Femtosecond lasers are an integral part in next generation light sources. In this presentation, we discuss some of the laser technologies and physics central to the development of X-ray FELs. First the origin of ultralow timing jitter of femtosecond lasers is explained and its consequences for the development of photonic systems operating with few attosecond precision and eventually even below is discussed. As an example, long term stable timing distribution for large scale x-ray FELs is shown. Currently, such systems operate with sub-10 fs precision over a week and first prototype systems are implemented at the FERMI FEL in Trieste. Timing distribution systems approaching attosecond level precision seem to be possible. Second, we discuss the production of laser radiation in the EUV and XUV via high harmonic generation, which eventually can be used for seeding of X-ray FELs. We have derived and experimentally verified closed form analytic expressions for high harmonic conversion efficiencies and discuss strategies and limitations for efficient EUV sources. Third, we discuss our progress in the development of an energy and power scalable sub-cycle waveform synthesizer for isolated attosecond pulse generation. The synthesizer is based on two few-cycle optical parametric chirped pulse amplifiers (OPCPAs) at 800 nm and 2 micron seeded from a single octave spanning carrier-envelope phase stabilized Ti:sapphire laser. This system delivers loosely synchronized and carrier-envelope phase stabilized 800 nm and 2 micron pulses for attosecond pulse generation. In a subsequent tight synchronization stage using balanced optical cross-correlation a high energy sub-cycle optical pulse is synthesized. Currently, this system is pumped by a Nd:YLF laser system. For pushing the output pulse energy of the sub-cycle pulses to the multi-mJ range at multi-kHz repetition rates a 100 W pump laser system based on cryogenically cooled Yb:YAG is under development. Progress towards reaching 50-mJ, 10-ps pulses at 2kHz repetition rate will be discussed.
