Abstract
Saturation of a high-gain harmonic-generation free-electron laser (HGHG-FEL) at 266 nm has been accomplished at the Brookhaven National Laboratory/Deep Ultra Violet Free Electron Laser Facility (BNL/DUV-FEL) by seeding with an 800 nm Ti:sapphire laser. We describe the diagnostics used to characterize the electron beam and the FEL output. Analytic and simulation calculations of the HGHG output are presented and compared with the experimental data. We also discuss the chirped pulse amplification of a frequency chirped seed by an energy chirped electron beam. The third harmonic at 88 nm accompanying the 266 nm fundamental has been used in an ion pair imaging experiment in chemistry, the first application of the BNL/DUV-FEL.
Highlights
There is considerable interest in producing coherent radiation using single-pass FELs from deep UV down to the x-ray regime [1]
The radiation starts from shot noise; the pulse-to-pulse energy fluctuation is large and the light is not temporally coherent
In the HGHG-FEL [3,8,9], the electron beam is seeded by a conventional laser, which results in a stable central wavelength, excellent temporal and spatial coherence, and high pulse energy stability of the output radiation
Summary
There is considerable interest in producing coherent radiation using single-pass FELs from deep UV down to the x-ray regime [1]. The operation of a single-pass FEL in the self-amplified spontaneous emission (SASE) mode has been the subject of many recent studies [4 –7]. In this case, the radiation starts from shot noise; the pulse-to-pulse energy fluctuation is large and the light is not temporally coherent. In the HGHG-FEL [3,8,9], the electron beam is seeded by a conventional laser, which results in a stable central wavelength, excellent temporal and spatial coherence, and high pulse energy stability of the output radiation. Stability of the output pulse energy is limited by fluctuations in the accelerator, not the intrinsic shot noise of the electron beam. The output pulse length can be controlled by the seed laser, enabling the production of femtosecond pulses short compared with the electron bunch length
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