Effect of pulse repetition rate and number of pulses in the analysis of polypropylene and high density polyethylene by nanosecond infrared laser induced breakdown spectroscopy

Pulse repetition rates and the number of laser pulses are among the most important parameters that do affect the analysis of solid materials by laser induced breakdown spectroscopy, and the knowledge of their effects is of fundamental importance for suggesting analytical strategies when dealing with laser ablation processes of polymers. In this contribution, the influence of these parameters in the ablated mass and in the features of craters was evaluated in polypropylene and high density polyethylene plates containing pigment-based PbCrO4. Surface characterization and craters profile were carried out by perfilometry and scanning electron microscopy. Area, volume and profile of craters were obtained using Taylor Map software. A laser induced breakdown spectroscopy system consisted of a Q-Switched Nd:YAG laser (1064 nm, 5 ns) and an Echelle spectrometer equipped with ICCD detector were used. The evaluated operating conditions consisted of 10, 25 and 50 laser pulses at 1, 5 and 10 Hz, 250 mJ/pulse (85 J cm(-2)), 2 mu s delay time and 6 mu s integration time gate. Differences in the topographical features among craters of both polymers were observed. The decrease in the repetition rate resulted in irregular craters and formation of edges, especially in polypropylene sample. The differences in the topographical features and ablated masses were attributed to the influence of the degree of crystallinity, crystalline melting temperature and glass transition temperature in the ablation process of the high density polyethylene and polypropylene. It was also observed that the intensities of chromium and lead emission signals obtained at 10 Hz were two times higher than at 5 Hz by keeping the number of laser pulses constant. (C) 2011 Elsevier B. V. All rights reserved.

Effects of laser focusing and fluence on the analysis of pellets of plant materials by laser-induced breakdown spectroscopy

The effects of laser focusing and fluence on LIBS analysis of pellets of plant leaves was evaluated. A Q-switched Nd:YAG laser (5ns, 10Hz, 1064nm) was used and the emission signals were collected by lenses into an optical fiber coupled to a spectrometer with Echelle optics and ICCD. Data were acquired from the accumulation of 20 laser pulses at 2.0 mu s delay and 5.0 mu s integration time gate. The emission signal intensities increased with both laser fluence and spot size. Higher sensitivities for Ca, K, Mg, P, Al, B, Cu, Fe, Mn, and Zn determinations were observed for fluences in the range from 25 to 60Jcm(-2). Coefficients of variation of site-to-site measurements were generally lower than 10% (n=30 sites, 20 laser pulses/site) for a fluence of 50Jcm(-2) and 750 mu m spot size. For most elements, there is an indication that accuracy is improved with higher fluences. (C) 2012 Elsevier B.V. All rights reserved.

Femtosecond laser induced synthesis of Au nanoparticles mediated by chitosan

This paper reports the synthesis of Au nanoparticles by 30-fs pulses irradiation of a sample containing HAuCl4 and chitosan, a biopolymer used as reducing agent and stabilizer. We observed that it is a multi-photon induced process, with a threshold irradiance of 3.8 x 10(11) W/cm(2) at 790 nm. By transmission electron microscopy we observed nanoparticles from 8 to 50 nm with distinct shapes. Infrared spectroscopy indicated that the reduction of gold and consequent production of nanoparticles is related to the fs-pulse induced oxidation of hydroxyl to carbonyl groups in chitosan. (C) 2011 Optical Society of America

Discrimination of Basal Cell Carcinoma and Melanoma from Normal Skin Biopsies in Vitro Through Raman Spectroscopy and Principal Component Analysis

Objective: Raman spectroscopy has been employed to discriminate between malignant (basal cell carcinoma [BCC] and melanoma [MEL]) and normal (N) skin tissues in vitro, aimed at developing a method for cancer diagnosis. Background data: Raman spectroscopy is an analytical tool that could be used to diagnose skin cancer rapidly and noninvasively. Methods: Skin biopsy fragments of similar to 2 mm(2) from excisional surgeries were scanned through a Raman spectrometer (830 nm excitation wavelength, 50 to 200 mW of power, and 20 sec exposure time) coupled to a fiber optic Raman probe. Principal component analysis (PCA) and Euclidean distance were employed to develop a discrimination model to classify samples according to histopathology. In this model, we used a set of 145 spectra from N (30 spectra), BCC (96 spectra), and MEL (19 spectra) skin tissues. Results: We demonstrated that principal components (PCs) 1 to 4 accounted for 95.4% of all spectral variation. These PCs have been spectrally correlated to the biochemicals present in tissues, such as proteins, lipids, and melanin. The scores of PC2 and PC3 revealed statistically significant differences among N, BCC, and MEL (ANOVA, p < 0.05) and were used in the discrimination model. A total of 28 out of 30 spectra were correctly diagnosed as N, 93 out of 96 as BCC, and 13 out of 19 as MEL, with an overall accuracy of 92.4%. Conclusions: This discrimination model based on PCA and Euclidean distance could differentiate N from malignant (BCC and MEL) with high sensitivity and specificity.

