Article published Near field optics
Two microscopes in one!
In microscopy, a laser can be a source of illumination. It can also act as a high sensitivity amplifier for revealing the optical properties of materials.
A double microscope: this is how Serge Bouffard, the director of CIMAP*, describes the detection system which was developed and patented in collaboration with the Ecole Nationale Supérieure d'Ingénieurs at Caen. As with all near field microscopes, the topology of a material and of its optical properties can be characterised at the same time. However in this case the sensitivity is 10,000 times greater. The microscope also provides information on the phase of the analysed signal wave. How does it work? A laser illuminates the object whose surface is to be viewed, using a fibre optic drawn to a diameter of less than 100 nanometres. Detection of the vibration of the fibre gives topological information and the evanescent light, the wave propagated on the surface of the material, captured by the point provides information on its optical properties. The concept of this new system is that the evanescent light is re-injected into the laser via the optical fibre (this is termed optical retro-injection). The light is amplified by the laser with an enormous gain, but its phase is conserved. The variation associated with the laser emission makes it possible to determine the characteristics of the evanescent wave. Key advantage: unprecedented measurements of the characteristics of optical components, such as wave guides or thin films, for telecomms uses, among others.
* Centre de recherche sur les ions, les matériaux et la photonique - Centre for research on ions, materials and photonics (CEA-CNRS-Ensicaen laboratory).
