Fragments of irradiated crystals.

Lithium niobate is an example of a photorefractive crystal -- one of a remarkable group of materials that can change their optical properties in response to the very light that passes through them. Widely used for fabricating devices that serve as the optical counterparts of transistors and switches, crystals of lithium niobate are now in great demand. But difficulties encountered in machining and processing the crystals by mechanical or chemical means, and uncertainties about their susceptibility to damage by high-intensity lasers, have persuaded researchers to examine more closely how lithium niobate responds to intense, ultraviolet laser light.

Kai Tang and his co-workers at Vanderbilt University in Nashville, Tenn., studied the effects of intense pulses from a xenon chloride laser focused on the polished surface of a lithium niobate crystal. Their experiments showed that such irradiation forced the ejection of many different types of atoms, ions and molecules, with the proportion of each chemical species dependent not only on the laser intensity, but also on whether a given spot had been previously irradiated.

In particular, the researchers discovered that low laser intensities generated significant amounts of neutral lithium niobate molecules. In principle, the resulting molecules could then be used for growing thin films of lithium niobate.