Gabriel M. Bilmes

Non-toxic, water-soluble photocalorimetric reference compounds for UV and visible excitation

Abstract A set of non-toxic, water-soluble photocalorimetric reference compounds has been characterized. These compounds are brilliant blue G, brilliant black BN, new coccine, indigo carmine, and tartrazine. Neutral aqueous solutions of all compounds are photochemically stable under UV–visible excitation (λ>300 nm). None of these dyes are fluorescent or show optical transients detectable by laser flash photolysis on the nano- to microsecond time scale. The relationship between the amplitude of the photoacoustic signal and the laser fluence is linear up to at least 350 J/m2. The fraction of absorbed energy delivered to the medium as heat within the integration time of the instrument (α) is equal to 1 for all of the samples, within the experimental error (±0.05). With the exception of tartrazine, no photoinduced structural volume changes were detected for any of the dyes.

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.

Acoustic detection of laser induced melting of metals

Real time detection of pulsed laser surface melting was performed by analyzing the photoacoustic signals produced on the samples. Comparison between the amplitudes of the transversal and longitudinal waves allowed us to identify the fluence thresholds for surface melting. The method was tested with AISI 304 stainless steel samples and the results obtained were checked against direct metallographic analysis.

Identification and Measurement of Dirt Composition of Manufactured Steel Plates Using Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used for the characterization of the main components of the surface residual dirt produced in cold-rolled steel plates as a consequence of the manufacturing stages. At laser fluences between 0.05 J/cm2 < F < 0.30 J/cm2, dirt ablation takes place without any contribution from the substrate. Results show that the main components of the dirt are fine particles of Fe mostly homogeneously distributed in a thin layer of grease and soaps. In the primary stages of the manufacturing process carbon residuals can also be found. By measuring light emission from the λ = 495.9 nm line of Fe(I) after laser ablation, we developed a real-time on-line method for the determination of the concentration of iron particles present in the surface dirt. The obtained results open new possibilities in the design of real-time instruments for industrial applications as a quality control of products and processes.

The photophysics of nitrocarbazoles studied by using spectroscopic, photoacoustic and luminescence techniques

The photophysical behaviour of 1-nitrocarbazol and 3-nitrocarbazol in different organic solvents has been studied by using spectroscopic, luminescence and photoacoustic techniques. Absorption spectra and triplet state transient spectra were recorded and formation quantum yields and lifetimes determined. Phosphorescence emission at 77 K and laser induced luminescence in acetonitrile solution at 298 K for the nitrocarbazoles were studied. Results are discussed in terms of the optimized structure of 1-nitrocarbazole and 3-nitrocarbazole and compared with that of carbazole. The nitro group attached to the carbazole moiety induces important changes in the photophysical behavior of those compounds.

Surface treatment analyses of car bearings by using laser-induced breakdown spectroscopy.

Determination of surface coating composition is a problem of great importance for industry and production related to the quality control of products and processes. One of the most outstanding aspects of laser-induced breakdown spectroscopy (LIBS) is its unique ability to carry out real-time depth profile analysis. This allows, for instance, the identification of layered coatings composition. In this work we performed depth profile analysis using LIBS to determine the composition of layered surface treatments of car bearings. Laser ablation thresholds for each coating layer were determined by acoustic measurements. Transitions between the different coating layers were also identified by an acoustic method. We developed faster and simpler semi-quantitative procedures to determine the relative composition of alloy surface coatings of car bearings as well as the possibility to characterize in real time these treatments.

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.

New method for real-time surface cleanliness measurement

The measurement of the surface cleanliness is a problem of great importance in many industrial and technological processes. Existing methods are based on laboratory procedures, they are not performed in real time, they cannot be automated, and usually they are restricted to a small portion of the sample. In this work we describe a new method for real time measurement of the amount of dirt deposited on a surface. It relies in the ablation of the dirt film by means of a short laser pulse and the subsequent measurement of the sound emitted. The intensity of the sound results proportional with the amount of dirt and provides a direct measurement of the cleanliness of the surface. The method requires a reference for calibration that was developed based in a uniform distribution of points printed on white paper or a transparent film. The point size and density can be easily modified providing a homogeneous, uniform and reproducible standard for the total amount of dirt measurement. Based on this method, we designed patented (P000101241-Argentina and 6.546.784 EEUU) and developed the first industrial instrument (ELMES) for on-line determination of the cleanliness degree of manufactured cold rolled steel plate bobbins.

Cleaning and characterization of objects of cultural value by laser ablation

Surface ablation with nanosecond laser pulses was applied to preservation, cleaning and compositional identification of objects of cultural value. On one hand, treatments of fabrics, coins, bones, and other archeological objects are shown, as well as applications to the preservation of covers, front of books and old manuscripts made in rag paper. Damage fluence thresholds for 17 different XIXth century types of papers, made by processing textiles, were determined. On the other hand, we use the spectroscopic analysis of the plasma generated as a result of laser ablation (LIBS- laser Induced Breakdown Spectroscopy-) for the determination of the elementary composition of unique pieces in anthropology and archaeology. In particular, we show applications to the identification of trace elements in Hominide teeth, of interest concerning the analysis of eating habits. We also apply LIBS to the determination of the composition of acheological objects belonging to different pre-Columbian cultures.

Volume and enthalpy changes of peroxodiphosphate dissociation

Abstract Photoacoustic measurements as a function of temperature in the range (294.1–308.2) K were used to determine the enthalpy and volume changes for the photoinduced dissociation at 266 nm of peroxodiphosphate ions in water. The analysis of the data, which considered the temperature dependence of the photodissociation quantum yield and of the thermoelastic parameters of the medium, yielded enthalpy and volume changes of (77±18) kJ mol −1 and (12±1) ml mol −1 , respectively. These values are compared with those reported for other systems.