Polymeric semiconductors spin-coated onto the photoresist grating form discontinuously distributed flocci,which do not fill grating grooves with nanoscale widths.Thus,the polymer layer neither forms a continuous gain channel nor creates a waveguide that enhances the distributed feedback(DFB)mechanism provided by the grating structures.This is verified by the microscopic and spectroscopic investigations on the topographic surface of the polymer-covered grating as it is etched layer by layer using oxygen plasma.This gives more insights into the mechanisms involved in optically pumped polymer lasers and provides new guidance for constructing DFB lasers.
