Luis Ponce Cabrera | Instituto Politécnico Nacional (original) (raw)

Papers by Luis Ponce Cabrera

The pulse laser ablation (PLA) as a new method for spines elimination of Prickle Pear fruit is pr... more The pulse laser ablation (PLA) as a new method for spines elimination of Prickle Pear fruit is presented. The new technique works thanks to the use of the pulsed light that is absorbed in a selective way, specifically in the spines. An optical characterization of both spine and cactus cortex allows to find the most convenient pulse energy for selective absorption. By using laser-induced breakdown spectroscopy (LIBS) in Q:Switch and free-running regimes, it is possible to control the process in real time and to check the cleaning results online. The feasibility of performing the laser ablation of spines without visible damages to the substrate was proved by the optical microscopy observation.

Sumario. La espectroscopia de plasma inducido por láser (LIBS) puede ser considerada como una de ... more Sumario. La espectroscopia de plasma inducido por láser (LIBS) puede ser considerada como una de las técnicas más dinámicas y prometedoras en el campo de la espectroscopia analítica. LIBS se ha convertido en una poderosa alternativa en aplicaciones desde la exploración geológica hasta la inspección industrial, incluido el monitoreo medioambiental, el análisis biomédico, el estudio de obras patrimoniales, la seguridad y defensa, entre otros. Los avances en la instrumenta-ción LIBS han permitido mejorar progresivamente los servicios y calidad de análisis, sobre la base de un mejor conoci-miento de los principios de la tecnología. Recientemente, los sistemas de doble pulso han facilitado una mejor dosifica-ción de la energía, la mejora de la relación señal-ruido y el estudio de las diferentes etapas del proceso. Los nuevos avances como sistemas multi-pulsos entre otros, aun por explorar, deben ofrecer nueva información para avanzar en este conocimiento. Por último, lo que hace a esta tecnología ser realmente atractiva, es la aptitud para ser empleada en con-diciones de campo, o para la detección de la composición elemental a largas distancias. En esta presentación se discuten los diseños de una instrumentación portátil, compacta y de bajo costo, que puede mejorar sustancialmente las posibili-dades de LIBS. Abstract. Laser Induced Breakdown Spectroscopy (LIBS), can be considered as one of the most dynamic and promising technique in the field of analytical spectroscopy. LIBS has turned into a powerful alternative for a wide front of applications , from the geological exploration to the industrial inspection, including the environmental monitoring, the biomedical analysis, the study of patrimonial works, the safety and defense. The advances in LIBS instrumentation have allowed improving gradually the analysis services and quality, on the basis of a better knowledge of the technology principles. Recently, systems of double pulse have facilitated a better dosing of energy, the improvement of the signal-noise relation and the study of the different process stages. Femtosecond lasers offers the possibility of study in detail the ablation and atomic emission processes. New advances like multi-pulse or multi-wavelentgh systems-in fact stilling without exploring, must offer new information to advance in this knowledge. Finally, which it does to this technology really attractive, is the aptitude to be employed in field conditions, or for the detection of the elementary composition at long distances. In this presentation there are discussed the designs of portable instrumentation, compact and low cost, which can improve substantially the LIBS possibilities.

