1D and 3D photonic crystal structures towards field enhancement, sers and optical limiting studies

The ease of steering light with photonic crystals (PhCs) for the optical wavelengths, meeting the Bragg diffraction, has advanced the field of photonics with the development of low loss optical waveguides, electrically pumped ultra-low threshold lasers, optical switches and chemical and biochemical sensors etc. In this regard, we will be presenting here our recent results in 1D and 3D periodic dielectric structures, in particular the precise field confinement and enhanced field densities in these periodic dielectric structures. This enhancement of field densities was confirmed through studies on Raman scattering and nonlinear optical absorption. A metal dielectric of 3D colloidal crystal structure (MDCS) was employed in order to enhance the otherwise weak Raman signals by the combined effects of localized surface plasmon resonance (LSPR) enhancement due to gold nanoparticles, and electric field confinement for the dielectric and air band wavelengths corresponding to photonic band gap of the periodic dielectric structure. This intense electric field strength is employed to study the Raman scattering signals of adsorbed benzenethiol (BT) molecule on the MDCS. Large enhancement for the Raman signal in MDCS in comparison to the Raman spectra observed for BT molecule dispersed on sputtered gold film shows the effectiveness of MDCS for the micro level detection of the analyte. A large enhancement in nonlinear absorption (NLA) was observed in 1-D photonic crystal containing SiO2 and TiO2 thin films with a ZnO defect fabricated by RF sputtering technique. Scanning electron microscopy (SEM) analysis reveals the surface morphology of multi-layer structures and visible transmission spectra shows the photonic band gap present from 430 nm to 600 nm and the resonance peak present at 549 nm due to the ZnO defect layer. The strong confinement of the optical field around the defect layer resulted in the enhanced nonlinear absorption from the ZnO defect layer.