First photothermal deflection spectroscopy set-up in Egypt

Abstract

We have succeeded in carrying out some ultra-sensitive photothermal experiments, using photothermal deflection spectroscopy (PDS) (or mirage effect). We have also employed the PDS technique to study the optical and thermal properties of solid/air interfaces. The experimental set-up of the transverse PDS has been described. The experimental results show that there is an exponential decay in PD signals with increase in the chopper frequency as well as with an increase of the phase difference. The PD signal decreases with increasing the probe beam normal offset to allow us to calculate the thermal diffusion length of the deflection medium (air in our case). We determined the thermal diffusion of air to be = 0.43 mm at the chopper frequency 50 Hz, which is in agreement with published values. Further, we employed the PD technique to obtain the spectra for two dyes [Rhodamine 6G (Rh6G) and Crystal Violet (CV)] of different optical absorption structures. The PDS shows a good resolution of the peaks of CV which are hardly separated in optical absorption measurements. Finally, a comparison of the photoacoustic spectra (PAS) of the two dyes was carried out, which showed that PDS has better spatial spectral resolution. © 1993 Indian Academy of Sciences.