Single Pulse, Single Crystal Laser-Induced Nucleation of Potassium Chloride

Abstract

The nonphotochemical laser-induced nucleation of aqueous supersaturated solutions of potassium chloride is demonstrated. We have observed that a single, 7 ns pulse of near-infrared (1064 nm) laser light can be used to grow a single crystal of potassium chloride. The experimental results are analyzed using a model in which nucleation is enhanced through the isotropic electronic polarization of subcritical crystal nuclei by laser radiation and the associated reduction in free energy of the nuclei. Classical nucleation theory is used to calculate the fraction of subcritical nuclei, initially in zero field, which become supercritical in the laser field; this fraction is correlated with the crystallization yield and is shown to successfully describe the dependences of the experimentally observed yields upon laser power and supersaturation. The experimental results are analyzed to obtain a phenomenological value of the crystal-solution interfacial tension, γ ) 2.19 ( 0.03 mJ m -2 .

A phenomenological theory of nonphotochemical laser induced nucleation

“…Samples were exposed to numerous laser pulses (except for single pulse exposure in Ref. 6) and, typically, less than half of the samples crystallized when irradiated even at the maximum intensity.Earlier proposed mechanisms based on the Kerr effect [1] or isotropic atomic polarizability of dielectric clusters [6] provided coherent qualitative features but were shown to produce effects on the order of only 10 −4 kT , five orders of magnitude below the observations.Here, we propose a phenomenological theory that shows how NPLIN evolves through nucleation of shortlived, progenitor metallic particles under strong electric field. The metallic particles have gigantic electronic susceptibility compared to dielectric substances and plasma frequency much higher than the laser frequency, thereby allowing the polarization to adiabatically follow the oscillating laser field.…”

“…Earlier proposed mechanisms based on the Kerr effect [1] or isotropic atomic polarizability of dielectric clusters [6] provided coherent qualitative features but were shown to produce effects on the order of only 10 −4 kT , five orders of magnitude below the observations.…”

“…For our purposes, the most important results are that: i) the field reduces the nucleation time by 13 orders of magnitude or even larger; and ii) it can do so at optical frequencies (∼ 10 14 Hz). Other observations include the existence of a threshold field, below which nucleation did not occur, and a linear type correlation between the cumulative fraction of samples nucleated and laser intensity [2,6], as well as the solute supersaturation [6].The anomalous strength of the observed field effect can be conveniently expressed in the terms of nucleation barrier W 0 that determines the nucleus induction time, τ = τ 0 exp (W 0 /kT ). Here, τ 0 > ∼ 10 −13 s is the characteristic atomic vibration or diffusion time, k is Boltzmann's constant, and T is temperature.…”

“…Samples were exposed to numerous laser pulses (except for single pulse exposure in Ref. 6) and, typically, less than half of the samples crystallized when irradiated even at the maximum intensity.…”

Supersaturation dependence of glycine polymorphism using laser-induced nucleation, sonocrystallization and nucleation by mechanical shock

“…30,31 Nucleation can be effected with a single laser pulse. 32,33 Typically the beam is not focussed tightly, so as to avoid optical breakdown or photochemical effects. 34 In experiments involving trapping, a CW laser beam is focussed tightly into a solution or at a solution interface.…”