Fluorescence spectroscopy as a tool to detect and evaluate glucocorticoid-induced skin atrophy

Topical glucocorticoid (GC) therapy has been successfully used in the treatment of several common cutaneous diseases in clinical practice for a long time, and skin atrophy is one of the most typical cutaneous side effects of this therapy. The aim of this study was to evaluate the potential of noninvasive fluorescence spectroscopy (FS) technique in the detection and classification of GC-induced skin atrophy. A total of 20 male Wistar rats were used in the experimental protocol under controlled environmental conditions and with free access to food. One group received topical application of clobetasol propionate 0.05% for 14 days to induce cutaneous atrophy (atrophic group) and the other (control) group received only vehicle application following the same protocol and schedule. Histological analyses and FS measurements with laser excitation at both 532 nm and 408 nm were obtained on days 1 and 15. The FS results were classified as "normal" or "atrophic" according by histological analysis. Fluorescence spectra obtained with excitation at 408 nm allowed a clear distinction between the control and atrophic groups, and were more informative than the those obtained at 532 nm. Our results reveal that, if correctly applied, FS allows noninvasive evaluation of corticosteroid-induced skin atrophy, and thus represents an important step towards better monitoring of undesirable side effects of cutaneous therapy.

FTIR and SEM analysis of CO2 laser irradiated human enamel

Objectives: Considering the enamel chemical structure, especially carbonate band, which has a major role in the caries prevention, the objective of the present study was to assess the chemical alterations on the enamel irradiated with CO2 laser by means of FTIR spectroscopy and SEM analysis. Design: The enamel surfaces were analysed on a spectrometer for acquisition of the absorption spectrum relative to the chemical composition of the control sample. The irradiation was conducted with a 10.6-mu m CO2 laser (0.55 W, 660 W/cm(2)). The carbonate absorption band at 1600-1291 cm(-1) as well as the water absorption band at 3793-2652 cm(-1) was measured in each sample after the irradiation. The water band was measured again 24-h after the irradiation. The band area of each chemical compound was delimited, the background was subtracted, and the area under each band was integrated. Each area was normalized by the phosphate band (1190-702 cm(-1)). Results: There was a statistically significant decrease (p < 0.05) in the water content after irradiation (control: 0.184 +/- 0.04; irradiated: 0.078 +/- 0.026), which increased again after rehydration (0.145 +/- 0.038). The carbonate/phosphate ratio was measured initially (0.112 +/- 0.029) and its reduction after irradiation indicated the carbonate loss (0.088 +/- 0.014) (p < 0.05). Conclusion: The 10.6-mu m CO2 laser irradiation diminishes the carbonate and water contents in the enamel after irradiation. (C) 2012 Elsevier Ltd. All rights reserved.

Polymorphic-induced transformations in CaTa2O6 single-crystal fibers obtained by laser-heated pedestal growth

Calcium tantalite (CaTa2O6) single crystal fibers were obtained by the laser-heated pedestal growth method (LHPG). At room temperature, this material can present three polymorphic modifications. The rapid crystallization inherent to the LHPG method produced samples within the Pm3 space group, with some chemical disorder. In order to check for polymorphic-induced transformations, the CaTa2O6 fibers have been submitted to different thermal treatments and investigated by micro-Raman spectroscopy. For short annealing times (15 min) at 1200 °C, the cubic modification was maintained, though with an improved crystalline quality, as evidenced by the enhanced inelastic scattered intensity (by ca. 250%) and narrowing of Raman bands. The polarized Raman spectra respected very well the predicted symmetries and the selection rules for this cubic modification. On the other hand, long annealing times (24 h) at 1200 °C led to a complete (irreversible) polymorphic transformation. The Raman bands became still more intense (ca. 15 times larger than for the as-grown fibers), narrower, and several new modes appeared. Also, the spectra became unpolarized, demonstrating a polycrystalline nature of the transformed crystals. The observed Raman modes could be fully assigned to an orthorhombic modification of CaTa2O6 belonging to the Pnma space group.