Photoacoustic studies of glassing processes of metacrylate polymers

The glass transition in acrylate polymers was studied using photoacoustic signals induced by a Nd:YAG pulsed laser. The transition temperature was obtained by an analysis of the amplitude and time dependence of the signal

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. © 1997 American Institute of Physics.Fil:Mesaros, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Martínez, O.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Bilmes, G.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Simultaneous photoacoustic and luminescence multiple wavelength experiments

Fluorescence quantum efficiencies in solid and liquid materials were determined by simultaneous photoacoustic and luminescence experiments after excitation at several wavelengths, with at least one of them connecting a relaxation of known quantum efficiency. Results for Eu2+ in alkaline halide, Cr3+ in LiNbO3, and a cyanine in ethanol solutions, are given

Photophysical characterization of a photochromic system: The case of merocyanine 540

The fluorescence emission of merocyanine 540 (MC540) in 95% ethanol was studied under continuous irradiation. Fluorescence spectra from excited states of both normal (N) and photoisomeric (P) species are identical. The laser fluence dependence of the fluorescence intensity is interpreted on the basis of a photochromic system involving N and P ground states and first excited singlet states. Common flash photolysis equations are generalized in order to include a photoequilibrium between isomers. The emission data are used together with previous flash photolysis and optoacoustic results to obtain P fluorescence and photoisomerization quantum yields as 0.07 ± 0.02 and 0.20 ± 0.04, respectively, P absorption cross section at the maximum (560 nm) as 4.74 × 10-16 cm2 (125 × 103 M-1·cm-1), and the energy difference between the ground states as 165 kJ·mol-1. Internal conversion, which can take place as a direct process or through a twisted state, is the main deactivation pathway for excited singlet P. © 1990 American Chemical Society.Fil:Aramendía, P.F. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Excited state absorption in KCl : Eu2+

Non-linear behavior with respect to exciting fluence of both photoacoustic and luminescent signals in KCl : Eu(2+) excited by laser pulses at 355 nm, were analyzed in terms of excited state absorption (ESA). Measured ESA cross-sections for 355 and 420 nm were found to be 1x10-17 cm2 and 2.5x10-18 cm2 respectively

SITE SELECTIVE SPECTROSCOPY OF Nd3+ AND Cr3+ SITES IN LiNbO3 CRYSTALS CODOPED WITH Mg2+ IONS

The fluorescence properties of Nd3+ in Nd : MgO : LiNbO3 and Cr3+ in Cr : MgO : LiNbO3 systems have been systematically studied after site selective laser excitation. Three kinds of sites have been detected for the active (Nd3+ or Cr3+) ions. Two sites correspond to the active ion located in Li+ and Nb5+ lattice positions, and also appear in the singly (without MgO) doped systems. Codoping with Mg2+ ions induce the appearance of a new site for the active ion, together with a decreasing in the Li/Nb occupation ratio

Optical properties of Tm-doped LiNbO₃ and LiNbO₃(MgO)

The optical properties of Tm-doped LiNbO3 and LiNbO3:(MgO), especially within the 3H6 to 3H4 transition, have been studied. Differences in the absorption spectrum and particularly in the emission spectrum of Tm in both crystals are observed. New bands with different polarisation character appear in the MgO doped crystals, indicating the existence of Mg-perturbed Tm sites