Bruce Garetz et al. [Phys. Rev. Lett. 77 (1996) 3475] describe in a 1996 paper, the discovery by accident of the phenomenon of non-photochemical laser induced nucleation (NPLIN). They had been shining laser light at supersaturated solution of urea to do some spectroscopy on the solution itself, and saw crystals had formed. A supersaturated solution is one that has much more solid dissolved than would be stable, but the extra stuff can stay dissolved for some amount of time.

We have recently been investigating this phenomenon in detail, and have demonstrated NPLIN for simple inorganic salts such as KCl in aqueous solution. We have shown that we can obtain a single crystal of KCl using a single laser pulse. The advantage to using KCl is that we have a better control over the nucleation conditions, and the system is also potentially more theoretically tractable. We have devised a model for our results based on classical nucleation theory, which has been modified to include a term dependent on the square of the electric field resulting from the stabilization of a dielectric particle immersed in a continuum solvent [1].

More recently, we have demonstrated both spatial and temporal control of crystal nucleation using a supersaturated solution of KCl, formed in an agarose gel (see picture opposite). We have used a simple optical mask, and raster scanned the laser across the gel. Crystals are only formed where the gel has been exposed to the pulses of near-infrared laser light [2].

This work has been featured in news articles in Chemical & Engineering News, and in Nature News.

Relevant publications:

1. A. J. Alexander, P. J. Camp, Cryst. Growth. Des. 9, 958 (2009) : "Single pulse, single crystal laser-induced nucleation of potassium chloride". doi:/10.1021/cg8007415
2. C. Duffus, P. J. Camp, A. J. Alexander, J. Am. Chem. Soc. (2009): "Spatial Control of Crystal Nucleation in Agarose Gel", ASAP communication. Link to reports in Chemical & Engineering News and Nature News.