Some nanophotonic applications involve interacting with light while others involve the emission of light. Examples of nanophotonic applications that involve the emission of light include quantum dots, OLED, sensor applications, and next generation silicon based emitting devices. Quantum dots are luminescent materials that are currently being studied for light emitting processes. Quantum dots are typically made from inorganic materials including cadmium, indium, lead, phosphorus, selenium, and sulfur. The wavelength of light produced from these materials is dependent on the size of the particle that is emitting the light. It is possible to produce light of specific color by strictly controlling the size of the quantum dot. General quantum dot particle sizes range from 10 to 100 nanometers in diameter.
An area in the science of nanophotonics that has been attracting attention and increasing promise over the last fifteen years is the area of two-photon materials and processes. Two-photon nanophotonics is the process involving the simultaneous absorption of two low energy photons by a material to produce a higher energy state (excited state). In theory, the energy of the excited state in the target molecule is equal to the sum of the two photons. Applications for two-photon materials include fluorescent imaging, sensitization, and next generation nanolithography.
This absorption process is very weak and is classified as a 3rd order nonlinear optical process. The intensity of simultaneously absorbing two photons to form a high energy state is extremely weak and requires a laser of a certain threshold in intensity. There are many applications that take advantage of the requirements for two-photon processes to take place. When two low power laser sources, where neither of which have sufficient power to initiate a two-photon process, are trained on an object at a 45° angle, there is sufficient photon flux to initiate a two-photon process at the point where the two laser sources cross. The result is a targeted activation within an object. An application of this targeted two-photon process is the creation of 2D or 3D objects through the use of two-photon initiated polymerization reactions. Photo Dynamic Therapy (PDT) is a well established example of the application of two-photon processes. PDT involves using light to activate photoactive medicines that are introduced into the body. PDT is used to treat different medical conditions including certain types of cancer. Recent and continued improvements in the materials, resolution, and fabrication efficiency will soon make many materials manufactured from two-photon processes a widespread reality.
Nanotechnology is a fast growing field that will continue to have an impact on the daily life of us all. Improvements in efficiency and manufacturing technologies will allow nanophotonic based applications to be found in every home in the future. Lighting panels based on OLEDs, light activated medicines delivered directly to the needed location in the body, and flexible display screens that can be rolled or folded are just some of the near-term products coming. Nanophotonics allows for the possibility of processes running at the speed of light instead of being limited to the speed of electrons.