Collinear photothermal deflection spectroscopy with light-scattering samples.

An analytical model that incorporates effects of light scattering was developed for dual-beam photothermal deflection spectroscopy. Thermal gradients induced by a modulated excitation beam deflect an optical probe beam which was treated as being of finite dimensions. Mechanisms by which thermal gradients produce refractive index gradients are discussed, with an explicit expression for dn/dT being derived. Experimental studies with suspensions of small latex particles in Nd(3+) solutions demonstrated that the model accurately predicts both the shape of the deflection signal and the attenuation of the signal due to light scattering. The absolute magnitude of the observed signal is approximately predicted by theory.