RF-photogun as ultra bright terahertz source

Recently research into new terahertz (0.3 to 30 THz) light sources has gained a lot of interest. Especially compact sources capable of delivering high peak fields (?? 1 MV/cm), in a short pulse. To achieve this,we will use short relativistic electron bunches, created by photoemission and accelerated in an rf-photogun, to create THz light by means of coherent transition radiation. Because wavelengths smaller and comparable to the bunch length add up coherently, the intensity scales with N2, with N the number of electrons in the bunch. In the first experiments we expect to create THz light pulses with a bandwidth of 1 THz and 1 µJ per pulse. If such a light pulse is focused on a spot of radius 250 µm, this corresponds to peak electrical fields of 1 MV/cm. The eventual goal is to increase the bandwidth of the source, by creating shorter electron bunches. This will be accomplished by choosing a suitable radial laser profile, leading to ellipsoidal electron bunches, which can be focused and compressed very effectively. Eventually this will lead to THz pulses with a bandwidth of 10 THz and energy of 100 µJ. This corresponds to peak electrical fields of 10 MV/cm and higher.