Technical Papers and Presentations

Photothermal deflection spectroscopy (PDS) relies on the angular displacement of a probe beam through a fluid with varying index of refraction. The precise angular displacement of the probe beam is dependent on the entire index of refraction field, which is in turn dependent on fluid temperature. Typically, fluids with high thermo-optic coefficients are chosen so as to maximize the probe beam deflection and enhance signal. While some analytical models have been developed to estimate the angular deflection of the probe beam, those models require many assumptions that when compounded, offer only an estimation of probe beam deflection. It is therefore difficult to correlate the model with experiment. In this presentation, we will discuss using the Ray Optics Module in COMSOL Multiphysics^® simulation software to calculate the angular deflection of the probe beam, which offers flexibility in specifying experimental complexities that analytical models cannot accommodate. By replicating experimental geometries and material properties in COMSOL Multiphysics^®, we are able to infer index of refraction from temperature profiles of the thermal fluid solved using the Heat Transfer Module. Using COMSOL LiveLink™ for MATLAB^®
allows us to solve for the deflection of the probe beam for many different temperature and geometry profiles. Correlating these simulations with experiments allows for a precise calculation of the temperature of the fluid medium, which can be fractions of a degree Celsius.