Another step towards shorter and brighter pulses: first successful observation of superradiance in FEL

At Brookhaven National Laboratory, United States, researchers have recently found a novel way to generate a very short controllable free electron laser (FEL) pulse, which usually depends on the length of the electron pulse. The main idea is the use of a Ti:Sapphire laser that combines a 150 femtosecond (FWHM) pulse of light with the much longer electron beam. This leads to a femtosecond FEL pulse that keeps growing in intensity and shortening in time duration, which is attributed to a phenomenon called superradiance (for details, see, R. H. Dicke, Phys. Rev. 93, 99 (1954)). The present research is the first to experimentally observe the effects of superradiance in a FEL setup. The output FEL pulse duration was measured to be as short as 81 femtoseconds, a roughly 50% reduction compared to the input seed laser. Understanding how to produce these intense, ultrafast pulses of light could help scientists around the world as they begin to construct the next generation of light source facilities. For more information, see the paper, "Experimental Characterization of Superradiance in a Single-Pass High-Gain Laser-Seeded Free-Electron Laser Amplifier ", T. Watanabe et al., Phys. Rev. Lett. 98, 034802 (2007).