Photo-physical characterisation and travelling-wave lasing of some TPD-based polymer neat films

Abstract

Abstract Travelling-wave lasing (amplification of spontaneous emission) is reported for neat films of a series of five red, green and blue emitting TPD-based polymers, the TPD-phenylenevinylene and the TPD-xylylene copolymers. Thin samples on glass substrates were fabricated by spin-coating and transversally pumped with picosecond excitation pulses (wavelength 347.15 nm, duration 35 ps). Lasing occurs around 421, 536, 540, 571, and 618 nm with a line-width smaller than 10 nm. The threshold pump pulse energy densities are determined and found to be 60 μJ / cm 2 for the blue emitting non-conjugated polymer (Poly-TPD(4M)-DPX) and 6–8 μJ / cm 2 for the green and red emitting conjugated polymers TPD(4M)-MEH-PPV and TPD(4M)-MEH-M3EH-PPV. The laser output saturation at high excitation energy densities is studied. The length of effective amplification of spontaneous emission is approximately 1 mm. Effective stimulated emission cross-sections are derived from the pump pulse energy density dependent spectral narrowing of the amplified emission signals. The optical constants (absorption spectrum and refractive index spectrum) of the neat films are determined by reflection and transmission measurements. The absorption cross-section spectra are extracted. The fluorescence quantum efficiencies and the fluorescence lifetimes are measured.