Spectroscopic and lasing characterisation of a luminescent phenylene/bipyridine polymer

The luminescent polymer, poly[2,2′-bipyridine-5,5′-diyl-(2,5-dihexyl-1,4-phenylene)] (abbreviated PPBpy) dissolved in tetrachloroethane (TCE) and as neat film is characterised by optical absorption and emission spectroscopy. The absorption and stimulated emission cross-section spectra, the fluorescence quantum distributions, fluorescence quantum yields, degrees of fluorescence polarisation, and fluorescence lifetimes are determined. A lasing characterisation is carried out by pumping with single second harmonic pulses of a mode-locked ruby laser (wavelength 347.15 nm, duration 35 ps). The excited-state absorption at the pump-laser wavelength is determined by saturable absorption measurements. Laser oscillation of the polymer in TCE in an uncoated rectangular cell was achieved by transverse pumping using the cell windows for light feedback. From the laser threshold pump pulse energy density the effective stimulated emission cross-section at the lasing wavelength is extracted. The travelling-wave lasing behaviour of the polymer as neat film is studied by analysis of the amplification of the transverse pumped spontaneous emission. Surface emitting distributed-feedback lasing was achieved with a neat film on corrugated second-order periodic gratings.