Near field terahertz imaging and spectroscopy

In this presentation, we present our THZ ANSOM and characterisation of the system of generation and detection of terahertz waves. Recent reports show a great potential of apertureless near-field scanning optical microscopy (ANSOM or ASNOM) applied to terahertz (THz) frequency domain, also called far infrared domain (0.1 to 10 THz). THz imaging brings an improved optical contrast that enables the identification of unique rotational and vibrational responses of various materials within this frequency range. But main drawback of THz imaging is weak resolution of images, limited by diffraction. We have also developed a spectroscopic system based on an interferometric technique. It is possible to record the linear autocorrelation of the terahertz electric field by scanning the optical path between the two arms of a Michelson interferometer. The terahertz spectrum is then obtained by numerical computation of the Fourier transform. For each point of the 2D near field image, one can reach a spectroscopic information. Morphologic and spectroscopic analysis can be simultaneously proceeded.