L. Ponce

Laser-Induced Breakdown Spectroscopy (LIBS) Quality Control and Origin Identification of Handmade Manufactured Cigars

Tobacco is an agricultural product originating in America that is obtained by processing the leaves of various plants of the genus Nicotiana tabacum. It is the inedible product occupying the most plantings in the world, according to a recent report from the United Nations Food and Agriculture Organization. It is consumed in various ways, but the most popular form of consumption is, undoubtedly, by smoking cigarettes. A particular segment of the tobacco industry is the manufacturing of handmade cigars, which for some third-world countries is an important source of income. There are different qualities of cigars, and a major problem is the adulteration that occurs, for example, when authentic high-quality leaves are replaced by lower quality leaves. A factor that influences the quality of the cigars is the smoke combustion process, which depends on several factors, particularly the composition of the leaves. We present a simple and quick technique for the quality control and origin identification of handmade cigars that measures the Mg/Ca ratios in the tobacco leaves and wrappers of the cigars using laser-induced breakdown spectroscopy.

Self-absorption influence on the optical spectroscopy of zinc oxide laser produced plasma

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.

On the use of shockwave models in laser produced plasma expansion

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

Pulsed Laser Deposition of PbTe in Monopulse and Multipulse Regime

We made a comparison between pulsed laser deposition with excitation in monopulse and multipulse regime. We find stoichiometric ablation when PLD is conducted with multipulse laser but the ablation process is less effective.

Burst Mode Q:switched Laser Pulses for Plasma Excitation in LIBS Analysis

The Laser Induced Breakdown Spectroscopy (LIBS), is a technique that has been firmly established for the rapid determination of the elemental composition (Cremers, 2006). It relies on material ablation by using a short duration laser pulse with high density energy enough to produce plasma. By analyzing the light emitted by the plasma, it is possible to determine the elemental composition of practically any material. This technique has significant advantages over other conventional analytical techniques (Cremers, 2007; Rusak et al., 1998; Song et al., 1997). For example, requires no sample preparation, may be performed in solid, liquid or gas phase in samples with any shape or dimension. Moreover, it allows an in-depth study in order to characterize the composition of multi-component material (Adamson et al., 2007; Radziemski et al., 1983). It is especially suitable for field work by offering the possibility of real-time analysis with high portability. Thanks the above mentioned advantages, the LIBS technique has experienced strong growth, which is reflected in a large and growing number of publications. LIBS is not a new technique: firsts laser-induced breakdown studies go back to the early 1960s and important application studies date from the 1980s with the work of Radziemski (Tognoni et al., 2002). A comprehensive review of LIBS development and applications through the mid-1990s was produced by Rusak et al.(Rusak et al., 1997). The technique has many attributes that make it an attractive tool for chemical analysis, particularly as regards its potential as a field-portable sensor for geochemical analysis. LIBS is relatively simple and straightforward, so skilled analysts are not required. Little to no sample preparation is required, which eliminates the possibility of adulteration of the sample through improper handling or storage or cross-contamination during sample preparation. LIBS provides a real-time response and simultaneous multi-element detection and analysis. The laser plasma is formed over a very limited spatial area, so that only a very small amount of sample (picograms to nanograms) is engaged in each laser micro-plasma event. All components of the instrument can be made small and rugged for field use and LIBS sensors can be operated either as a point sensor or in a standoff detection mode. The

Laser induced micro-cracks formation inside the glass, LIBS, and PILA measurements

An experimental measurement by using Laser Induced Breakdown Spectroscopy (LIBS) and Photoacoustic Induced by Laser Ablation (PILA), in order to monitoring the microcraks formation inside the glass induced by laser pulses is presented in this work. The laser was operated in both single pulse and multi-pulse Q:Switched regime using a passive Cr:YAG crystal as switching element. The LIBS spectra captured inside the glass avoid identifying the sample composition without influence of surrounding atmosphere like occurs if the spectra are obtained on the surface. On the other hand, the PILA signal permits to monitor the process and its dependence from the number and intensity of micro-pulses.

Bismuth thin films obtained by pulsed laser deposition

In the present work Bi thin films were obtained by Pulsed Laser Deposition, using Nd:YAG lasers. The films were characterized by optical microscopy. Raman spectroscopy and X-rays diffraction. It was accomplished the real time spectral emission characterization of the plasma generated during the laser evaporation process. Highly oriented thin films were obtained.

Automated system for acquisition and image processing for the control and monitoring boned nopal

This paper describes the design and fabrication of a system for acquisition and image processing to control the removal of thorns nopal vegetable (Opuntia ficus indica) in an automated machine that uses pulses of a laser of Nd: YAG. The areolas, areas where thorns grow on the bark of the Nopal, are located applying segmentation algorithms to the images obtained by a CCD. Once the position of the areolas is known, coordinates are sent to a motors system that controls the laser to interact with all areolas and remove the thorns of the nopal. The electronic system comprises a video decoder, memory for image and software storage, and digital signal processor for system control. The firmware programmed tasks on acquisition, preprocessing, segmentation, recognition and interpretation of the areolas. This system achievement identifying areolas and generating table of coordinates of them, which will be send the motor galvo system that controls the laser for removal

Ray trace algorithm description for the study of pump power absorption in double clad fibers.

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 plans. The algorithm can evaluate thousands of ray paths in sequence and its corresponding pump absorption in each of the elements of the fiber according to the Lambert-Beer law. The beam path is evaluated in 3 dimensions considering the losses by reflexion and refraction in the faces and within the fiber. Due to its flexibility, the algorithm can be used to study the ray propagation in single mode or multimode fibers, bending effects in fibers, variable geometries of the inner clad and the core, and could also be used to study tappers.

Optical detection of nopal spines for laser de-thorning process

A new optical method for detection of spines during the laser de-thorning process is presented. The spines detection is performed by on-line measurement of reflectance using a low power 532 nm, CW Nd:YAG laser. Its demonstrated that the method avoids enhancing the throughput and efficiency of laser dethorning of opuntia.