Gain Measurement on the ACO Storage Ring Laser

We report the results of the first gain measurements on the free electron laser being assembled on the storage ring ACO. The largest measured peak gain, averaged over the laser mode, is Ĝ = 4.3 × 10
^-4
per pass. No laser induced bunch lengthening is observed within the experimental accuracy of 50 psec under a laser intensity of 1.6 kw/cm2 and under the conditions of strong anomalous bunch lengthening (σ
_τ
/σ
_τ
(I=0)) = 6.8 - 4.2.