DETERMINATION OF THERMAlAND OPTICAl PARAMETERS OF lASER DYES USING PHOTOACOUSTIC SPECTROSCOPY

Abstract

Photoacoustic spectroscopy (PAS) is a powerful technique for the study of optical absorption spectra of solid and liquid samples directly through dtection of heat generated within the sample due to non-radiative relaxation processes. The basic idea of the method is the production of acoustic signal from a sample in a closed cell containing a gas (air) and a sensitive microphone when it is illuminated with a chopped light..

we• have employed the PAS to study the optical and thermal properties of the organic laser dye crystal violet (CV) in powder and liquid forms. A complete theoretical treatment of the PAS technique is presented which includes : 1 - The solution of the heat diffusion equation in the sample and surrounding media (by separation of variables method as RG) using the incident beam (front illumination) as the source term for the heat diffusion equation.

2 - The temperature distribution within the PA cell and the production of the PA signal.

3 - Separation of the PA signal into the two measurable quantities amplitude and phase which are complicated expressions and can be simplified in case of thermally thick samples.

4 - The PA signal for rear surface illumination which is used to measure thermal parameters of optically opaque samples.

The experimental set-up of the PA spectrometer has been. extensively described.