Optical waveform synthesizer and its application to high-harmonic generation

Abstract

Over the last decade, the control of atomic-scale electronic motion by optical fields strong enough to mitigate the atomic Coulomb potential has broken tremendous new ground with the advent of phase-controlled high-energy few-cycle pulse sources. Further investigation and control of these physical processes, including high-harmonic generation, ask for the capability of waveform shaping on sub-cycle time scales, which requires a fully phase-controlled multiple-octave-spanning spectrum. In this paper, we present a light source that enables sub-cycle waveform shaping with a two-octave-spanning spectrum and 15 µJ pulse energy based on coherent synthesis of pulses with different spectra, or wavelength multiplexing. The synthesized pulse has its shortest high-field transient lasting only 0.8 cycles (amplitude FWHM) of the centroid frequency. The benefit of the approach lies in its modular design and scalability in both bandwidth and pulse energy. Full phase control allows for the synthesis of any optical waveform supported by the amplified spectrum. A numerical study shows the uniqueness of the light source for direct isolated soft-x-ray pulse generation based on high-harmonic generation, greatly reducing and eventually even eliminating the need for gating techniques or spectral filtering. The demonstrated system is the prototype of a class of novel optical tools for attosecond control of strong-field physics experiments.

Multi-mJ parametric synthesizer generating two-octave-wide optical waveforms

“…We generate a CEP-stable continuum (0.5-2.5 µm) [7] by white-light generation in a YAG crystal pumped by the second harmonic (1.06 µm) of the CEP-stable idler of a NIR OPA. The continuum is split with custom-designed dichroic beam splitters (which will also be used for the final beam recombination) and seeds three OPA channels, a VIS non-collinear OPA (NOPA), a NIR and an IR degenerate OPA (DOPA) channel, pumped by the pulses at 0.8 µm (IR DOPA) and its second harmonic at 0.4 µm Shaobo Fang, 1,3 for the VIS NOPA, NIR DOPA and IR DOPA, respectively). After parametric amplification, the three OPA channel outputs can individually be recompressed using custom-tailored double-chirped mirrors (DCMs).…”

“…In our earlier works, we already demonstrated coherent pulse synthesis between ultrabroadband 870-nm and 2.15-µm pulses based on optical parametric chirped-pulse amplification (OPCPA) resulting in a 15-µJ sub-cycle waveform [2,3] and also between two optical parametric amplifiers (OPAs) with 1-2 µJ energy each [4]. Here, we present our ongoing development of a novel multi-mJ 3-channel parametric synthesizer (shown in Fig.…”

“…However, the energy throughput of such hollow-core fiber compressors is limited by ionization losses in the gas medium, thus preventing further energy upscaling to the (multi-)mJ level, which is required for many interesting applications in attosecond science. In contrast, parametric synthesizers [2][3][4][5][6][7] do not face an energy-scaling bottleneck, and spectral extension into the mid-IR region is particularly appealing for the realization of bright coherent tabletop high-harmonic sources in the waterwindow and keV X-ray region [8,9].…”

Examining resonant inelastic spontaneous scattering of classical Laguerre-Gauss beams from molecules

“…[22] While some theoretical studies show the possibility of HHG to provide higher energy shaped pulses for coherent control, experiments have yet to confirm these predictions. [23,24] By varying the frequency and mode of the incident field and the vibrational frequency of interest, researchers may be able control the resonant x-ray scattering intensity and spectra excited in the energy region of many core electronic transitions via the mechanisms explored in this study. Active and systematic control over the scattering intensity provides new ways to attain information about the electronic structure, dynamics and reactivity of complex molecules.…”

Macroscopic study and control of high-order harmonic and attosecond pulse generation in noble gases

“…Recent development in ultrashort laser pulse generation yielded a tool that gets close to this goal, these are the light field synthesizers [172,173]. Such a device is based on the spectral separation of laser radiation to 3 or more interferometer channels where amplitudes, CEP values and relative delays are independently adjustable.…”