Sumario. Se presentan métodos y configuraciones para el diseño de resonadores ópticos en láseres ... more Sumario. Se presentan métodos y configuraciones para el diseño de resonadores ópticos en láseres de estado-sólido de alta potencia operando en régimen pulsado de generación libre. Para resonadores de alta potencia emitiendo en el modo fundamental, se propone un método para el diseño de resonadores con zonas de estabilidad unidas. En el caso de reso-nadores multimodo se introducen dos configuraciones que permiten maximizar la eficiencia total del láser a partir de la compensación del astigmatismo inducido por la excitación de medio activo. La primera de las dos configuraciones con-siste en un resonador en anillo triangular. Los resultados de esta configuración se discuten teóricamente, mostrando que es posible compensar el astigmatismo de la lente térmica prácticamente en un 100%, sin embargo, sólo se consigue esta corrección en un rango muy estrecho de potencias de bombeo. La segunda de las configuraciones propone un resonador de doble medio activo, rotando 90 grados uno respecto al otro alrededor del eje óptico, donde cada uno de ellos funciona como una lente astigmática con el mismo poder dióptrico. La caracterización experimental de un resonador con doble medio activo de YAG:Nd diseñado según esta última configuración, corrobora los resultados encontrados teóricamente. Se encuentra que durante el intervalo de potencia para el cual se compensa el astigmatismo, la eficiencia se mantiene constante aún con el incremento de la potencia de excitación y el consecuente aumento del poder dióptrico de la lente térmica Abstract. Methods and configurations for the design of high power solid-state pulsed laser resonators, operating in free running, are presented. For fundamental mode high power resonators, a method is proposed for the design of a resonator with joined stability zones. In the case of multimode resonators, two configurations are introduced for maximizing the laser overall efficiency due to the compensation of the astigmatism induced by the excitation. The first configuration consists in a triangular ring resonator. The results for this configuration are discussed theoretically, showing that it is possible to compensate the astigmatism of the thermal lens virtually in a 100%; however this is only possible for a specific pumping power. The second configuration proposes a dual-active medium resonator, rotated 90 degree one from the other around the optical axis, where each active medium acts as an astigmatic lens of the same dioptric power. The reliability of this configuration is corroborated experimentally using a YAG:Nd dual-active medium resonator. It is found that in the pumping power range where the astigmatism compensation is possible, the overall efficiency is constant , even when increasing the excitation power with the consequent increase of the thermal lens dioptric power. Palabras claves. Diseño de resonadores 42.60.Da, estabilidad del resonador 42.60.Lh

It is demonstrated that Photo-acoustic Induced by Laser Ablation (PILA) technique is suitable for... more It is demonstrated that Photo-acoustic Induced by Laser Ablation (PILA) technique is suitable for the real time control and monitoring of the de-thorning process of nopal vegetable using pulsed laser. Two methods for detection of thorns are proposed; the first one uses the photo-acoustic amplitude and the second one is based in the harmonic composition of photo-acoustic signals. The latter detects clearly, thorns positions, differentiating them from other features that could exist in the nopal cortex. Harmonic composition of photo-acoustic signals also allows defining when thorns have been removed. Finally, it is obtained a characteristic pulse duration that, for the used energy range, maximizes thorns removal.

Es difícil imaginar una invención que haya tenido un impacto tan grande como ha ocurrido con el l... more Es difícil imaginar una invención que haya tenido un impacto tan grande como ha ocurrido con el láser en la medicina. Gracias a sus ventajas, esta tecnología se ha convertido en una herramienta auxiliar de gran valor para muchos tratamientos médicos, por lo cual hoy podríamos citar decenas de aplicaciones que van desde los tratamientos de regeneración de tejidos con láseres de baja potencia, hasta las sofisticadas operaciones de corrección de miopía, que se han vuelto tan populares.

Análisis de plasmas inducidos por láser con excitación multipulso para el proceso de ablación de ... more Análisis de plasmas inducidos por láser con excitación multipulso para el proceso de ablación de areolas de Tuna

