Nanoparticle Scattering Improves Laser Performance

Dr. Inmaculada Garcia-Moreno and her colleagues at theInstituto de Quimica-Fisica “Rocasolano” and the Instituto de Ciencia yTecnología de Polímeros in Madridhave shown that certain nanoparticles added to dye lasers can scatter light ina way that increases the efficiency of the material’s laser action as well asmake the materials easier to handle.

Lasers made from dyes can be tuned over a very broad visiblewavelength, from the near ultraviolet to the infrared. They can be pulsed athigh energy and are used for applications ranging from isotope separation andpollution monitoring to cancer therapies and tattoo removal. As the dyes usedare liquids it is often helpful if they can be incorporated into a solidmaterial. Organic polymer materials are usually used for this purpose, andinorganic particles are often added to improve the physical stability andhandling properties. Unfortunately, the inorganic additives usually havedetrimental effects on the optical properties of the composites, such astransparency and laser capabilities.

However, as the Spanish researchers have demonstrated, ifthe inorganic material comprises particles that are both small enough andrandomly enough distributed, then the transparency of the composites is notaffected and the emission from the dye is actually enhanced.

The chemistry that has made this possible is the use ofnanoparticles of polyhedral oligomeric silsesquioxane (POSS) for the inorganiccomponent. POSS is a silicon and oxygen-based material that can be readilyincorporated into an organic matrix. The nanoparticles were found to bedispersed on a molecular level. The physics behind the laser enhancement is aphenomenon known as “incoherent random laser”, in which the coherent lightemitted by the dye is scattered weakly by the POSS nanoparticles, causing it tohave an elongated path inside the material and providing extra feedback.

The researchers initially found it difficult to realize thata homogeneous material with nanoparticles in the range 0.5-4 nm could sustainscattering, but were able to show that not only did it occur, but that theeffect was independent of the type of dye molecules used and theirphotophysics. “Thus,” Dr. Garcia-Moreno claims, “dye-doped POSS solutions couldbe defined as a kind of universal gain media, overcoming the dye/hostspecificity that has been recognized as one of the greatest limitations ofthese laser systems.”

Other advantages include “the easy synthesis of thePOSS-based hybrid materials” and “their significantly improved physical,thermal, and optical properties as compared with the materials used up to nowfor incorporating lasing dyes”. The researchers therefore see the possibilityof using these new hybrid materials as alternative sources for optoelectronicdevices, competing with dendronized or grafted polymers. “The POSS-basedmaterials show the potential to bring to life a practical, commercial,easy-to-handle, and stable solid-state dye laser.”