Proposed ultraviolet free-electron laser at Brookhaven Natl. Lab.: a source for time-resolved biochemical spectroscopy

Brookhaven National Laboratory is designing an ultraviolet free-electron laser (UV-FEL) user facility that will provide picosecond and subpicosecond pulses of coherent ultraviolet radiation for wavelengths from 300 to 75 nm. Pulse width will be variable from about 7 ps to ≈ 200 fs, with repetition rates as high as 10⁴ Hz, single pulse energies > 1 mJ and, hence, peak pulse power > 200 MW and average beam power > 10 W. The facility will be capable of `pump-probe' experiments utilizing the FEL radiation with: (1) synchronized auxiliary lasers, (2) a second, independently tunable FEL beam or, (3) broad- spectrum, high-repetition rate recirculating superconducting linear accelerator which feeds pulses of electrons to two magnetic wigglers. Within these two devices, photons from tunable `conventional' lasers would be frequency multiplied and amplified. By synchronously tuning the seed laser and modulating the energy of the electron beam, tuning of as much as 60% in wavelength is possible between alternating pulses supplied to different experimental stations, with Fourier transform limited resolution. Thus, up to four independent experiments may operate at one time, each with independent control of the wavelength and pulse duration.