Optical transition radiation measurements of the Los Alamos free electron laser driver

The authors have used the optical transition radiation (OTR) generated by the LANL FEL (Los Alamos National Laboratory free-electron laser) electron beam transiting a single mirrored quartz foil, and a two-foil OTR interferometer, to measure the electron beam´s divergence and spot size. Two gated intensified CID cameras are employed to monitor the OTR´s angular and spatial distributions simultaneously. This method allows a determination of the x and y emittances of the beam, when the beam is focused to an x or y waist, at a single position in the beam line. Both time-integrated and time-resolved measurements are possible with such a system. Time-integrated results are compared with those obtained by measuring the beam spot size as a function of magnetic quadrupole focusing strength, which inherently requires multiple beam pulses