User:Steve Quinn/Plas lens

The Plasmonic Lens is intended to manipulate and focus stimulated surface plasmon polaritons (SPP), resulting in a focus beyond the limitations of conventional lenses. This limitation is known as the diffraction limit and the experimental plasmonic lens is intended to produce image details that are not possible with conventional lenses, below the diffraction limit. These image details are intended to be available at wavelengths smaller than the wavelength of visible light. Another name for this result is "subwavelength imaging". Hence, the physical resolution limit can be overcome with this method. SPPs have been extensively studied, and are produced when light interacts with evanescent waves in the near field interface of conjoined metal and dielectric materials. Its intended uses are focusing, imaging, light beam shaping, subwavelength optics, subwavelength light wave guiding, novel optical and magneto-optic data storage, light generation, microscopy, biophotonics, biological molecule sensors, and solar cells, as well as other applications.

Surface plasmon polaritons
Surface plasmon polaritons (SPPs) have been studied extensively, and became important to the surface sciences after the pioneering results produced by R.H. Ritchie, reported in 1957.

Overview
When focusing by means of surface plasmon polaritons (SPPs), some plasmonic lenses utilize extraordinary transmission. This is accomplished with nanoscale slits, periodically patterned within an ultra-thin metal film. The edge of each slit becomes points of multiple sources, where light can couple with the SPPs. The SPPs are excited by the incoming light. Various wavelengths of light couple with the SPPs with only a single sample.

The resolution of almost all conventional optical systems are governed by the diffraction limit. The evanescent components of an illuminated object can be focused in the near-field region, below the diffraction limit. This allows them to break the conventional barrier of the diffraction limit, and leads to the formation of concentrated light spots at nanometer (sub-wavelength) scales.

Utilizing negative index materials
The theoretical perfect lens, and the experimentally realized super lens and hyperlens, are types of plasmonic lenses.

The concept of a “perfect lens” was first proposed by John Pendry in 2000 which centered on applying a negative index material. When permittivity and magnetic permeability both have the correct values of -1, then the negative refractive index material becomes a perfect lens. Because of the dispersion and absorption in the materials, the conditions of permittivity equaling -1 and permeability equaling -1 is problematic for the natural materials.

Superlens
Hence, although the perfect lens may not exist, the superlens which can provide higher resolution beyond the diffraction limit has been proved. The superlens was analyzed in 2003 and proved by Xiang Zhang's research group in 2005 and researched by other groups as well.

Because the electric and magnetic responses (permittivity and permeability) of the materials were decoupled in the near field, only the permittivity needs to be considered for the desired electromagnetic radiation. This makes noble metals such as silver natural candidates for optical superlensing, and Zhang's group chose silver. Hence, by employing enhanced transmission, and appropriate interaction with surface plasmons, the superlensing effect was produced. Yet, the images imaged by the superlens are the same size as the objects. Hence, there is no working distance. Further work led to the hyperlens.

Nanoscale metallic structures
Two approaches to tuning methods for the purpose of phase modulation are presented. These are called "depth tuning" and "width tuning".

Depth-tuned structures have three types of plasmonic slits (convex, concave, and flat/constant groove depth) with different stepped grooves. Each have been designed and fabricated to achieve efficient plasmonic focusing and focal depth modulation of the transmitted beam. One application of depth-tuned plasmonic lens is focused ion beam milling.