Study on Production of Coherent Light by SASE

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We have conducted research on SASE (Self-Amplified Spontaneous Emission), which is expected to be a promising candidate for realizing X-ray lasers, in the infrared region using the L-band linac, which can accelerate a single-bunch electron beam with charge up to 91 nC.The characteristics of the electron beam have been measured over the wide energy range of 11-32 MeV to be the relative energy spread 1.1〜4%, charge per bunch > 20 nC, the bunch length 20-30 ps, and the normalized emittance 150〜250 π mm mrad. The expected performance of SASE has been estimated using these measured parameters and SASE theory based on the 1-dimensional model. The FEL parameters is 0.022 and the gain length is 0.128 m for the electron energy 11 MeV and the K value of the wiggler 1.47. It has been found the theory is applicable for the peak current > 1kA and the electron energy < 20 MeV.We have measured strong light emitted when the electron beam of 12.6 MeV passes through the wiggler with 6 cm period length and 32 periods. The peak power of the observed light increases from 1 W to 1 kW as the K-value increases. Since the K-value dependence of the power agrees quite well with the prediction of the theory, it is concluded that the observed light is due to SASE.We have measured wavelength spectra of SASE over the range of 80-180 μm using a grating monochromator. The spectral width of the fundamental peak ranges 2-3 %, and this value is slightly larger than 2.2-2.3 %, predicted by the theory. We have observed the second harmonic peak of SASE for the first time. We are quantitatively measuring characteristics of SASE and analyzing experimental results using 3-dimentional FEL simulation codes.