Evanescent waves cannot be detected by standard microscopy methods as their energy remains bound to the surface and cannot reach out towards the microscope detector. This is a basic physical principle that limits the resolution of a microscope to about half the wavelength of a light.
Near-field scanning optical microscopy was developed to detect these waves and has subsequently become a significant tool in the study of materials, light-material interactions and biological samples. Near-field microscopy methods have evolved over the years and today they also incorporate advanced methods based on free electron fired on the surface.
Yet, near-field microscopy, as well as electron microscopy that provides similar information, suffer some drawbacks, the most notable of which is the limitation on real-time image display, a necessary ability to characterize nanoscale phenomena in real time.
In an article published in Nature Photonics, the faculty researchers present a new research approach to near-field microscopy that allows, among other things, to tackle this challenge with the help of the phenomenon of nonlinear wave-mixing – a prolific field of research that originated following the laser invention in the 60th. By launching a wide beam of light into the surface, Technion researchers were able to fully reconstruct the electromagnetic field of those evanescent waves and even demonstrated the application of this technology in monitoring changes in this field.
Nonlinear optical processes occur in high light intensities, where interactions between electromagnetic waves produce new waves with a different frequency. Such interactions can take place at any interface between two materials, making it an ideal platform for nanophotonics – which often deals with light at interfaces. Below some spatial limit, Information remains bound to the surface and cannot be seen by any camera. The new technique “releases” this information into radiation that can be detected by standard equipment.
The new scheme, named Nonlinear Near-field Optical Microscopy (NNOM), does not require anything other than a powerful commercial laser source and standard optical components and detectors. This, the researchers say, makes it not only affordable – but also approachable.
Read more – Nature Photonics>>>