Coherent off-axis undulator radiation

There has been much interest in recent decades in obtaining coherent radiation from relativistic free electrons. This study explores the subject of coherent off-axis undulator radiation (COUR). Radiation is produced by passing relativistic short electron bunches through an undulator and observing the radiation at angles to the beam axis. It is shown in this study that for wavelengths longer than the electron bunch length, coherent radiation is produced. Since this radiation depends on the bunch length, the possibility exists to use COUR as a bunch length diagnostic.; The purposes of this study are: (1) to develop the theory of off-axis undulator radiation, (2) to observe COUR, and (3) to evaluate the effectiveness of using coherent radiation such as COUR as a bunch length diagnostic.; In describing off-axis undulator radiation, two methods of electromagnetic analysis are used: a multi-mode approach, where the radiation is described as an expansion of Gauss-Laguerre optical modes, and a Liénard-Wiechert approach, where the radiation is described as a field derived from Liénard-Wiechert potentials. The methods agree with each other, and the results of detailed calculations describing off-axis undulator radiation are presented.; An experiment to observe COUR was performed at Brookhaven National Laboratory on a 230 MeV linear electron accelerator, using a 12-period undulator. The radiation was detected with a low-temperature bolometer detector operating at 4.2 K. Experimental results showed that coherent bunch-length-dependent radiation was observed. While undulator radiation was present, most of the radiation observed originated from an upstream accelerator component. Future studies may isolate the undulator radiation.; The coherent bunch-length-dependent radiation that was produced is extremely sensitive to changes in the bunch length. It therefore acts as an effective bunch length diagnostic.