text: An evanescent field is a residue optical field that "leaks" during total internal reflection. This "leaking" of light fades off at an exponential rate. The evanescent field has found a number of applications in nanometer resolution imaging (microscopy); optical micromanipulation (optical tweezers) are becoming ever more relevant in research.
  In optical tweezers, a continuous evanescent field can be created when light is propagating through an optical waveguide (multiple total internal reflection). The resulting evanescent field has a directional sense and will propel microparticles along its propagating path. This work was first pioneered by S. Kawata and T. Sugiura, in 1992, who showed that the field can be coupled to the particles in proximity on the order of 100 nanometers. This direct coupling of the field is treated as a type of photon tunnelling across the gap from prism to microparticles. The result is a directional optical propelling force.
  A recent updated version of the evanescent field optical tweezers makes use of extended optical landscape patterns to simultaneously guide a large number of particles into a preferred direction without using a waveguide. It is termed as Lensless Optical Trapping ("LOT"). The orderly movement of the particles is aided by the introduction of Ronchi Ruling that creates well-defined optical potential wells (replacing the waveguide). This means that particles are propelled by the evanescent field while being trapped by the linear bright fringes. At the moment, there are scientists working on focused evanescent fields as well.
  In recent studies, the evanescent field generated by mid-infrared laser has been used to sort particles by molecular vibrational resonance selectively. Mid-infrared light is commonly used to identify molecular structures of materials because the vibrational modes exist in the mid-infrared region. A study by Statsenko et al. described optical force enhancement by molecular vibrational resonance by exciting the stretching mode of Si-O-Si bond at 9.3 μm. It is shown that silica microspheres containing significant Si-O-Si bond move up to ten times faster than polystyrene microspheres due to molecular vibrational resonance. Moreover, this same group also investigated the possibility of optical force chromatography based on molecular vibrational resonance.
  Another approach that has been recently proposed makes use of surface plasmons, which is an enhanced evanescent wave localized at a metal/dielectric interface. The enhanced force field experienced by colloidal particles exposed to surface plasmons 
  at a flat metal/dielectric interface has been for the first time measured using a photonic force microscope, the total force magnitude being found 40 times stronger compared to a normal evanescent wave. By patterning the surface with gold microscopic islands it is possible to have selective and parallel trapping in these islands. The forces of the latter optical tweezers lie in the femtonewton range.
  The evanescent field can also be used to trap cold atoms and molecules near the surface of an optical waveguide or optical nanofiber.