The effect of laser pulse width on the efficiency of nonphotochemical laser-induced nucleation (NPLIN) of supersaturated aqueous solutions of KCl has been studied. At equivalent peak-power densities it was observed that the same fractions of samples were nucleated for both short (6 ns) and long (200 ns) near-infrared laser pulses. The results show that the efficiency depends on the peak-power density and not on the duration, or total energy, of the laser pulses. It is concluded that the mechanism is unlikely to be based solely on diffusion of solute to a sub-critical cluster. © 2009 Elsevier B.V. All rights reserved.