It has been demonstrated that a small change in the power of the trapping laser beam can be used to induce a small change in droplet absorption. This gives rise to a small shift in the droplet temperature and hence in the equilibrium size at a given relative humidity. The change in equilibrium droplet size allows the absorption coefficient along the pathlength of the laser beam to be determined. In the absorption studies it is the magnitude of the droplet size change necessary to re-establish equilibrium that is the important quantity to measure.