Nonphotochemical laser-induced nucleation of potassium halides: effects of wavelength and temperature

Nonphotochemical laser-induced nucleation (NPLIN) of KCl and KBr has been studied using nanosecond laser pulses with wavelengths of 532 and 1064 nm. The ratio of the number of samples nucleated to the number irradiated with the laser (f) follows a nonlinear dependence on peak power density that approaches f = 1 at higher incident powers, which we fit with a Poisson function. The threshold power required to nucleate samples is lower at 532 than at 1064 nm, and we observe that a higher fraction of samples nucleate when exposed to 532 nm pulses at a given laser power. In comparison to KCl, we see higher fractions of KBr samples nucleate and lower threshold values at both wavelengths. Samples of KCl of equal supersaturation at two different temperatures (23 and 33 °C) shot with 1064 nm pulses show that the 33 °C samples are significantly more labile to nucleation. The ratio of samples nucleated at 33 °C compared to those at 23 °C was 2.11 ± 0.47. A classical nucleation model based on activation of subcritical clusters in solution accounts remarkably well for the experimental data and provides phenomenological values of the crystal–solution interfacial tension (γ) at 23 °C for KCl and KBr of 5.283 and 4.817 mJ m–2. At 33 °C, the model yields a best-fit value of γ = 5.429 mJ m–2 for KCl.