The tell-tale signature of most lasers used in everyday applicationsfrom bar-code scanners to pen-size pointersis a bright red glow. The color is determined by the light's wavelength, and most lasers emit at only one wavelength. Now a new report published in the current issue of the journal Nature describes a light source measuring only tens of millimeters across that changes color according to temperature.

To make the new laser, Diederik Wiersma and Stefano Cavalieri of the European Laboratory for Non-linear Spectroscopy in Florence, Italy, manipulated the properties of a so-called random laser. Random lasers use light-diffusing materialoften in the form of a fine powderto trap light within the system long enough for amplification to occur. The more the light scatters, the larger the overall gain of the laser.

The researchers placed a liquid crystal inside a random laser source. By heating the crystal and changing the arrangement of its atoms, they could control the amount of light scattering within the laser and hence the color of emitted light. This so-called tunable random laser, the authors conclude, may one day find application as a source in active displays and temperature-sensitive screens or as a remote temperature-sensing device.