Yudong Yang

Toward Waveform Nonlinear Optics Using Multimillijoule Sub-Cycle Waveform Synthesizers

Waveform nonlinear optics aims to study and control the nonlinear interactions of matter with extremely short optical waveforms custom-tailored within a single cycle of light. Different technological routes to generate such multimillijoule sub-optical-cycle waveforms are currently pursued, opening up unprecedented opportunities in attoscience and strong-field physics. Here, we discuss the experimental schemes, introduce the technological challenges, and present our experimental results on high-energy sub-cycle optical waveform synthesis based on (1) parametric amplification and (2) induced-phase modulation in a two-color-driven gas-filled hollow-core fiber compressor. More specifically, for (1), we demonstrate a carrier-envelope-phase (CEP)-stable, multimillijoule three-channel parametric waveform synthesizer generating a >2-octave-wide spectrum (0.52-2.4 μm). After two amplification stages, the combined 125-μJ output supports 1.9-fs FWHM waveforms; energy scaling to >2 mJ is achieved after three amplification stages. FROG pulse characterization of all three second-stage outputs demonstrates the feasibility to recompress all three channels simultaneously close to the Fourier limit and shows the flexibility of our intricate dispersion management scheme for different experimental situations. For (2), we generate CEP-stable 1.7-mJ waveforms covering 365-930 nm (measured at 1% of the peak intensity) obtained from induced-phase modulation in a two-color-driven gas-filled hollow-core fiber. Using custom-designed double-chirped mirrors and a UV spatial light modulator will permit compression close to the 0.9-fs FWHM transform limit. These novel sources will become versatile tools for controlling strong-field interactions in matter and for attosecond pump-probe spectroscopy using VIS/IR and XUV/soft-X-ray pulses.

High-dynamic-range arrival time control for flexible, accurate and precise parametric sub-cycle waveform synthesis

We introduce a simple all-inline variation of a balanced optical cross-correlator (BOC) that allows to measure the arrival time difference (ATD), over the full Nyquist bandwidth, with increased common-mode rejection and long-term stability. An FPGA-based signal processing unit allows for real-time signal normalization and enables locking to any setpoint with an unprecedented accuracy of 0.07 % within an increased ATD range of more than 400 fs, resulting in attosecond resolution locking. The setup precision is verified with an out-of-loop measurement to be less than 80 as residual jitter paving the way for highly demanding applications such as parametric waveform synthesizers.

Ellipticity dependence of higher-order harmonics in solids: Unraveling the interplay between intraband and interband dynamics

Recently, we introduced an ab-initio time-dependent density-functional theory (TDDFT) framework that allows us to investigate the coupled interplay between the interband and intraband mechanisms of high-harmonic generation (HHG) from solids [1] without making a-priori model assumptions or strong approximations. Here, using HHG experiments on bulk silicon samples combined with TDDFT simulations, we study the complex physics underlying anisotropic harmonic emission, as reported by You et al. [2] for the strongly anisotropic ellipticity dependence of the 19th harmonic (HH19) generated in bulk MgO. In [2], the observed anisotropy was explained with real-space trajectories in a 2D one-band model including scattering from neighboring atomic sites. Our TDDFT simulations [3] and HHG experiments reveal that the various higher-harmonic orders generated in solids exhibit qualitatively different sensitivity to driver-pulse ellipticity ε (not displayed here), resulting from a different response of intraband and interband dynamics [3], in contradiction with the model proposed in [2]. In fact, band-structure and joint-density-of-states (JDOS) effects become important [1].

Shot-to-shot and long-term CEP-stable front-end for a parallel optical waveform synthesizer

We present a highly automated front-end of a Ti:Sa-based optical waveform synthesizer capable of driving multiple supercontinua with stable and controlled carrier-envelope phases. The remarkable CEP-stability of 217 mrad rms single-shot will allow shot-to-shot and long-term stable waveform synthesis.

High-dynamic-range relative arrival time measurement for accurate and precise parametric waveform synthesis

We introduce an all-inline scheme for relative timing measurement of ultrabroadband pulses, featuring FPGA-based detection/feedback. High common-mode rejection and long-term stability were validated by out-of-loop measurement, paving the way for ultrabroadband optical parametric waveform synthesis.

Orthogonal control for stable parallel waveform synthesis

We present a control scheme for parallel optical parametric waveform synthesizers. Orthogonalization of the relative arrival time and relative phase between all individual channels promises to achieve shot-to-shot stable and controlled ultra-broadband pulse synthesis.

Two-octave-wide dispersive mirrors based on dual-adiabatic-matching structures

An unprecedented chirped mirror system allowing smooth dispersion control over 2-octave bandwidth is demonstrated based on dual-adiabatic-matching (DAM) structures. Advanced designs for ultra-broadband dispersive optics are provided and discussed.