A SASE free electron laser optimization based on new generation in-vacuum undulators

► A fourth generation light source, i.e. self-amplified spontaneous emission (SASE) free electron laser (FEL), is optimized. ► New generation in-vacuum hybrid and superconducting undulators are discussed and compared. ► It is shown that the FEL wavelength should be down to soft X-rays (∼3nm) part of the spectrum via 1 GeV beam energy. ► Numerical calculations and simulation results are fairly well consistent.