Random laser is tuned by heat

17 Jun 2002

Changes in temperature tune the emission from a cavity-less random laser.

Lasing sample

The first ever random laser that uses liquid crystals to tune its emission has been developed by researchers at the University of Florence, Italy (Nature 414 708).

In a random laser, multiple random scattering between particles in a disordered material is used instead of the mirrored cavity found in standard lasers. This results in light emission in all directions and means the laser can be also be miniaturized.

To make their tunable random laser, Diederik Wiersma and Stefano Cavalieri from the European Laboratory of Non-Linear Spectroscopy (LENS), used a ground glass powder as the scattering medium; a laser dye to provide gain; and a temperature-sensitive liquid crystal material to give tunability.

They pressed the powder into a slab and filled the spaces between the particles with the liquid crystal and laser dye. A frequency doubled Nd:YAG laser working in single shot operation is used to pump the random laser which itself has a typical output power of 1 µJ per pulse at 610 nm.

The light bounces randomly between the glass particles long enough to provide amplification and laser light to be emitted in all directions. With changing temperature, the liquid crystal changes phase (and its refractive index) enabling a measurable change in the amount of scattering within the material.

Wiersma told Optics Org: "At low temperatures - approximately 35°C - there is random laser action (the spectrum narrowed by up to a factor of 5) but at higher temperatures such as 75°C the random laser is below its threshold and we see a broad spectrum."

This novel laser has many applications. For example, it could be used as a pixel in a temperature-sensitive display or as a miniature remote temperature sensor because it can be designed to lase at a specific temperature.