Polystyrene spheres enable wavelength control in random lasers

Random lasers consist of irregularly shaped material that scatters light and achieves optical-gain amplification, but not resonance or wavelength tunability. While random lasing has been successful using various powders, suspensions, or porous materials, scientists in Italy and Spain have shown that spherical polystyrene microspheres dubbed “photonic glass” enable resonant tunability even in completely random systems with no periodicity.

Researcher Diederik Wiersma at the European Laboratory for Nonlinear Spectroscopy (Florence, Italy) and team members at the Instituto de Ciencia de Materiales (Madrid, Spain) used randomly assembled monodisperse polystyrene spheres coated with laser dye as the scattering medium. They directed a frequency-doubled Q-switched Nd:YAG laser with a 10 Hz repetition rate into the photonic glass, which consisted of spheres ranging in diameter from 0.2 to 3 µm. Mie resonance occurred at wavelengths near the maximum of the gain curve. Wiersma and his team determined that control of the diameter and refractive index of the spheres alters the lasing wavelength, making it possible to select specific lasing modes. Random lasers with a controllable wavelength could have many applications ranging from medicine to laser fusion. Contact Diederik Wiersma at wiersma@lens.unifi.it.