriptive quantitative and quantitative descriptive.The results found : 1) Average age of family head 64,31 years old. As many as 70.51% of those interviewed did not have a job. The largest part of the family head is male. Elementary education level/ equal to 45,76 percent. 2) The province's biggest origin is Central Java. Percentage of General Transmigration (88.10%). The main reason for joining transmigration is for the better future. The arrival of the origin is a direct transmigration. Number of household members carried between 3-4 people. 3) The land mastery of 2.45 Ha. Field of business is the most widely occupied agricultural sector (92.95%), and most as a rough worker. Research suggests that in the welfare context it is necessary to provide training for transmigrant in the field of skills, and the government should make alternatives to the future not dependent on existing land and they are not trapped only in the agricultural sector to anticipate the future, so as to increase the use of land towards a more productive. 2) Research on transmigration should be continued with regard to welfare, especially for more micro-scale studies at the household level.
SPIE Proceedings, 2016
Optical coherence tomography (OCT) is one of the most advanced optical measurement techniques for... more Optical coherence tomography (OCT) is one of the most advanced optical measurement techniques for complex structure visualization. The advantages of OCT have been used for surface and subsurface defect detection in composite materials, polymers, ceramics, non-metallic protective coatings, and many more. Our research activity has been focused on timefrequency spectroscopic analysis in OCT. It is based on time resolved spectral analysis of the backscattered optical signal delivered by the OCT. The time-frequency method gives spectral characteristic of optical radiation backscattered or backreflected from the particular points inside the tested device. This provides more information about the sample, which are useful for further analysis. Nowadays, the applications of spectroscopic analysis for composite layers characterization or tissue recognition have been reported. During our studies we have found new applications of spectroscopic analysis. We have used this method for thickness estimation of thin films, which are under the resolution of OCT. Also, we have combined the spectroscopic analysis with polarization sensitive OCT (PS-OCT). This approach enables to obtain a multiorder retardation value directly and may become a breakthrough in PS-OCT measurements of highly birefringent media. In this work, we present the time-frequency spectroscopic algorithms and their applications for OCT. Also, the theoretical simulations and measurement validation of this method are shown.
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Papers by Cesar Costa Vera