Gain optimization, bleaching, and e-beam structuring of IR-140 doped PMMA and integration with plasmonic waveguides

Abstract

The optimal IR-140 weight ratio concentration producing maximum gain in amplified spontaneous emission measurements in the near-infrared (~880 nm) is determined. The structures investigated consist of PMMA polymer thin films, doped with IR-140 dye molecules in 4 different concentrations (0.7%, 0.8%, 0.9% and 1.0%), spin-coated on a silica layer grown on silicon wafers. The maximum material gain was obtained for the 0.9% weight ratio sample. The polarization dependence of the gain medium was also investigated, and the gain found to be similar in the TE and TM orientations. Bleaching of the gain medium, characterized by a decrease in the material gain due to pumping, was also explored and found to be rapid for thin films. However, bleaching is reduced as the pump energy density is reduced, creating a trade-off between gain and film longevity. The bleaching disappears at a low pump repetition rate. The gain films were structured via e-beam lithography to demonstrate the feasibility of this method for integration of structured doped polymers within optical devices. Amplification of the long-range surface plasmon guided by a gold stripe covered by the gain medium is also demonstrated and the modal gain measured was measured (~65 cm −1) from which the material gain was deduced (~300 cm −1). The material should prove useful for demonstrating device ideas and concepts in plasmonics and nano-photonics.

Material gain concentration quenching in organic dye-doped polymer thin films

“…Early works investigated the influence of dye concentration, excitation intensity, and pulse width on lasing properties of liquid dye lasers [23,24]. However, for thin film polymer solid-state lasers concentration dependent lasing properties have not been widely reported despite the strong influence of the doping level and the host matrix [25][26][27]. In particular, the evaluation of the material gain is a prerequisite for the development and proper choice of dye molecules as well as the selection of suitable host polymers, as concentration quenching ultimately limits attainable modal gain.…”