AUTHOR=Nishijima Yoshiaki , Juodkazis Saulius TITLE=Optical Characterization and Lasing in Three-Dimensional Opal-Structures JOURNAL=Frontiers in Materials VOLUME=2 YEAR=2015 URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2015.00049 DOI=10.3389/fmats.2015.00049 ISSN=2296-8016 ABSTRACT=

The lasing properties of dye-permeated opal pyramidal structures are compared with the lasing properties of opal films. The opal-structures studied were made by sedimentation of microspheres and by sol–gel inversion of the direct-opals. Forced-sedimentation by centrifugation inside wet-etched pyramidal pits on silicon surfaces was used to improve the structural quality of the direct-opal structures. Single crystalline pyramids with the base length of ~100 μm were formed by centrifuged sedimentation. The lasing of dyes in the well-ordered crystalline and poly-crystalline structures showed a distinct multi-modal spectrum. Gain via a distributed feedback was responsible for the lasing since the photonic band gap was negligible in a low refractive index contrast medium; the indices of silica and ethylene glycol are 1.46 and 1.42, respectively. A disordered lasing spectrum was observed from opal films with structural defects and multi-domain regions. The three-dimensional structural quality of the structures was assessed by in situ optical diffraction and confocal fluorescence. A correlation between the lasing spectrum and the three-dimensional structural quality was established. Lasing threshold of a sulforhodamine dye in a silica opal was controlled via Förster mechanism by addition of a donor rhodamine 6G dye. The lasing spectrum had a well-ordered modal structure, which was spectrally stable at different excitation powers. The sharp lasing threshold characterized by a spontaneous emission coupling ratio, β ≃ 10−2, was obtained.