Jorge O. Tocho

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.

The luminescent quantum efficiency of Cr3+ ions in Cs2NaAlF6 single crystals

Abstract The luminescent quantum efficiency of Cr3+ ions in single fluoride crystal Cs2NaAlF6 was determined by using the simultaneous multiple-wavelength photoacoustic and luminescent experiments method, based on the generation of photoacoustic and luminescence signals after pulsed laser excitation. The luminescent quantum yield for the most important transition between the 4 T 2 → 4 A 2 vibronic levels was found to be 68±3%. This value agrees with that obtained from the ratio of the lifetimes of the corresponding transition at different temperatures.Abstract The luminescent quantum efficiency of Cr3+ ions in single fluoride crystal Cs2NaAlF6 was determined by using the simultaneous multiple-wavelength photoacoustic and luminescent experiments method, based on the generation of photoacoustic and luminescence signals after pulsed laser excitation. The luminescent quantum yield for the most important transition between the 4 T 2 → 4 A 2 vibronic levels was found to be 68±3%. This value agrees with that obtained from the ratio of the lifetimes of the corresponding transition at different temperatures.

Electron-lattice coupling in congruent Co-doped LiNbO3:Cr3+:ZnO crystal

The importance of the role of the ion-lattice coupling in determining the energy levels of Cr3+ ions in congruent LiNbO3 crystals doped with 2.9% of ZnO is demonstrated in this paper. The Racah parameters: B = 533 cm-1, C = 3244 cm-1 and the crystal-field intensity Dq = 1527 cm-1 were determined and the Tanabe-Sugano diagram was constructed. The characteristics of the absorption and the emission spectra of Cr3+ ions in these crystals can be explained in terms of the configurational-coordinate diagram in the harmonic approximation, with good agreement obtained. The Huang-Rhys parameter S = 6.86 and the lattice phonon energy ω = 343 cm-1 are also reported in this work.

Sizing particles used in the leather industry by light scattering

Three optical methods for sizing polymer particles are instrumented to be used in the leather industry. One method is based on the measurement of the light scattered intensity for several angles, and the other two are monochromatic or spectral extinction methods. Uniform latex particles and two commercial products used in leather finishing are measured. Advantages compared with electronic microscopy are discussed.

Influence of the electron-lattice coupling for Cr3+ ions in Nb5+ site into congruent co-doped LiNbO3: Cr3+: ZnO crystal

Abstract This paper shows the important role that plays the electron-lattice coupling to represent correctly the energy levels of Cr3+ ions in Nb5+ site into congruent LiNbO3 crystals doped with 5.3% of ZnO. Racahs parameters: B=646 cm −1 , C=3022 cm −1 and crystal field intensity Dq =1342 cm −1 were determined and the Tanabe–Suganos diagram was constructed. The characteristics of the absorption and emission spectra of Cr3+ ions in Nb5+ site have been explained in terms of the Configurational Co-ordinate model in the harmonic approximation. Huang–Rhys parameter, S=3.5 and the breathing phonon energy, ℏω=460 cm −1 , are also reported in this work. Different values of breathing phonon for Cr3+ in Nb5+ site than in Li+ site could explain the higher luminescent quantum efficiency of Cr3+ ions located in Nb5+ site in LiNbO3 crystals.

Relaxation processes of singlet excited state of 3,3′-diethyloxadicarbocyanine iodide (DODCI) photoisomer

Abstract Fluorescence induced by laser excitation was used in the study of the deactivation processes of excited states of both isomeric forms of 3,3′-diethyloxadicarbocyanine iodide (DODCI). Connection between excited states was analyzed by a two-step excitation method, and no evidence of a direct connection between them was found at low concentrations. This technique allowed us to obtain a normal fluorescence free photoisomer spectrum for the first time. Using cw excitation, saturated fluorescence spectra were interpreted on the basis of a photochromic system involving normal and photoisomer ground states and excited singlet states. A similar one-dimensional barrier picture is obtained, comparing the results with the direct photoisomerization process.

The extent of the ozone hole over South America during the spring of 1993, 1994 and 1995

The evolution of the total ozone measured by a network of ground stations located in Argentina and Chile between latitudes 53S and 33S during the spring of 1993, 1994 and 1995 is given. Ozone data obtained from the ground stations are compared with total ozone values supplied by the satellite showing a very good agreement. Ground station data were taken with a very low cost detection system based on differential optical absorption techniques under specific conditions. Several ozone depletion events were detected in the south of Argentina and Chile during those time intervals, even at latitudes as low as 33S. Potential vorticity maps obtained for those events indicate that the ozone depletions observed have an Antarctic origin.

Spectroscopic analysis of the crossed field excited C3 IIu-B3 IIg (0-0) UV laser band of N2 at low temperature

A liquid air refrigerated crossed field stimulated emitter was constructed to observe the 0-0 UV (337,1 nm) laser band of molecular nitrogen. The spectral analysis clearly showed that only one of the Λ-doublets were observed. The Λ-doublet components belong to two different Fortrat parabolas. This result allows a critical discussion of previous publications on the same subject.

Alternative method for concentration retrieval in differential optical absorption spectroscopy atmospheric-gas pollutant measurements

Differential optical absorption spectroscopy is a widely used technique for open-column atmospheric-gas pollution monitoring. The concentration retrieval is based on the fitting of the measured differential absorbance through the Lambert-Beer law. We present an alternative method for calculating the gas concentration on the basis of the proportionality between differential absorbance and differential absorption cross section of the gas under study. The method can be used on its own for single-component analysis or as a complement to the standard technique in multicomponent cases. The performance of the method for the case of cross interference between two gases is analyzed. The procedure can be used with differential absorption cross sections measured in the laboratory or taken from the literature. In addition, the method provides a criterion to discriminate against different species having absorption features in the same wavelength range.

Relaxation of induced dichroism in corona-poled doped polymers

Measurement of optical absorbance is used to study the re- laxation of acrylic film doped with Disperse Red 1 and poled with an electric field produced by the corona effect. Time variation of dichroism is studied over 10 days and results are adjusted with different time func- tions. Second-harmonic generation is presented as a test of the lack of symmetry of the poled film resulting from the orientation process. Subject terms: nonlinear optical materials; corona-poled polymer films; induced dichroism; time relaxation; second-harmonic generations.