Figure 5
Spatial profiles of the focused beam with the KB mirror in the (a) horizontal and (b) vertical direction, measured at λ = 12.4 nm with the knife-edge scan method. The red circles are measured results, while the dashed lines are Gaussian fits. The knife-edge scan measurement was performed in the vacuum chamber using a gold wire, motorized stages and a silicon photodiode. The soft X-ray FEL pulse energy was reduced using the gas attenuator at an N2 pressure of 70 Pa combined with 1.1 µm Zr foil to eliminate the contribution of the higher-order harmonics. |