Organic materials for lasers

Organic photonics is a fast-growing field that focuses on phenomena and components in which photons interact with organic materials. The ability of organic materials to emit light very efficiently across the visible spectrum has long been known (dye lasers, organic fluorophores, etc.). However, the discovery in the early 1980s of organic semiconductors (which also have electrical charge transport properties) revolutionized the field, enabling the invention and development of new components such as solar cells and organic light-emitting diodes (OLEDs). These devices, now mature and available on the market, also benefit from the specific structural properties of organic materials, which enable them to be adapted to numerous functions through chemical engineering, as well as their ease of deposition and shaping on numerous substrates and large surfaces. This makes it possible to target low-cost applications that are difficult to access with inorganic technologies, such as large-scale "light sheets" and, in general, components that can be easily adapted to existing technologies.

Beyond these applications, this article focuses on the emission of coherent light by organic materials, in other words, lasers. Organic lasers have undergone intense development over the last two decades, and there is now a wide variety of materials available. Until 25 years ago, "organic laser" was synonymous with "dye laser", i.e. a laser whose gain medium is a liquid solution of π-conjugated molecules (DCM, rhodamine, etc.). The variety of molecules available, coupled with the fact that a given molecule has a very broad emission spectrum, then made them the only tunable lasers available, capable of covering the entire spectrum from near UV to near IR. Interest in liquid dye lasers began to wane in the 1990s, mainly for practical reasons: this type of laser is generally cumbersome and difficult to maintain (regular dye changes, alignment, etc.), and the dyes used and their solvents are often carcinogenic.

There are two main reasons for the renewed interest in lasers based on organic materials. Firstly, the emergence in the 2000s of all-solid-state systems based essentially on organic semiconductors means that "liquid" systems can be dispensed with, offering the prospect of compact, low-cost, mass-produced and widely tunable lasers. In addition, the possibility of injecting charges directly into an organic semiconductor makes it theoretically possible to produce an organic laser diode. However, in 2022, this field is still in its infancy. Organic lasers are still optically pumped. From this perspective, the other more recent advance (2010 to 2020) concerns the pumping system, with the arrival at maturity of high-power blue (or even UV) inorganic laser diodes. Here again, they offer several...