The refractive index is the property of a material that changes the speed of light and describes how light propagates through the material. The refractive index is an important property of solar cells - the higher it is, the more incident light gets reflected and is not converted to a photocurrent. Solar cell manufacturers have developed various kinds of antireflection coatings to reduce the unwanted reflective losses. The purpose of these optical thin-films is to minimize the differences in the refractive indices between the ambient medium and the solar cells. For both solar cells and LEDs, coating with nanoparticles can enhance the performance without harming the electrical properties of the devices, as can occur with etching or lithographic processing. In new work, researchers have now have not only demonstrated this advantageous feature but also provided a strategy for optimizing the types and sizes of nanoparticles for use in both solar cells and LEDs.
By exploiting the outstanding properties of self-organizing materials, a team of Italian scientists has investigated a new way to build a bridge between two branches of physics: 'hard matter' and 'soft matter'. This allows researchers to address specific issues towards the realization of active-plasmonics devices, where the plasmonic resonance of gold nanoparticles can be finely controlled by means of external perturbations (electrical field, optical field, temperature). In place of a static approach - e.g. varying particles size, materials, etc. - the researchers used liquid crystals as active surrounding medium. This approach represents a 'scientific wedding' between the fascinating worlds of soft matter and plasmonics worlds.
Quick Response Codes, or QR codes for short, are two-dimensional matrix codes that can hold 100 times more data than a traditional barcode. QR codes have rapidly gained popularity and are now very commonly used in various products, because of fast readability and large storage capacity. Applying the concept of QR codes to security printing applications - think banknotes - researchers have now developed an invisible QR code made from nanoparticles. They applied upconverting inks to print QR codes on paper and transparent tape, using an aerosol jet direct writing machine. They produced QR codes with embedded security characters using blue and green upconverting inks. These codes are invisible to the naked eye but produce single- and multi-color upconversion luminescence images under near-infrared excitation which can be read and decoded with an unmodified smart phone.
Reducing the size of photonic and electronic elements is critical for ultra-fast data processing and ultra-dense information storage. The miniaturization of a key, workhorse optical instrument - the laser - is no exception. Coherent light sources at the nanometer scale are important not only for exploring phenomena in small dimensions but also for realizing optical devices with sizes that can beat the diffraction limit of light. Researchers at Northwestern University have now found a way to manufacture single laser devices that are the size of a virus particle and that operate at room temperature. They show that subdiffraction nanoresonators based on metallic bowties, when coupled to a gain material, can generate coherent and directional light emission.
The unique energy band structure in graphene allows it to actively respond to photons with ultra-wide spectrum range - from the visible to the infrared - with record strong inter-band transition efficiency. As a consequence, graphene based ultra-fast photonics has been rising fast in various aspects of ultra-fast photonics - an ultra-fast graphene photo-detector with bandwidth exceeding 500 GHz; a broadband graphene optical modulator; a broadband graphene polarizer etc, which all benefit from the material's broadband photonics property. Researchers have now experimentally demonstrated for the first time that graphene, besides its well-known optical saturable absorption, also shows microwave and terahertz saturable absorption. The results lead to the expectation that graphene may show potential applications in microwave photonics.
The size of pixels is one of the key limiting features in the state of the art of holographic displays systems. Holography is a technique that enables a light field to be recorded and later reconstructed when the original light field is no longer present, due to the absence of the original objects. The resolution and field of view in these holographic systems are dictated by the size of the pixel, i.e. the smallest light scattering element. To address the limitations of current holographic systems due to their pixel size, a research team set out to use nanostructures as the smallest possible light-scattering elements for producing holograms. They harnessed the extraordinary conductive and light scattering abilities of nanotubes and patterned an array of carbon nanotubes to produce a high resolution hologram.
Smart phones, tablets and other electronic gadgets have become an integral part of our daily life. To maintain the steady development to even faster and smaller devices, it is desirable to replace their slow electrical data interconnects with fast optical connections. Photonic crystals are an ideal tool for such a purpose as they can guide and bend light on a nanometer scale. Surprisingly, researchers have so far been unable to truly probe inside these crystals how the light intensity is distributed - this, however, is a requirement for being able to accurately characterize the local density of electromagnetic states inside the crystal which is the key for controlling the interaction of light with matter. Researchers have now demonstrated a new concept to measure the intensity distribution of light inside photonic crystals. This method, for the first time, allows researchers to map the absolute strength of an electromagnetic field component inside a photonic crystal.
The emission of light by a single molecule is a cornerstone of nano-optics that will enable applications in quantum information processing or single-molecule spectroscopy. However, a key challenge in nano-optics is to bring light to and collect light from nano-scale systems. In conventional electronics, the interconnect between locally stored and radiated signals, for example radio broadcasts or mobile phone transmissions, is formed by antennas. For an antenna to work at the wavelength of light it is necessary to downscale the structure by the same factor as the wavelength or the frequency of the wave, i.e. roughly by a factor of 10 million. Once the nanofabrication issues are sorted out, nano-optical antennas could become ubiquitous in all applications based on light-matter interactions such as sensing, light emission (e.g. LEDs) and detection, as well as light harvesting, i.e. for solar cell applications.