The Free Electron Laser Group is engaged in a broad investigation of the physics and engineering of critical components of an advanced, accelerator-based coherent light source known as the free electron laser (FEL). The goal of this group is to advance the theoretical and experimental understanding of photoemission, beam dynamics, and radiation processes.

FELs have unique characteristics that set them apart from other light sources, namely their high power output and broad wavelength tunability. FELs have a significant advantage over many other light sources because they can operate in regions of the electromagnetic spectrum where no other lasers exist and can achieve extreme power output levels. The recent demonstration of up to 10 kW CW output power at Jefferson Laboratory's FEL program has fueled optimism that mega-watt power levels are attainable. Applications include national defense, medicine, and nanotechnology.

Critical to any free electron laser is the electron beam (i.e., free electrons) which forms the lasing medium. These electrons travel through a spacially periodic magnetic field (the "wiggler") which causes them to radiate light. The electric field of the emitted light interacts with the beam to create bunches of electrons separated by a distance equal to the optical wavelength. The intensity of this radiation is proportional to the square of the electron beam current. Thus, the quality and brightness of this beam critically determines the performance of the FEL.

The electron beam is generated at a photoinjector, or electron gun. This component, like the accelerator used to impart the requisite energy to the beam, is kept in medium ultra-high vacuum. Within the gun, light from an incident drive laser impinges upon the cathode surface, liberating electrons within the cathode which are then accelerated by an electric field. Electrons leave the cathode because of the photoemission effect: electrons absorb incident photons and gain sufficient energy to cross the barrier to vacuum.

Photocathode research, design, fabrication, modeling, and testing is an important task of the FEL group. In fact, nearly every stage of an electron beam's "journey" from its inception at the cathode to its acceleration and undulation through the wiggler are studied and modeled by members of the FEL group at Maryland and its research collaborators. Collaborators include the Naval Research Laboratory (NRL) in Washington, D.C., Science Applications International Corporation (SAIC) in McLean, VA, the Naval Postgraduate School (NPS) in Monterey, CA, Jefferson Laboratory (JLab) in Newport News, VA, Argonne National Laboratory in Argonne, IL, Los Alamos National Laboratory (LANL) in Los Alamos, NM, Brookhaven National Laboratory (BNL), Brookhaven, NY, and Advanced Energy Systems, Inc. (AES) in Medford, NY.

Funding for the UMD efforts of this program is provided by the Joint Technology Office (JTO) and the Office of Naval Research (ONR).