Interaction of medium to high peak power laser pulses with solid materials produces a plasma that... more Interaction of medium to high peak power laser pulses with solid materials produces a plasma that expands supersonically. Expansions of such plasmas have been studied and several models have been proposed to describe it. This work presents a study of the expansion of laser produced plasmas in both vacuum and gas environment by using Langmuir probe and photography. It compares some of the most used models to identify that which better describes the expansion process. In vacuum, such process is properly described by the Anisimov model. However when expanding in a background gas it is found that the Sedov-Taylor model fits properly the position of generated shockwave but overestimates both kinetic energy and pressure of the expanding plasma. Such problem is solved by using a modification of the Freiwald-Axford model. Finally it is demonstrated that after the plasma stopping distance the plasma inters in a diffusive regime. 1. Introduction Studies on the expansion of laser produced plasma can be traced back to as early as the 60s, where both the in vacuum [1] and in gas background [2] expansion was analyzed. Different models have been proposed to describe these expansions [3-6], most of them using a gas-dynamic approach and describing both temporal and spatial behavior of macroscopic parameters, such as density, temperature and expansion velocity. Knowledge of these parameters is important not only to gain inside on the nature of the plasma it also allows to define how plasma species interact among them and with surrounding gas or solid. Such interactions are of great importance in processes like pulsed laser deposition (PLD) where chemical reactions or sputtering are important factors to produce high quality thin films. One of the most used [7-12] model for describing laser produced plasma expansion in a gas environment is the Sedov-Tylor (S-T) model for the description of shock waves in nuclear explosions [13]. This can be understood, firstly, by analyzing the basic assumptions in the strong explosion theory: (i) a large amount of energy E p is released instantaneously from a small (negligible) volume, (ii) the mass of the energy source m p is negligible compared with the mass of the gas background swept by the shock wave and (iii) the pressure exerted by the explosion over the gas should be greater than the pressure in the unperturbed background gas. Secondly to a straightforward to use set of equation, given by this model, relating shock wave expansion velocity and the plasma parameters mentioned before.

Start your abstract here… Time resolved imaging spectroscopy were used to study the spatial and t... more Start your abstract here… Time resolved imaging spectroscopy were used to study the spatial and temporal evolution of LIBS (Laser Induced Breakdown Spectroscopy) plasmas generated in Cu substrates by laser pulses of different duration. Long laser pulses (microsecond) and short laser pulses (nanosecond) as well as multipulse emission were used for excitation. Analysis was made by using an imaging spectrometer with time resolved detection. Results show that the use of long laser excitation pulses produce emission spectra with the same signal to noise ratio, but with lower resolution than those produced with shorter ones. The different species generated in LIBS experiments as neutral or single ionized have a different spatial distribution inside the plasma. We demonstrated that using spatial discrimination procedures is possible to obtain spectra with the same signal to noise ratio than those obtained with a gating detector. In this case an appreciable advantage in cost reduction is obtained by replacing the gating detector by a cheap screen.

Optical spectroscopy is used to study the laser ablation process of ZnO targets. It is demonstrat... more Optical spectroscopy is used to study the laser ablation process of ZnO targets. It is demonstrated that even if Partial Local Thermal Equilibrium is present, self absorption process leads to a decrease of recorded lines emission intensities and have to be taken into account to obtain correct values of such parameters. It is presented a method that combines results of both Langmuir probe technique and Anisimov model to obtain correct values of plasma parameters. 1. Introduction Optical Spectroscopy is one of the key techniques to characterize plasmas, as it offers several methods to extract densities and temperatures of species that form the plasma. Laser produced plasmas (LPP) are characterized by their intrinsic density and temperature gradient, which may induce strong self-absorption of emission from the core of the plasma, by less exited species on the edge of it. As a result, intensities of recorded self-absorbed emission lines are lower than they really are. The latter misleads plasma temperature and density values, calculated using intensity based spectroscopic methods. In order to correct such errors it is needed to take absorption into account. In this paper it is analyzed LPP from a zinc oxide target. It is demonstrated that for the used laser pulse energy fluence, recorded emission lines suffer a strong self-absorption. In order to extract proper plasma parameters it is presented a method that fits recorded spectra accounting for self-absorption and other plasma related phenomena like line shifting and broadening. Furthermore, calculus procedure uses Anisimov´s model [1] to up bound values of calculated plasma parameters.

This study presents the use of a portable Laser Induced Breakdown Spectroscopy (LIBS) prototype f... more This study presents the use of a portable Laser Induced Breakdown Spectroscopy (LIBS) prototype for determining the elemental composition of a metal jug. The system includes emission from a multiuse Q-switched Nd:YAG laser. By sampling at different points, the surface composition is determined. Furthermore, the presence of two layers of Pb and Cu and their thicknesses are determined through in-depth analysis.

