Inducing movement controls the emission of a random laser
Inducing movement controls the emission of a random laser lead image
Random lasers, in which the lasing medium consists of many randomly distributed scattering sites, are easy to fabricate but difficult to control. They promise to be cheaper than conventional lasers, but their emission tends to be erratic, with laser frequency, number of modes, and intensity exhibiting undesired fluctuations.
Several approaches have managed to tame aspects of these problems, but none had ever used the motion of the random laser itself as an experimental lever. Now, a technique reported in Applied Physics Letters uses the light-induced bending of a random laser to move it in and out of the focal plane of a pump laser, shifting the material above and below the lasing threshold.
The authors who developed this technique first prepared a 200-micron-thick strip of a composite material made from liquid crystal elastic polymer and titanium dioxide nanoparticles. They verified that the medium did, in fact, support lasing by measuring the spectral properties of the output light as they increased the energy provided by the pump laser. Finally, they introduced a continuous wave laser that caused the strip to bend, observing how the output spectrum changed.
As the material receded from the focal plane of the pump laser, the strongly peaked spectrum of the output light was replaced by ordinary fluorescence, indicating that the energy received from the pump had fallen below the lasing threshold. As the strip swung back into the pump laser’s path, the coherent light returned. The new design may “overcome typical issues such as quenching or heating of the random laser source and paves the way toward more advanced, self-actuating feedback mechanisms in these systems,” said Anjani Kumar Tiwari, an author of the paper.
Source: “Remote control of liquid crystal elastomer random laser using external stimuli,” by Anjani Kumar Tiwari, Lorenzo Pattelli, Renato Torre, and Diederik S. Wiersma, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5038663 .
