Gain coefficient method for amplified spontaneous emission in thin waveguided film of a conjugated polymer

Abstract

A method based on the unidimensional gain equation has been developed in order to fit the experimental data due to amplification of spontaneous emission in a thin film of conjugated polymer waveguide. The results have confirmed not only a dependence of the gain coefficient on the laser intensity but also on the length of the excitation laser stripe. The results are presented as a function of the average intensity in W/cm2, which is a manner to express the threshold intensity for a direct comparison between different materials, independent of the setup used.

Blue surface-emitting distributed feedback lasers based on TPD-doped films

“…Note that, in the typical ASE setup, the size of the pump stripe is 3:5 mm. Dependencies of the ASE thresholds with the length of the pump stripe have also been observed by other authors, in that case with a poly(phenylene vinylene) derivative [44]. Because in our DFB setup a spot of only 1:3 mm in diameter is used, the thresholds determined are not the optimized ones.…”

“…Thus, we decided to express the thresholds measured in the DFB setup in energies per pulse and use a similar film without grating to assess the effect of the grating on decreasing the threshold. All the considerations just stated justify the lack of coherence in the threshold values found in the literature [2,8,31,34,38,[40][41][42][43][44][45][46][47]. Very often, the ASE thresholds reported for certain materials are apparently lower than the laser thresholds measured for the same materials inside a resonant cavity.…”

Modal gain enhancement by cylindrical waveguide and gain saturation in CdSe nanocrystal quantum dots

“…However, analysis of modal gain has been limited in the non-saturation regime due to ignorance of length-dependence of the modal gain. Recently, a few works have pointed out length-dependence of modal gain saturation [1,8,9]. Additionally, NQDs can be easily incorporated with various geometric cavities [10].…”

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

“…Silvestre et al reported a formalism to retrieve optical gains from VPI measurements, [25] but their method has not gained much traction, probably because their assumptions were not too realistic. [26,27] As we have seen, up to three analogous but independent experiments (SES, VSL, VPI) are currently required to fully characterize the ASE properties of active thin films (losses, gains, and threshold).…”