Simultaneous retrieval of optical gains, losses, and threshold in active waveguides

•An analytical expression to describe the growth of ASE intensity has been derived.•Many photophysical effects, including singlet-singlet annihilation, are assumed.•Gains, losses and threshold are simultaneously retrieved from a single experiment.•A graphical user interface has been developed to implement the methodology. The generation of Amplified Spontaneous Emission (ASE) is routinely used to assess the performance of active materials prior to developing thin film lasers. The Variable Stripe Length method has been profusely used for decades to measure the optical gain in these materials and devices, but experimental and theoretical evidences cast doubts upon its reliability. With the advent of an ever increasing number of solution-processed laser compounds that can be implemented as low-cost, flexible, and/or integrated devices, there is now more than ever a need to develop an alternative and trustful method to delineate all their amplifying signatures. Herein, a new formalism to fully characterize the ASE properties, based on the most frequent Variable Pump Intensity method, is reported. An analytical expression taking into account the most relevant spatiotemporal and photophysical effects has been found that can be fitted to ASE spectra. This expression allows retrieving, from a single ASE experiment, the spectrally resolved losses coefficient and net optical gains at all pump values, as well as to calculate, instead of visually finding, the ASE threshold. The reported formalism serves as a tool to categorize the best candidates for a given laser application through a reliable, robust, time-saver, and standardized methodology.