Development of photoacoustic spectroscopic technique for the study of materials

Recently, photoacoustic spectroscopy (PAS) technique has emerged as a valuable tool for the study of materials like biological, chemical and even geological materials. The suitability of photoacoustic (PA) technique lies in the fact that it can be applied irrespective of the physical state of materials i.e. solids, semisolid, liquid, gel, suspensions, etc. By realizing the importance of this technique we have considered worthwhile to set up this technique in laser and spectroscopy laboratory. The present work demonstrates the experimental set up for PAS, which consists of indigenous PA cell, 500 W halogen lamp/He–Ne laser, 1/8 m monochromator, chopper, and lock-in-amplifier. The performance of the newly fabricated PA cell is tested by parametric study using carbon black as a sample. The effect of chopping frequency on PA signal and phase angle is studied by recording the PA signal at different chopping frequencies (10–350 Hz). The effect of backing material on PA signal is studied by recording the PA signal of carbon black sample at different chopping frequencies for different backing materials (like wood, glass, silver, aluminium, etc). We have also studied the effect of particle size on PA signal by using bituminous coal of different particle sizes.