Coherence imaging

Because interferometers are not limited by an input slit, they are naturally suited to high-throughput 2-d spectral imaging.  Generally the optical path length is scanned and an inverse Fourier transform applied to obtain the source spectrum. However, when spectral information content in a given scene is small (M unknowns), it suffices to image the optical coherence (interferogram) of the light emission at a small number (N>M) of optical delays in order to capture this information.  We have developed and patented a number of electro-optic and polarization-based optical systems employing temporal and/or spatial multiplex techniques to efficiently capture this 2-d information.

 

Plasma physics applications for coherence imaging include Doppler spectroscopy, polarization spectroscopy (motional Stark effect and Zeeman), spectral line ratio measurements and broadband imaging such as bremstrahhlung and blackbody.  The technologies span the spectrum from 200nm through to mid IR (5um).

 

Camera systems are either being developed or are presently deployed at the ANU, the University of Sydney, Consorzio RFX (Italy), Max Planck Institute for Plasma Physics, Greifswald (Germany) and Korean Basic Science Institute (KSTAR).

 

 

This animated gif shows 2-d images of the evolution of the HeII ion temperature during power-step ECH heated discharges in the WEGA stellarator. The ions are clearly heated by conduction from the edge-heated electrons.  The horizontal image direction is parallel to the toroidal magnetic field. The toroidal helical nature of the confinement region is evident from the shape of the isotherms in the edge regions. The weak grid pattern evident at early times is a residual imprint from the protective wire screen installed over the open port face.