Electrically Driven Tunable Organic Lasers May Be Feasible

Annie L. Fischer

Solid-state organic dye lasers that use multiple-prism grating-tunable laser oscillators require another laser as an excitation source. Now researchers at Eastman Kodak Co. in Rochester, N.Y., have reported spatially coherent emission and partially coherent spectral emission in the pulsed regime from an electrically excited tandem organic LED (OLED). According to research physicist Frank J. Duarte, the finding points toward the development of electrically excited, broadly tunable organic semiconductor lasers.

Two characteristics of laser radiation are low beam divergence and narrow linewidth. In this work, the group achieved divergence of 2.53 mrad and partial spectral coherence, which Duarte compared to the emission of a broadband laser such as a high-power dye laser, prior to the use of intracavity optics.

The researchers used coumarin 545T as the emission medium, which they doped into the Alq host in a tandem OLED structure. They achieved spatially coherent emission by using two spatial filters 10 to 13 cm apart. They found no fundamental limitations to eventually achieving tunable lasing with coumarin 545T in electrically excited semiconductors.

The spectral distribution from the doubly spatially filtered tandem OLED was comparable to that of an optically pumped high-power broadband dye laser. The next step is to look at the origins of this coherence and its relation to internal interferometric phenomena.

The researchers will explore possible laser behavior by using excitation at higher pulsed voltages in the nanosecond domain, which they expect will more closely reproduce the excitation characteristics of high-power dye lasers.