Terawatt-Peak-Power Single-Cycle Infrared Fields

We propose the development of a novel infrared source delivering ~10-mJ, sub-10-fs phase-stable terawatt-peak- power electromagnetic waveforms at a center wavelength of 1.5 m. The infrared source is based on multi-mJ all- optically synchronized and phase-stable optical parametric chirped-pulse amplification (OPCPA) at 1.5 m, subsequent spectral broadening in a gas filament, and final recompression to a pulse duration below two optical cycles using dispersive mirrors. The envisaged hybrid OPCPA-filamentation scheme avoids a number of severe problems of existing state-of-the-art technology and promises great advantages: (1) With the advent of a mature 200-fs Yb:KGW diode-pumped solid-state MOPA system it became possible to abandon the Ti:sapphire front-end which in current systems represents a bottleneck for upscaling the achievable pulse energy; (2) we avoid working close to the signal-idler wavelength degeneracy and reduce the quantum defect for the signal wave; (3) we employ (nearly) collinear Type II phase matching that, as opposed to Type I, supports a much narrower bandwidth but is free of parasitic self-diffraction; (4) Although OPCPA systems can deliver output spectra with >200 nm bandwidth, the quality of the resultant compressed pulses remains poor due to intrinsically steep slopes of parametrically amplified spectra. In contrast, external spectral broadening in gas filaments provides low-intensity broad spectral wings essential for few-cycle pulse formation. After completion of the source, we intend to use it in two selected high-field experiments: (a) investigation of 1.5-m-field-driven high-harmonic generation: Our novel 1.5-m source with high ponderomotive energy (Up ) will be perfectly suited for generating high-energy electrons and for extending the high-harmonic generation (HHG) cutoff into the kiloelectronvolt region. Of particularly interest for us are the influence of propagation effects on the HHG output and the concept of self-phase matching that, for 1.5-m driver pulses, was predicted to permit the generation of isolated ~60-attosecond pulses at ~230 eV photon energy from plateau harmonics. Such pulses would be the shortest light pulses ever created by mankind and they would open the door to a larger number of physical phenomena that could be studied by attosecond pump-probe type experiments. (b) attosecond surface photoelectron spectroscopy with suppressed ATI background: The development of infrared high-Up -sources is also of paramount importance for attosecond photoelectron spectroscopy of solid surfaces. Such experiments are significantly more difficult than in the gas phase for a number of reasons (e.g., the solid target cannot continuously be replaced, severe background problems due to above- threshold ionization (ATI) electrons, impossibility of ion-detection schemes). For attosecond surface photo-electron spectroscopy, infrared high-Up -sources are superior to Ti:sapphire sources because they exhibit stronger ponderomotive streaking effects for the same incident intensity.