The aim of the UK FEL project is to study the characteristics of a single-pass FEL over a wide operating range, using a four-section 5 m wiggler yielding a maximum K value of 2.7. The laser is driven by the 165 MeV Kelvin Laboratory linac. It has a design operating wavelength range of 2-20 µm, although higher harmonics are also under investigation. We report direct measurement of optical gain using a cw CO2 laser between 9 and 11 µm. Simultaneous spectra are obtained of both gain and spontaneous emission as a function of linac energy or wiggler field as the tuning parameter. The linewidth obtained is close to that expected for homogeneous broadening, and the gain is consistent with that predicted theoretically for the current available. Strong enhancement of both spontaneous emission and measured gain is obtained in the presence of a high-Q FEL cavity, as expected by simple considerations of optical confinement. These results imply that despite the shortness of our macropulse (~ 2.5 µm), it will be possible to diagnose buildup to oscillation from an injected signal. © 1987.
|Number of pages||7|
|Journal||Nuclear Inst. and Methods in Physics Research, A|
|Publication status||Published - 1 Sep 1987|