What is the difference between near-field optical microscopy and far-field microscopy?
What is near-field optical microscope?
Since the 1980s, with the advancement of science and technology towards small-scale and low dimensional spaces and the development of scanning probe microscopy technology, a new interdisciplinary field has emerged in the field of optics - near-field optics. Near field optics has revolutionized the traditional optical resolution limit. The emergence of the new type of Near Field Scanning Optical Microscope (NSOM) has expanded people's field of view from half the wavelength of incident light to a few tens of wavelengths, namely the nanoscale. In near-field optical microscopes, the lens in traditional optical instruments is replaced by a small optical probe with a tip aperture much smaller than the wavelength of light.
In 2008, Synge proposed that by shining incident light through a small hole with an aperture of 10nm onto a sample at a distance of 10nm, scanning and collecting micro area optical signals at a step size of 10nm, ultra-high resolution could be achieved. In this intuitive description, Synge has clearly predicted the main features of modern near-field optical microscopes.
The optical resolution based on near-field optics technology can reach the nanometer level, breaking through the resolution diffraction limit of traditional optics. This will provide powerful operational, measurement methods, and instrument systems for many fields of scientific research, especially the development of nanotechnology. At present, near-field scanning optical microscopes and near-field spectrometers based on hidden field detection have been applied in fields such as physics, biology, chemistry, and materials science, and their application scope is constantly expanding; Other applications based on near-field optics, such as nanophotography and ultra-high density near-field optical storage, nanophotonic components, capture and manipulation of nanoscale particles, have also attracted the attention of many scientists.
Apart from being called microscopes, there aren't many similarities.
Firstly, and also the biggest difference, the resolution is different. Far field microscopes, also known as traditional optical microscopes, are limited by diffraction limits and find it difficult to image clearly in areas smaller than the wavelength of light; And near-field microscopy can achieve clear imaging.
Secondly, the principle is different. Far field microscopy utilizes the reflection and refraction of light, and can be achieved by combining lenses; In the near-field, probes are needed to achieve the acquisition of optical signals through the coupling and conversion of the vanishing field and the transmission field.
Also, the complexity and cost of the instruments are not comparable.
