Circular dielectric gratings acting as resonators for solid state polymer lasers

摘要

We report on an optically pumped polymer laser based on a circular grating resonator. The circular gratings were fabricated by electron beam lithography into a fused silica substrate. Due to the importance of a precise circularity of the grating we used a Leica LION LV1 electron beam writer allowing for smooth curved grating lines. A thin film of a methyl-substituted ladder-type poly(p-phenylene), spin-coated onto the gratings, acts as active material. Since the grating period satisfies the second-order Bragg condition it provides a true 2D feedback for the emitted photons of the polymer. At the same time surface emission is achieved via first order diffraction normal to the sample surface. Using short pulse laser systems for optical pumping we observe a clear lasing threshold, highly directed emission and a narrow spectral linewidth. By changing the grating period one can tune the emission wavelength over the entire gain region of the polymer.