Focused laser beam interactions with methanol droplets: Effects of relative beam diameter

The effect of the local diameter of a focused CO₂laser beam on calculated internal source function distributions and experimentally observed explosive characteristics is examined for 165-μm spherical methanol droplets. Experimental results show that the location and the characteristics of the explosive process change as the droplet is moved out of the laser focal point along the axis of propagation. Theoretical calculations indicate that, when the beam diameter is of the same order of magnitude as the droplet diameter, a modification of Mie theory, accounting for the finite beam size of the laser, is necessary to provide results which are consistent with experimental observations.