Optical Characterization and Lasing in Three-Dimensional Opal-Structures

Yoshiaki Nishijima,Saulius Juodkazis

doi:10.3389/fmats.2015.00049

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 micro-spheres 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 Forster 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.

Highlights

Photonic crystals (PhCs) (John, 1987; Yablonovitch, 1987) fabricated by top-down or bottom-up methods are being used for a growing number of applications, such as spontaneous emission control (Li et al, 2007), micro lasing (Matsubara et al, 2008; Nishijima et al, 2008), and refractive index sensing (Nishijima et al, 2007; Kita et al, 2008; Wu et al, 2008)
One of the problems associated with the fabrication of large opal structures is the difficulty to control the crystalline quality of the face-centered-cubic opals even when the microspheres used for sedimentation have a small, ~1%, size distribution
When the same sedimentation conditions were used on cover glass substrates, poly-crystalline opal films with a thickness of up to 100 μm were formed with the typical single crystalline domains having a cross-section of 10–30 μm

Summary

Introduction

Photonic crystals (PhCs) (John, 1987; Yablonovitch, 1987) fabricated by top-down or bottom-up methods are being used for a growing number of applications, such as spontaneous emission control (Li et al, 2007), micro lasing (Matsubara et al, 2008; Nishijima et al, 2008), and refractive index sensing (Nishijima et al, 2007; Kita et al, 2008; Wu et al, 2008). The principles of photo-excitation and interaction of materials at atomic and molecular level in artificially engineered three-dimensional (3D) structures, such as photonic crystals (PhCs) (John, 1987; Yablonovitch, 1987), high-Q, and random and distributed feed back (DFB) cavities (Wright et al, 2004), are currently under active investigation due to prospects of miniaturization of opto-electronic devices, solar batteries, and creation of alternative light sources. The 3D confinement of photo-excited materials and control of their (de-)excitation by external cavity or via spatial localization of light–matter interaction has prospects to advance photonics into new multi-disciplinary fields Better understanding of these processes might lead toward miniaturization of opto-electronic devices. We demonstrate the formation of well-ordered opals by sedimentation in wet-etched micro-pits in silicon by fast centrifugation (Nishijima, 2009), which the single crystalline fcc opal photonic crystals with large area and short time can be obtained. The lasing properties of these dyes inside opal photonic structures show potential application in fluidic micro-laser field

Experimental

Results and Discussion

Conclusion