TiN films were prepared by the Cathodic arc evaporation deposition method under different negativ... more TiN films were prepared by the Cathodic arc evaporation deposition method under different negative substrate bias. AFM image analyses show that the growth mode of biased coatings changes from 3D island to lateral when the negative bias potential is increased. Nanohardness of the thin films was measured by nanoindentation, and residual stress was determined using Grazing incidence X ray diffraction. The maximum value of residual stress is reached at −100 V substrate bias coinciding with the biggest values of adhesion and nanohardness. Nanoindentation measurement proves that the force-depth curve shifts due to residual stress. The experimental results demonstrate that nanohardness is seriously affected by the residual stress.

Size-selected TiN nanoclusters in the range of 4 to 20 nm have been produced by an ionized cluste... more Size-selected TiN nanoclusters in the range of 4 to 20 nm have been produced by an ionized cluster beam, which combines a glow-discharge sputtering with an inert gas condensation technique. With this method, by controlling the experimental conditions, it was possible to produce nanoparticles with a high control in size. The size distribution of TiN nanoparticles was determined before deposition by mass spectroscopy and confirmed by atomic force microscopy. The size distribution was also analyzed using a high-resolution transmission electron micrograph. The photoluminescence [PL] spectra of TiN nanoparticles at different sizes were also experimentally investigated. We reported, for the first time, the strong visible luminescence of TiN nanoparticles on Si (111) wafer due to the reduced size. We also discussed the PL intensity as a function of the nanoparticle size distribution.

An algorithm for the analysis of the double-clad fiber design is presented. The algorithm develop... more An algorithm for the analysis of the double-clad fiber design is presented. The algorithm developed in the MATLAB computing language, is based on ray tracing method applied to three-dimensional graphics figures which are composed of a set of planes. The algorithm can evaluate an arbitrarily large number of ray paths calculating the corresponding pump absorption in each of the fiber elements according to the Lambert–Beer law. The beam path is evaluated in three dimensions considering the losses by reflection and refraction both at the fiber faces and within the fiber. Due to its flexibility, the algorithm can be used to study the ray propagation in double-clad fiber with: i) variable geometries of the inner clad and the core; ii) different position of the core inside the inner clad; and iii) bending and tapper effects.

This paper presents the characterization of Opuntia samples whose thorns were removed by laser pu... more This paper presents the characterization of Opuntia samples whose thorns were removed by laser pulses. The characterization was performed by Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). In this study we performed a comparative analysis of samples before and after treatment by using a Nd:YAG laser emitting at 1064 nm with an energy variable of up to 0.9 J. It was determined that no significant morphological or compositional changes had taken place in the cactus epidermis due to the laser treatment.

Pulsed laser deposition of ZnO thin films, using KrF laser, is analysed. The films were deposited... more Pulsed laser deposition of ZnO thin films, using KrF laser, is analysed. The films were deposited on (001) sapphire substrates at 400 • C, at two different oxygen pressures (0·3 and 0·4 mbar) and two different target– substrate distances (30 and 40 mm). It is observed that in order to obtain good quality in the photoluminescence of the films, associated with oxygen stoichiometry, it is needed to maximize the time during which the plasma remains in contact with the growing film (plasma residence time), which is achieved by selecting suitable combinations of oxygen pressures and target to substrate distances. It is also discussed that for the growth parameters used, the higher probability for ZnO films growth results from the oxidation of Zn deposited on the substrate and such process takes place during the time that the plasma is in contact with the substrate. Moreover, it is observed that maximizing the plasma residence time over the growing film reduces the rate of material deposition, favouring the surface diffusion of adatoms, which favours both Zn–O reaction and grain growth.

TiO2 thin films were prepared on glass substrates using the PLD (Pulsed Laser Deposition) techniq... more TiO2 thin films were prepared on glass substrates using the PLD (Pulsed Laser Deposition) technique. In order to carry out the ablation process, a Nd:YAG laser was used emitting in 1064 nm wavelength at 10 Hz repetition rate, set up for operating in both single-pulse and multi-pulse regimes. A comparison of the deposition rate, the optical and morphological properties of the layers obtained from both ablation regimes was made, which showed that the multi-pulsed ablation produced layers with a higher surface quality and better optical properties.