Ultrafast organic lasers and solid-state amplifiers

Abstract

This thesis presents an investigation of the lasing dynamics and optical amplification devices using conjugated polymers. Spectroscopic studies of conjugated polymers and dendrimers were also performed. Conjugated polymers and dendrimers are materials with great potential as display materials and tuneable lasers due to their broad spectra and high optical gains. The effect of conjugation is studied in MEH-PPV and an anisotropy measurement of two different cored dendrimers has been shown to verify a theoretical prediction on their depolarisation. Singlet emission from a highly efficient phosphorescent dendrimer is also observed and is the first known report of fluorescence from this class of dendrimers. Conjugated polymers exhibit optical gain over broad spectral ranges, which has led to much interest in their potential as novel laser gain media. Investigations into lasing from conjugated polymers has been confined mainly to studying the lasing properties and not the temporal dynamics of the laser pulses. In this work an investigation into the lasing dynamics of a 2D-DFB conjugated polymer laser is demonstrated with the first subpicosecond laser pulses observed for a polymer laser. A novel encapsulated laser fabricated via a soft lithography route was also studied and exhibited laser pulse of 6 ps duration. The high gain observed over broad spectral ranges also means that these materials are suitable for use as optical amplifiers. Broadband gain in a conjugated polymer solution was demonstrated with a gain of 30 dB accessible across a 60 nm wavelength range. In the solid state the limited thickness of films (~ 100 nm) and the uneven nature of the film edges had limited the ability to study the amplification of a probe signal. The first practical solid state conjugated polymer amplifier has been demonstrated. The device uses grating structures to couple a probe signal into and out of the gain region. The gain dynamics of different length amplifiers were studied and an 18 dB gain was observed in a 300 µm device length using a conjugated polymer blend of RedF and F8BT. Further work on a conjugated polymer MEH-PPV led to a 21dB gain in a 1 mm device.