Optical gain and photophysics of organic materials for photonic applications

In this master thesis we analyze the photophysics and the optical properties of different conjugated polymers in order to achieve Amplified Spontaneous Emission (ASE) and lasing emission. Conjugated polymers are easy-processable low-cost materials whose optical properties can be tuned acting on their chemical structure and conformation. One of their main characteristics is the presence of high optical gain over a large spectral visible region; we will exploit this feature looking at ASE and lasing from solution or solid film. After a brief introduction (chapter 1) about the aim of the work, in chapter 2 we introduce the basic theory about conjugated organic polymers and the pump-probe experimental technique used in this work. In chapter 3, we show experimental results on ASE coming from a new co-polymer (called R1A) synthesized in the ISMAC laboratories in Milano. By means of pump-probe technique we study the photophysics of a drop cast film. Energy transfer between the two components of the co-polymer is resolved and modeled by mathematical fits. We observe a long-lived gain which allows us to successfully achieve ASE in the nanosecond timescale regime. In view of obtaining laser emission, in chapter 4 we look at a novel blend formed by a well known polymeric compound (Polyfluorene (PFO)) and a liquid crystal in its cholesteric phase (CLC). The idea is to use the CLC as a matrix able to create optical feedback for the PFO emission. We start with the study of the blend where the LC is in its nematic phase. We induce an alignment of the PFO chains showing a good mix between the two compounds. Going from the nematic to the cholesteric phase the LC induces a phase separation in the mix deleterious to achieve lasing emission. Finally, in chapter 5 we present ASE from an integrated optofluidic device based on PFO emission. We show that it is possible, adding an array of waveguides at the exit of a microchannel buried in a chip and full of the organic solution, to harvest the ASE coming from the solution and deliver it outside the optofluidic chip for further manipulations.