Nanosecond transmission to total internal reflection switching has been demonstrated using a thin absorbing film of carbon microparticles suspended in ethanol. The switching results from laser‐induced cavitation and the large refractive index mismatch that occurs when the vapor bubble meets the surrounding glass substrate. This extraordinarily large refractive index change (≳0.3) causes the incident beam to be totally internally reflected at the glass‐vapor interface. Switching energies below 1 &mgr;J have been measured using a 5 ns doubled Nd:YAG laser (&lgr;=0.532 &mgr;m) pulse. We have investigated the effects that particle concentration, film thickness, and bias temperature have on switching performance.