Tunable efficient laser emission from electroluminescent functionalized oligothiophene

Summary form only given. While organic light emitting diodes (LEDs) have recently reached commercial figures, there is still a great effort to develop new organic gain materials with improved performances for plastic lasers. Functionalized oligothiophenes containing thienyl-S,S-dioxide groups are very appealing candidates for this purpose. Single mode laser action is obtained in neat films of this family of oligothiophenes, with stable external plane-concave resonators. The /spl sim/450-600 nm thick films were deposited by spin coating from chloroform solution, directly onto the plane mirror. The lasers were optically pumped in a longitudinal configuration by 180 fs laser pulses at 395 nm at 1 kHz repetition rate. The excitation beam was focused to a /spl sim/80 /spl mu/m spot size onto the films, to match the cavity mode (/spl sim/40 /spl mu/m spot size). Using quinquethiophene-S,S-dioxide we obtained laser emission tunable in a 30 nm wavelength range, around 607 nm, with a 5 mJ/cm/sup 2/ pump threshold. With a further modification of the material, in a cyclohexyle substituted thienyl-S, S-dioxide quinquethiophene, we obtained greatly improved performances. The input-output characteristic we obtained together with a numerical fit are shown; the emission grows linearly with energy excitation, as expected for laser action. The pump threshold is at 2 nJ, corresponding to a fluence of 10 /spl mu/J/cm/sup 2/. From this value we can estimate a current threshold of 10/sup 3/ A/cm/sup 2/ for electrical pumping. By changing the cavity length we could tune the laser emission wavelength from the yellow to the red. We obtained single mode laser emission, with almost the same output energy, in a 37 nm wavelength range from 575 to 612 nm.