A new nanoscale plasmon laser developed at Northwestern University changes color in real time through a process as simple as swapping one liquid dye for another. The scientists responsible for the technology claim this is the world's first liquid nanoscale laser, and it could find uses in medical diagnostics as well as military or security applications.

Unlike conventional lasers, which use mirrors to bounce light back and forth through a gain medium (kind of like an amplifier), this new nanolaser contains an array of reflective gold nanoparticles that accomplish the same feat on a considerably smaller scale. Previously-developed nanolasers used solid gain materials, which provide a fixed wavelength, but the Northwestern team used a liquid (more specifically, an organic dye) instead.

Liquid nanolasers have two big advantages. One is that they can be kept stable for a longer period of time because the liquid gain materials can be constantly replenished. The other is that their wavelength is tunable. To change the wavelength – which is to change the color – you need only change either the liquid dye (potentially big change) or the solvent that the dye is dissolved in (more moderate change), which are housed in a microfluidic channel above the laser’s cavity.

"We believe this work represents a conceptual and practical engineering advance for on-demand, reversible control of light from nanoscopic sources," said lead researcher Teri W. Odom.

Liquid nanolasers could led to new "lab on a chip" devices for medical diagnoses because their sensitivity is so great that they can enhance and detect weak physical and chemical processes as they occur on a nanoscale. Beyond that, they may be useful in optoelectronic integrated circuits and data storage.

A paper describing the research was published in the journal Nature Communications.