FEL oscillation in IR region using a two-mode compact linac

Free-electron-laser of (FEL) oscillation at 14 μm using a two-mode compact linac is reported. FEL oscillation with a net gain of 7% is obtained using an electron beam with an energy of 24.8 MeV, peak current of 30 A, and pulse duration of 10 μs. Since an electron beam with good properties such as a low emittance and narrow energy spread is essential for the FEL oscillation, a low-emittance gun supplied with a high voltage of DC −200 kV and a klystron modulator having a precise voltage stability were developed. The linac can not only be operated as a FEL source but also an injector for a synchrotron radiation ring. This is the first such linac reported and is expected to enable cost-effective industrial use of FEL.