Dinh C. Nguyen (LANL)
Self-amplified spontaneous emission (SASE) has been theoretically studied and experimentally demonstrated to be a powerful method of coherent generation of electromagnetic radiation. This high-gain single-pass free-electron laser (FEL) approach has recently received considerable interest as it shows potentials toward the generation of coherent x-rays without the need for resonator mirrors. Experimentally, large SASE gains have been demonstrated in the millimeter wave and infrared regions. Recent results in the visible and deep ultraviolet regions also reported substantial gains. Nevertheless, saturation in the single pass SASE FEL has not been achieved.
It has been recognized early on that the combination of a small seed signal and an adequately large single-pass gain can achieve saturation with a much shorter undulator compared to that of the single-pass SASE approach. Injection seeding a high-gain SASE undulator with an optical signal allows the SASE process to start from a finite radiation power rather than random noise, thereby improving the amplitude and wavelength stability of the output radiation.
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