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Science with Light at Jefferson Lab

FEL Spectral Range

Power as a function of wavelength for various sources, the lasers all being sub-picosecond

The superconducting technology that Jefferson Lab pioneered for nuclear physics research with electron beams now also serves science conducted at JLab with light: biology, medicine, chemistry, environmental science, materials science, condensed-matter physics, nanotechnology. Because JLab's initial, principle-proving light-source capabilities exceeded those of established conventional sources, initial experiments yielded some 100 papers in leading journals. Then, in 2003, substantially upgraded light-source capabilities became available at the JLab Free-Electron Laser User Facility, offering research opportunities without parallel anywhere.

The upgraded JLab free-electron laser (FEL) is on-line as a wavelength-tunable, subpicosecond, >10 kW infrared light source offering a combination of high repetition rate and high power per pulse. The JLab FEL operates in regimes unattainable by subpicosecond tabletop lasers, even at a specific wavelength. It builds on the successes of JLab's principle-proving, kilowatt-scale "Infrared Demo" FEL. The IR Demo operated for scientific users from 1999 to late 2001.

An aggressive program is in place to shorten the FEL's light pulses down to the attosecond regime to meet frontiers of time as well as high field in a fully wavelength-tunable device. The upgraded FEL soon will also incorporate a kilowatt-scale ultraviolet capability.

"Driving" the FEL is a superconducting ERL. This energy-recovering linac—linear accelerator—is a small, higher-current cousin of JLab's huge CEBAF electron accelerator for nuclear physics. In the IR Demo, the ERL itself—using an electron-beam bending magnet—demonstrated production of broadband light over four orders of magnitude brighter than achieved anywhere before in the terahertz frequencies lying between electronics and photonics. The upgraded FEL's ERL is configured for further advances in this underexploited region of the electromagnetic spectrum.

JLab's ERL-driven FEL is the first of a new generation of accelerator-based light sources in which each electron circulates only once rather than being stored, as it would be in a typical synchrotron light source. Each electron's energy is recovered and almost immediately imparted to another electron in the ERL.

JLab IR Demo FEL results have begun changing thinking about linear and nonlinear dynamical processes. JLab's earlier kilowatt-scale FEL delivered light with subpicosecond time structure at enormously high repetition rates. A comprehensive bibliography of resulting publications appears on the FEL pages at . The papers derive from only 1872 hours of funding-limited operation for some 30 user collaborations at JLab's then-nascent light-source facility—an output well matched to those of established light sources. Moreover, in basic accelerator, beam, and photon physics, the FEL and ERL are opening regions of promising study for future research tools.

JLab FEL Specifications

Wavelength range (IR)1-14μm
Energy/pulse 120 μJ
Pulse repetition frequency Up to 75 MHz
Pulse length500-1700 fs FWHM
Maximum average power>10 kW
Wavelength range (UV/VIS)250-1000 nm
Energy/pulse 20 μJ
Pulse repetition frequency Up to 75 MHz
Pulse length300-1700 fs FWHM
Maximum average power>1 kW