In high-gain free-electron lasers (FELs) with planar undulators it is possible (in the linear regime) to independently amplify at the fundamental and at odd harmonics, a process referred to as Harmonic Lasing (HL). For the HL process preservation of the quality of the incoming high-brightness electron beam is essential. This requires suppression of the lasing at the fundamental, which can be achieved using several methods such as special phase shifter set points and attenuation of the fundamental radiation using intra-undulator optical high-pass filters. The European XFEL variable-gap undulator beamline SASE2 features two intra-undulator stations combining a magnetic chicane and the possibility to insert a thin diamond crystal onto the optical axis of the beamline. While installed for the operation in hard x-ray self seeding (HXRSS) mode, this hardware is well-suited for HL experiments at a low electron beam energy corresponding to a fundamental photon energy of about 2keV. In this contribution we present numerical simulations of third-harmonic lasing at this working point.

Version 4 of the widely used time-dependent FEL code Genesis 1.3 has been released. The C++ code keeps the entire bunch in memory and thus allows for self-consistent effects such as wakefields or long-range space charge fields. With sufficiently allocated distributed memory, Genesis 1.3 can represent each individual electron. This solves the problem of the shot noise statistics at any arbitrary frequency in the simplest way and allows for sorting and redistribution of particles among the computer cores for advanced FEL applications such as the Echo-Enabled Harmonic Generation schemes. This presentation reports on the new physics added to the code as well as features which simplify the setup of the simulations as well and the ability to link user-made libraries to adapt to the specific needs of each user.