Fernando C. Alvira

Application of laser-induced breakdown spectroscopy (LIBS) and neural networks to olive oils analysis.

The adulteration and traceability of olive oils are serious problems in the olive oil industry. In this work, a method based on laser-induced breakdown spectroscopy (LIBS) and neural networks (NNs) has been developed and applied to the identification, quality control, traceability, and adulteration detection of extra virgin olive oils. Instant identification of the samples is achieved using a spectral library, which was obtained by analysis of representative samples using a single laser pulse and treatment by NNs. The samples used in this study belong to four countries. The study also included different regions of each country. The results obtained allow the identification of the oils tested with a certainty of more than 95%. Single-shot measurements were enough for clear identification of the samples. The method can be developed for automatic real-time, fast, reliable, and robust measurements, and the system can be packed into portable form for non-specialist users.

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.

Qualitative evaluation of Pb and Cu in fish using laser-induced breakdown spectroscopy with multipulse excitation by ultracompact laser source

We show a new laser-induced breakdown spectroscopy (LIBS) setup based on a small, ultracompact, and low-cost excitation source developed by the authors. The laser is a compact Nd:YAG laser emitting in the multipulse Q-switch regime and is capable of delivering a bunch of pulses with a total energy up to 300 mJ. The developed system is applied to the analysis of Pb and Cu contaminants on fish. LIBS spectra were obtained from scales, muscle, and skin of fresh and frozen samples. The developed excitation source is able to detect 0.25 mg/Kg and 0.20 mg/Kg of Pb and Cu, respectively. In this way, the equipment seems to be adequate to achieve a screening analysis of those contaminants.

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.

Laser-induced breakdown spectroscopy (LIBS) analysis of laser processing in active crystal with nanosecond laser pulses.

Laser-induced breakdown spectroscopy (LIBS) analysis is applied to study the ablation threshold and the main plasma features of active crystals used for laser processing with Nd3+ ions. The experiments were conducted by using nanosecond laser pulses from a neodymium-doped yttrium aluminum garnet (Nd : YAG) laser and its harmonics. In particular, we have studied the ablation process in SBN, strontium barium niobate (Sr x Ba1–xNb2O6, x = 0.6), and SBN, sodium barium niobate (Ba2NaNb5O15), nonlinear and ferroelectric crystals. Two different ablation regimes have been identified by LIBS analysis with high sensitivity compared with the standard method of hole-diameter measurement. Analyzing spectroscopically the plasma emission, we have found a particular behavior with the excitation wavelength. For example, the electronic density and temperature in SBN-generated plasmas present an abnormal behavior with the excitation wavelength. We therefore conclude that the energy gap corresponding to these crystals plays an important role in describing this fact. Hence, the resonant ablation in doped crystals can be a suitable point for exploration in further works in order to use the plasma performances to optimize the laser processing by nanosecond pulses for technological applications.

Time resolving imaging spectroscopy applied to the analysis of plasmas generated by pulsed lasers

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.