The dependence of the amplified spontaneous emission on the waveguide excitation length for high quantum efficiency conjugated polymers

The waveguide properties of high quantum efficiency thin film of poly(9,9-dioctyl-fluorene-2,7-diyl) conjugated polymer has been studied at room temperature. The analysis of the enhancement of the amplified spontaneous emission intensity at different excitation lengths has been performed based on the theoretical method developed by Silvestre et al. (2008) [20]. The increase in the threshold intensity with decreasing excitation length has been experimentally observed. This occurs as a response to the cavity gain in order to overcome the total losses when its length decreases, which represents an important factor to support the gain dependence on the excitation length. Even though highly efficient polymers can reach thresholds at relatively lower intensities because the losses are more easily overcome, the observed intensity behavior of the amplified spontaneous emission can only be explained assuming a gain dependence on the excitation length.

Graphical abstractAmplified spontaneous emission (ASE) threshold intensity is dependent upon the excitation length (open circles) of a PFO thin film waveguide (the dot-dashed curve is a guide for the eye). This dependence is a direct consequence of the dependence of gain on the excitation length which is a characteristic of low as well as of high gain polymer waveguides. The variation of the ASE threshold as a function of excitation length is related to the quantum efficiency of the luminescent material.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► ASE gain and threshold dependence on excitation length of PFO thin film waveguides. ► The ASE threshold of PFO increases 3-fold with decreasing excitation length. ► The variation of ASE threshold with the excitation length depends on the PLQY. ► Low and high gain polymers exhibit gain dependence upon excitation length.