Instrumentation and Measurement Physics(DIMP)
Physique des instruments et mesures (DPIM)
M.L. BAESSO
Universidade Estadual de Maring, Brazil
Time resolved thermal lens for thermo-optical measurements in transparent materials during phase modification
The fortieth anniversary of the first observation of the thermal lens effect will occur in 2004 and certainly is a time for reflection on the contribution of this phenomenon to the study of transparent materials. As a troublesome effect during the operation of many lasers or as a high sensitive tool for non-destructive characterization of any kind of highly transparent samples, including solids, liquids and gases, the thermal lens spectrometry has provided substantial information regarding the thermo-optical properties of the studied materials. Measurements of the optical absorption coefficient, the temperature coefficients of refractive index and optical path length, the fluorescence quantum efficiency, the thermal diffusivity, the thermal conductivity, etc, have been performed. The evolution of the thermal lens methods for non-destructive studies has allowed new insights in recent years as a consequence of the introduction of several modifications in their experimental set up. Exploring the remote nature of the technique, several works have focused on the ability of the method to evaluate the samples during the temperature scanning, the application of external field and also during the occurrence of photochemical reaction. The aim of this presentation is to highlight the ability and the accuracy of the thermal lens method for spectroscopic measurements performed during the samples phase modification. Quantitative measurements during phase transitions in biomaterials, glass transitions in polymers and the photochemical reaction in Cr6+-complex solution will be discussed. The focus will be the resolution of the method as compared to conventional measurements. Finally, together with the new perspectives of future work, the recent improvement in the thermal lens data acquisition procedure will be discussed.