Concepts for ultraviolet-free electron laser optics

Scientists at Brookhaven National Laboratory have developed a design for an ultra-violet free electron laser (FEL) facility utilizing a seeded-amplifier approach. Since the accelerator is a single-pass device, resonator and outcoupler mirrors (which are a difficult aspect of oscillator FEL designs) are not required. The result is a source of high peak power vacuum ultraviolet radiation with the mode structure, bandwidth and frequency stability of the input seed laser. The accelerator provides pulses of radiation at up to 10 kHz, so to maximize the utilization of the source, novel optical systems to share the radiation had to be developed. These include specialized alignment, beam transport, order sorting, and multiplexing optics. In addition, FEL-on-FEL pump-probe experiments are made possible by a variable optical delay of up to 10 ns operating in the wavelength range of 200 to 75 nm. Some aspects of the FEL design are also described to clarify the constraints and choices for the optical system.