The petawatt field synthesizer (PFS) is a high-power optical parametric chirped-pulseudamplification (OPCPA) system under development, which aims at generating fewcycleudpulses with high energies of several Joule. The availability of light pulses withudthese unique parameters will enable an efficient generation of even shorter attosecondudpulses with significantly higher photon flux than achievable today [1]. Notudonly the real-time observation, but also the control of charge transfer in molecularudsystems will become feasible for the first time [2].udThe technique for realizing the ambitious PFS specifications is short-pulse pumpedudOPCPA in mm-thin crystals. The reduced crystal thickness allows for ultra-broadbandudamplification. The pump-pulse duration is reduced to a picosecond—compared toud100 ps to nanosecond pump-pulse duration in conventional high power OPCPA systems.udThe shortened pulse duration facilitates higher pump intensities whereby anudefficient amplification in the mm-thin crystals is achieved.udThe demonstration of this novel scheme in the PFS project will allow its use inudthe extreme light infrastructure (ELI)[3]—a pan-European high-power laser project.udBased on the PFS technology for the front end, the ELI will generate exawatt peakpowerudpulses and therefore facilitate the study of laser-matter interaction in an unprecedentedudintensity range [4].udThis work describes the CPA-aspects of a suitable chirped pulse amplification (CPA)udpump laser for the PFS OPCPA system. The diode-pumped Yb:YAG amplifiers up toudan energy of 300 mJ (at 1030 nm) are presented in combination with the dispersionudmanagement. The application of spectral-amplitude shaping in conjunction withudan Yb:glass amplifier with broader bandwidth than Yb:YAG enables an unprecedentedudbandwidth of 3.5nm in the Yb:YAG amplifier at this energy level. Simulationsudshow that a similar bandwidth can be maintained for the full amplifier system.udThe pulses with 200 mJ could be compressed to 900 fs, close to the transform limit.udLater changes in the stretcher increase the bandwidth more and compression downudto 740 fs is demonstrated. To date, these are the highest peak power pulses generatedudin Yb:YAG. For the application as OPCPA pump, the so generated pulses areudfrequency doubled in a DKDP crystal.udAnother key aspect of this work is the synchronization of the OPCPA pump andudsignal pulses. In spite of optical synchronization of both pulses, a large timing fluctuationudbetween these pulses is measured at the first OPCPA stage. The high accuracyudjitter measurement setup and a series of measurements, which showed that theudstretcher/compressor setup is the main source of jitter, are presented. Theoreticaludinvestigations yield that the optical delay in a compressor is orders of magnitudeudmore sensitive to angle changes compared to free space propagation. This makes theudstretcher and compressor extremely sensitive for timing jitter caused by turbulentudair or mechanical instabilities. This novel insight helped us to significantly reduceudthe jitter to 100 fs and to demonstrate the feasibility of the PFS concept with firstudbroad-band OPCPA experiments.
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