Laser threshold analysis of first and second order organic solid-state distributed feedback laser

Optically pumped organic semiconductor thin-films have been processed on first and second order distributed feedback gratings. The organic thin-films were made by co-evaporation of tris-(8-hydroxy quinoline)aluminium (Alq(3)) and the laser dye 4-(Dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran (DCM2). The DFB laser wavelength varied depending on the grating period between 647.8 nm and 668.6 nm for first order operation and between 626.7 nm and 640.1 nm for second order operation. By evaporating the same organic film on both resonator designs we could compare first and second order laser parameters. We measured laser output characteristics and determined threshold energy values for different wavelengths and for first and second order of the Bragg grating. The laser threshold energy of the first order organic DFB laser was reduced by a factor 8 compared to the second order laser. Minimum threshold energy density was measured for a first order sample with 13.8 muJ/cm(2). Reducing, the laser threshold value is especially important for future applications like electrically driven organic solid-state lasers, where it will be more difficult to reach the laser threshold excitation.