Observation of optical diffraction radiation from a slit target at KEK accelerator test facility

We investigated diffraction radiation in optical wavelength range (ODR) as a possible tool for non-invasive transversal beam size measurements at KEK-ATF extraction line. We have designed and constructed an experimental setup consisting of the target chamber, rotatable mirror and two detectors: CCD camera with an image intensifier and a photomultiplier. The target was a silicon wafer covered with gold for better reflectivity. We have measured ODR angular distributions with and without polarization filter and dependencies on the target position with and without optical filters. We can say that the dependence on the beam size does exist. To be able to measure the beam size with a proper accuracy we need to reject the synchrotron radiation (SR) contribution reflecting from the target, which is an obstacle in our investigation. Results of our first observation of ODR from a slit target agree with theoretical model quite good. If all technical difficulties are solved, this non-invasive technique may be used for micron size beam measurements.