Opt. Express. 21, 11368–11375 (2013)

Optofluidic dye lasers, although attractive as miniature coherent light sources for integrated optics, unfortunately require a solvent for the preparation of their liquid dye solution. To fabricate such a laser without a solvent, Eun Young Choi and co-workers from South Korea and France used a liquid organic semiconducting material — liquid carbazole (9-(2-ethylhexyl)carbazole) — as the gain medium. They doped the liquid with green- and red-emitting laser dyes and incorporated it into two different laser geometries: waveguide and Fabry–Pérot microcavity lasers. The researchers observed amplified spontaneous emission and lasing when optically pumping the devices using ultraviolet light (355 nm) from the third harmonic of an Nd:YAG laser. This emission is thought to be due to cascaded Förster-type energy transfer from the liquid carbazole to the laser dyes. The emission wavelength could be tuned by using different liquid blends. In the case of liquid carbazole doped with green dyes in a Fabry–Pérot cavity, the laser thresholds were as low as 33 μJ cm−2 and 19 μJ cm−2 for emission wavelengths of 512 nm and 526 nm, respectively. This is comparable to the performance of organic solid-state dye lasers. The researchers anticipate that new liquid organic optoelectronics applications should be possible by using these tunable solvent-free fluidic organic lasers.