Polarization independence of laser-induced nucleation in supersaturated aqueous urea solutions.

Yao Liu,Andrew J Alexander,Martin R Ward

doi:10.1039/c6cp07997k

Abstract

In a seminal report on laser-induced nucleation in aqueous supersaturated solutions (Phys. Rev. Lett., 1996, 77, 3475) it was noted that needle-shaped crystals of urea were aligned with the direction of the electric field of the linearly polarized laser pulse. The results gave rise to a new mechanism for control of crystal nucleation involving alignment of solute molecules (optical Kerr effect) now commonly known as non-photochemical laser-induced nucleation (NPLIN). Recent theoretical and experimental work has cast doubts on the optical Kerr effect mechanism. In the present letter we present results from digital imaging of urea-crystal growth immediately following laser-induced nucleation. Analysis of the data shows no statistically significant correlation between crystal angle and direction of linear polarization. The results overturn a long-held result that has shaped theoretical and experimental studies of NPLIN.

Highlights

Nucleation is of fundamental scientific interest and has significant economic value
The discovery of non-photochemical laser-induced nucleation (NPLIN) happened by chance, while Garetz et al had been looking for second-harmonic generation in aqueous solutions of urea.[6]
Since the observation of alignment of urea needles along the electric field of the light is central to understanding the mechanism, we have carried out digital imaging of crystal growth during NPLIN of urea

Summary

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Polarization independence of laser-induced nucleation in supersaturated aqueous urea solutions†. In a seminal report on laser-induced nucleation in aqueous supersaturated solutions Rev. Lett., 1996, 77, 3475) it was noted that needle-shaped crystals of urea were aligned with the direction of the electric field of the linearly polarized laser pulse. The results gave rise to a new mechanism for control of crystal nucleation involving alignment of solute molecules (optical Kerr effect) commonly known as non-photochemical laser-induced nucleation (NPLIN). Recent theoretical and experimental work has cast doubts on the optical Kerr effect mechanism. In the present letter we present results from digital imaging of urea-crystal growth immediately following laser-induced nucleation. The results overturn a long-held result that has shaped theoretical and experimental studies of NPLIN

Introduction

Experimental methods

Results and discussion