Final Report Summary - CYFI (Cycle-Sculpted Strong Field Optics)
The past decade saw a remarkable progress in the development of attosecond technologies based on the use of intense few-cycle optical pulses. The control over the underlying single-cycle phenomena, such as the higher-order harmonic generation by an ionized and subsequently re-scattered electronic wave packet, has become routine once the carrier envelope phase (CEP) of an amplified laser pulse was stabilized, opening the way to maintain the shot-to-shot reproducible pulse electric field.
Project CyFi takes advantage of several laser technologies and phase-control concepts with the aim to advance strong-field optical tools to a conceptually new level: from adjusting the intensity and timing of a principal half-cycle to achieving a full-fledged multicolor Fourier synthesis of the optical cycle dynamics by controlling a multi-dimensional space of carrier frequencies, relative, and absolute phases. Traditional “single-color” driver fields are frustratingly limited in their capacity to optimize the outcome of strong-field interactions that involve electron re-scattering on parent ionic cores because there is no flexibility in controlling electron trajectories. The practical advantage of replacing such sinusoidal driver fields with multicolour cycle-shaped waveforms is to enable electron trajectory engineering through which the yield and spectral brightness of secondary coherent emission—such as soft X-ray and Terahertz—can be increased by orders of magnitude.
During the project, the TU Vienna team, drawing on its extensive expertise in the CEP control and methods of laser and parametric amplification of ultrashort pulses, has developed and tested a version of an optical cycle shaper for strong field applications based on a commensurate-frequency multicolor pulse synthesis. The three-color driver pulses were successfully used to drive ionization and recombination processed in gas targets to observe prominent enhancements in the spectra of above-threshold ionization electrons and in the spectra of soft X-rays emitted by high-order harmonic generation. Compared to a single-color driver scheme under identical conditions and pulse intensity, the researchers have achieved at least a six-fold increase of the spectral brightness and at least a ten-fold increase of temporal intensity of attosecond X-ray bursts. The team has achieved few-cycle multicolor driver pulses of unprecedented energies reaching 25 mJ and has demonstrated multicolor-driven HHG spectra covering the whole water window in the soft X-ray spectral region.
Using an incommensurate-frequency pulse synthesis, the CyFi project team has also succeeded in experimentally verifying its assumptions about the feasibility to generate frequency-tunable THz pulses by controlling the electron micro-currents in a laser-induced gas plasma. A self-consistent theory explaining the mechanism of such emission was developed.
Driver pulses consisting of intense optical waveforms with sculpted optical cycles were also successfully applied to demonstrate the ability to pre-determine the ionization and dissociation pathways in gas molecules with the shape of the optical cycle alone, thus proving the possibility to control the outcome of such photoreactions on a sub-cycle temporal scale.
Project CyFi takes advantage of several laser technologies and phase-control concepts with the aim to advance strong-field optical tools to a conceptually new level: from adjusting the intensity and timing of a principal half-cycle to achieving a full-fledged multicolor Fourier synthesis of the optical cycle dynamics by controlling a multi-dimensional space of carrier frequencies, relative, and absolute phases. Traditional “single-color” driver fields are frustratingly limited in their capacity to optimize the outcome of strong-field interactions that involve electron re-scattering on parent ionic cores because there is no flexibility in controlling electron trajectories. The practical advantage of replacing such sinusoidal driver fields with multicolour cycle-shaped waveforms is to enable electron trajectory engineering through which the yield and spectral brightness of secondary coherent emission—such as soft X-ray and Terahertz—can be increased by orders of magnitude.
During the project, the TU Vienna team, drawing on its extensive expertise in the CEP control and methods of laser and parametric amplification of ultrashort pulses, has developed and tested a version of an optical cycle shaper for strong field applications based on a commensurate-frequency multicolor pulse synthesis. The three-color driver pulses were successfully used to drive ionization and recombination processed in gas targets to observe prominent enhancements in the spectra of above-threshold ionization electrons and in the spectra of soft X-rays emitted by high-order harmonic generation. Compared to a single-color driver scheme under identical conditions and pulse intensity, the researchers have achieved at least a six-fold increase of the spectral brightness and at least a ten-fold increase of temporal intensity of attosecond X-ray bursts. The team has achieved few-cycle multicolor driver pulses of unprecedented energies reaching 25 mJ and has demonstrated multicolor-driven HHG spectra covering the whole water window in the soft X-ray spectral region.
Using an incommensurate-frequency pulse synthesis, the CyFi project team has also succeeded in experimentally verifying its assumptions about the feasibility to generate frequency-tunable THz pulses by controlling the electron micro-currents in a laser-induced gas plasma. A self-consistent theory explaining the mechanism of such emission was developed.
Driver pulses consisting of intense optical waveforms with sculpted optical cycles were also successfully applied to demonstrate the ability to pre-determine the ionization and dissociation pathways in gas molecules with the shape of the optical cycle alone, thus proving the possibility to control the outcome of such photoreactions on a sub-cycle temporal scale.