One- and two-photon stimulated emission in oligothiophenes single crystals

We report on the observation of stimulated emission (SE) in plane-parallel single crystals of quaterthiophene (4T), sexithiophene (6T) and octithiophe ne (8T) at room temperature. One-photon transverse pumping at normal incide nce induces gain narrowing and leads to two SE lines emerging at respective ly low (50 mu J/cm(2)) and high (500 mu J/cm(2)) pumping levels. Two-photon excitation is realized in a longitudinal geometry, i.e. the near-IR beam o f a Ti:sapphire laser being directed parallel to the crystal faces. Intense and highly directional emission of visible light (green for 4T, orange for 6T and red for 8T) is generated along the pump pathway throughout the crys tal over lengths of several millimeters. Since in the solid state oligothio phenes also possess carrier mobilities as high as 0.1 cm(2)/V.s, they appea r as potential materials in view of an organic laser diode.