The fluence at the particle surface cannot be inferred immediately from the incident laser fluence, due to the important role of the light reflected from the mirror and interfering at the particle–MLD interface. Since the size of the Ti particles is much larger than the laser wavelength, ray tracing is suitable for optical modeling. Interference effects are expected to be significant only in the vicinity of the point of contact with the mirror, where the intensity is low. In fact, electromagnetic theory-based calculations using a finite-difference time-domain method in two-dimensions show that the contribution of interference to the absorption power of the Ti particle at the length scales studied is insignificant.19 To carry out the ray tracing, we employed the commercial application FRED (distributed by Photon Engineering, LLC, Tucson, Arizona), a multipurpose optics code widely used in optical design and analysis. We previously used this code in calculating laser interactions with composite materials22 and metal powders.23 Each ray travels from surface to surface, with a particular power in each polarization. At the surface of the particle, rays are absorbed and reflected according to the Fresnel absorptivity and reflectivity of Ti (index of refraction taken as ). The absorbed power is recorded, and only the reflected ray is followed. The absorptivity and reflectivity depend on both the angle of incidence and the polarization.