Although irregular open nanostructures are typically inadequate for achieving strong light-matter interactions, incorporating irregularity can be advantageous as an alternative strategy, which is not affected by unavoidable structural variations and imperfections. In our recent study,1 we have demonstrated a framework to capitalize on natural disordered nanostructures as highly efficient optical resonators for light confinement and amplification. As one of the wondrous nanocomposite found in nature, the colors of mother-of-pearl (as also known as nacre) have been studied conventionally in terms of diffraction and interference. Surprisingly, we reveal that their color origin is highly attributed to the irregular and disordered nanostructures of nacre, in which disorder-driven resonances can be self-formed by multiple scattering without relying on well-configured closed cavities. We further demonstrate that the highly multilayered nanostructures of nacre can serve as a new class of disordered resonators to realize low lasing threshold and high energy conversion efficiency. Multiple resonances in such nanostructures, which are formed closely in frequency and space, can easily be overlapped to form hybridized states. This ensemble acting of multiple resonances drastically increases the effective cavity size, boosting light-matter interactions. For example, lasing action can be achieved using an edible food dye with a low quantum yield. Indeed, while ordered and closed resonators are commonly thought to be crucial, this biogenic approach can offer a novel strategy for designing and fabricating photonic nanostructures. The simplicity and efficiency of the natural resonators will open the new possibility of studying light propagation in complex media, measuring photoluminescence properties, and developing cost-effective photonic devices.
Compound eyes in arthropods demonstrate distinct imaging characteristics from human eyes, with wide angle field of view, low aberrations, high acuity to motion and infinite depth of field. Artificial imaging systems with similar geometries and properties are of great interest for many applications. However, the challenges in building such systems with hemispherical, compound apposition layouts cannot be met through established planar sensor technologies and conventional optics. We present our recent progress in combining optics, materials, mechanics and integration schemes to build fully functional artificial compound eye cameras. Nearly full hemispherical shapes (about 160 degrees) with densely packed artificial ommatidia were realized. The number of ommatidia (180) is comparable to those of the eyes of fire ants and bark beetles. The devices combine elastomeric compound optical elements with deformable arrays of thin silicon photodetectors, which were fabricated in the planar geometries and then integrated and elastically transformed to hemispherical shapes. Imaging results and quantitative ray-tracing-based simulations illustrate key features of operation. These general strategies seem to be applicable to other compound eye devices, such as those inspired by moths and lacewings (refracting superposition eyes), lobster and shrimp (reflecting superposition eyes), and houseflies (neural superposition eyes).
Surface-enhanced Raman scattering (SERS) spectroscopy can be a useful tool in regard to disease diagnosis and prevention. Advantage of SERS over conventional Raman spectroscopy is its significantly increased signal (up to factor of 106-108) which allows detection of trace amounts of substances in the sample. So far, this technique is successfully used for analysis of food, pieces of art and various biochemical/biomedical samples. In this work, we survey the possibility of applying SERS spectroscopy for detection of trace components in urinary deposits. Early discovery together with the identification of the exact chemical composition of urinary sediments could be crucial for taking appropriate preventive measures that inhibit kidney stone formation or growth processes. In this initial study, SERS spectra (excitation wavelength - 1064 nm) of main components of urinary deposits (calcium oxalate, uric acid, cystine, etc.) were recorded by using silver (Ag) colloid. Spectra of 10-3-10-5 M solutions were obtained. While no/small Raman signal was detected without the Ag colloid, characteristic peaks of the substances could be clearly separated in the SERS spectra. This suggests that even small amounts of the components could be detected and taken into account while determining the type of kidney stone forming in the urinary system. We found for the first time that trace amounts of components constituting urinary deposits could be detected by SERS spectroscopy. In the future study, the analysis of centrifuged urine samples will be carried out.
Proc. SPIE 8958, Understanding the nanophotonic light-trapping structure of diatom frustule for enhanced solar energy conversion: a theoretical and experimental study, 89580I (3 March 2014); doi: 10.1117/12.2038529
Recent designs in nanophotonic light-trapping technologies offer promising potential to develop high-efficiency thin-film solar cell at dramatically reduced cost. However, the lack of a cost effective scalable nanomanufacturing technique remains the main road-block. In nature, diatoms exhibit high solar energy harvesting efficiency due to their frustules (i.e., hard porous cell wall made of silica) possessing remarkable hierarchical nano-features optimized for the photosynthetic process through millions of years evolution. To explore this unique light trapping effect, different species of diatoms (Coscinodiscus sp. and Coscinodiscus wailesii) are cultured and characterized by Scanning electron microscope (SEM). Rigorous Coupled Wave Analysis (RCWA) and Finite-difference time-domain (FDTD) method are employed to numerically study the nanophotonic light-trapping effect. The absorption efficiency is significantly enhanced over the spectrum region centered on 450nm and 700nm where the electric fields are found strongly confined within the active layer. The transmission and reflection spectra are also measured by optical spectroscopy and the experimental results are in good agreement with numerical simulations.