Enhanced lasing behavior enabled by guided-mode resonance structure embedded with double waveguide layers

Abstract

By doping a laser dye into two polyurethane layers in a guided-mode resonance (GMR) structure, we observed that the lasing emission can be enhanced by approximately fivefold. The structure comprises, from top to bottom, a grating layer, four alternating layers of polyurethane and ${\rm{T}}{{\rm{a}}_2}{{\rm{O}}_5}$, and a bottom substrate. Two different GMR wavelengths can be generated because of the two films of ${\rm{T}}{{\rm{a}}_2}{{\rm{O}}_5}$ serving as waveguide layers. The enhancement of the lasing emission is achieved by matching both the absorption and emission wavelength of the laser dye with the two GMR wavelengths. When the absorption wavelength matches the GMR wavelength, the formation of high intensity near the polyurethane layer serves to efficiently excite the laser dye. Additionally, as the emission wavelength overlaps with the GMR wavelength, the extraction of lasing intensity can be further increased in the preferred directions owing to the high reflection efficiency and directivity of the GMR. Moreover, we found that the linewidth is reduced to approximately 1.06 nm, and the estimated threshold is approximately ${0.92}\;{\rm{mJ}}/{{\rm{cm}}^2}$ when both excitation and extraction resonances occur in the waveguide structure.