SLAC’s LCLS-II is pioneering high-repetition-rate attosecond X-ray science, enabling new opportunities to optimize X-ray generation by controlling the electron beam at its source—the photoinjector. LCLS-II employs a 20 ps Gaussian UV laser pulse to drive the photocathode, with an added narrow modulation to induce microbunching for extended modes.* Recent advances in laser pulse shaping and frequency upconversion now allow for more sophisticated tailoring of the electron beam at the injector. We present a novel approach using spectral amplitude and phase shaping of the IR laser, followed by dispersion-controlled nonlinear synthesis—relying on phase-modulated noncollinear sum-frequency generation—for UV upconversion.** This enables diverse UV temporal profiles, including flattop and double/triple spikes, offering new degrees of freedom for shaping. Preliminary results from LCLS-II beam time show these modulations produce effective downstream perturbations to the electron bunch at the undulators, demonstrating feasibility for programmable bunch formation. We are integrating this shaping into a start-to-end simulation framework,*** enabling digital twin modeling of the XFEL chain—from photoinjector laser to X-ray output—laying the groundwork for fully tunable, end-to-end optimized, application-specific X-ray pulses.

Electron dynamics in molecules occur on attosecond timescales and drive fundamental processes such as photosynthesis, catalysis, and chemical bond transformations. Understanding these phenomena requires tools with both high temporal resolution and the capability to probe molecular dynamics at high repetition rates. Here, we present the first single-shot measurements of attosecond soft x-ray pulses at the superconducting LCLS-II accelerator. Using an angle-resolving electron time-of-flight spectrometer, we perform angular streaking measurements with high energy and angular resolution, enabling a complete reconstruction of the spatial and temporal profiles of the pulses. These measurements showcase the attosecond science capabilities of LCLS-II at unprecedented repetition rates and provide the foundation for controlling and shaping x-ray pulses to study ultrafast dynamics in complex systems with precision.

We report the generation of single spike hard x-ray pulses at the Linac Coherent Light Source enabled by temporal shaping of the photocathode laser. The pulses were produced with typical pulse energies of 10 uJ and full-width at half-maximum spectral bandwidths averaging 30 eV, corresponding to a 60 attosecond Fourier-limited pulse duration. These pulses open new doors in electronic-damage-free probing of ultrafast phenomena and, eventually, attosecond hard x-ray scattering experiments. We discuss progress towards characterization of the pulses in the time domain using hard x-ray angular streaking and a hard x-ray split and delay device.

The LCLS-II upgrade has expanded the capabilities of the Linac Coherent Light Source (LCLS), extending the deliverable photon energy range and increasing the repetition rate from 120 Hz to a maximum of 1 MHz. Here we report the development of attosecond X-ray science capabilities at the LCLS-II, including the commissioning of beam shaping methods for attosecond pulse generation, and the demonstration, characterization, and delivery of advanced attosecond XFEL modes at high repetition rates. We used the photocathode modulation method$*$ at LCLS-II to generate single-spike pulses with up to 10s uJ pulse energy. These attosecond pulses are characterized at the TMO instrument with the angular streaking technique$**$. Furthermore, we demonstrated advanced modes such as spectrotemporally shaped attosecond pulses$***$ and pump/probe attosecond pulse pairs. These capabilities have been delivered at a repetition rate of up to 33 kHz, enabling the next generation of ultrafast experiments at XFELs.

SLAC’s LCLS-II is pioneering high-repetition-rate attosecond X-ray science, enabling new opportunities to optimize X-ray generation by controlling the electron beam at its source—the photoinjector. LCLS-II employs a 20 ps Gaussian UV laser pulse to drive the photocathode, with an added narrow modulation to induce microbunching for extended modes.* Recent advances in laser pulse shaping and frequency upconversion now allow for more sophisticated tailoring of the electron beam at the injector. We present a novel approach using spectral amplitude and phase shaping of the IR laser, followed by dispersion-controlled nonlinear synthesis—relying on phase-modulated noncollinear sum-frequency generation—for UV upconversion.** This enables diverse UV temporal profiles, including flattop and double/triple spikes, offering new degrees of freedom for shaping. Preliminary results from LCLS-II beam time show these modulations produce effective downstream perturbations to the electron bunch at the undulators, demonstrating feasibility for programmable bunch formation. We are integrating this shaping into a start-to-end simulation framework,*** enabling digital twin modeling of the XFEL chain—from photoinjector laser to X-ray output—laying the groundwork for fully tunable, end-to-end optimized, application-specific X-ray pulses.

Electron dynamics in molecules occur on attosecond timescales and drive fundamental processes such as photosynthesis, catalysis, and chemical bond transformations. Understanding these phenomena requires tools with both high temporal resolution and the capability to probe molecular dynamics at high repetition rates. Here, we present the first single-shot measurements of attosecond soft x-ray pulses at the superconducting LCLS-II accelerator. Using an angle-resolving electron time-of-flight spectrometer, we perform angular streaking measurements with high energy and angular resolution, enabling a complete reconstruction of the spatial and temporal profiles of the pulses. These measurements showcase the attosecond science capabilities of LCLS-II at unprecedented repetition rates and provide the foundation for controlling and shaping x-ray pulses to study ultrafast dynamics in complex systems with precision.

We report the generation of single spike hard x-ray pulses at the Linac Coherent Light Source enabled by temporal shaping of the photocathode laser. The pulses were produced with typical pulse energies of 10 uJ and full-width at half-maximum spectral bandwidths averaging 30 eV, corresponding to a 60 attosecond Fourier-limited pulse duration. These pulses open new doors in electronic-damage-free probing of ultrafast phenomena and, eventually, attosecond hard x-ray scattering experiments. We discuss progress towards characterization of the pulses in the time domain using hard x-ray angular streaking and a hard x-ray split and delay device.

X-ray free-electron lasers have opened new frontiers in attosecond science thanks to their high pulse energy compared to traditional table top sources. To date, most attosecond experiments performed at XFELs have been impulsive, with the impinging x-ray pulses being much shorter than the timescales being studied. We present a method for attosecond pulse shaping which enables us to move beyond simple observation of ultrafast dynamics towards coherent control of quantum systems on sub-femtosecond timescales. We present experimental evidence of phase locked attosecond pulse trains from the LCLS-II. We conclude by presenting recent experiments utilizing mutually coherent pulse pairs with controllable temporal and spectral delay to launch controllable coherent electronic wavepackets in molecular systems.