We provide a detailed account of the design and implementation of the LCLS-II photoinjector laser system, highlighting its major subsystems and innovations that enable the generation of high-energy, high-quality X-ray pulses on the attosecond timescale, crucial for advancing X-ray Free Electron Laser (XFEL) research.

We present a comprehensive overview of the development of the LCLS-II photoinjector laser system, emphasizing its key components and advancements in producing high-quality, high-energy, attoseconds X-ray pulses for X-ray Free Electron Laser science.

This paper presents a comprehensive technical overview of the Linac Coherent Light Source II (LCLS-II) photoinjector laser system, its first and foremost component. The LCLS-II photoinjector laser system serves as an upgrade to the original LCLS at SLAC National Accelerator Laboratory. This advanced laser system generates high-quality laser beams to power the LCLS-II, contributing to the instrument's unprecedented brightness, precision, and flexibility. Our discussion extends to the various subsystems that comprise the photoinjector, including the photocathode laser, laser heater, and beam transport systems. Lastly, we draw attention to the ongoing research and development infrastructure underway to enhance the functionality and efficiency of the LCLS-II, and similar X-ray free-electron laser facilities around the world, thereby contributing to the future of laser technology and its applications.

Abstract Motivated by the profound impact of laser technology on science, arising from an increase in focused light intensity by seven orders of magnitude and flashes so short electron motion is visible, this roadmap outlines the paths forward in laser technology to enable the next generation of science and applications. Despite remarkable progress, the field confronts challenges in developing compact, high-power sources, enhancing scalability and efficiency, and ensuring safety standards. Future research endeavors aim to revolutionize laser power, energy, repetition rate and precision control; to transform mid-infrared sources; to revolutionize approaches to field control and frequency conversion. These require reinvention of materials and optics to enable intense laser science and interdisciplinary collaboration. The roadmap underscores the dynamic nature of laser technology and its potential to address global challenges, propelling progress and fostering sustainable development. Ultimately, advancements in laser technology hold promise to revolutionize myriad applications, heralding a future defined by innovation, efficiency, and sustainability.

We present a thorough description of the LCLS-II photoinjector laser system, an instrument underpinning ultrafast X-ray sciences. Our presentation will highlight key components and advancements in generating high-quality, high-energy, ultrashort X-ray pulses in X-ray Free Electron Lasers.

We describe the Matter in Extreme Conditions Upgrade (MEC-U) project, co-locating kilojoule long pulse and high repetition rate petawatt lasers with LCLS in a new experimental hall at SLAC National Accelerator Laboratory.

The structural versatility of light underpins an outstanding collection of optical phenomena where both geometrical and topological states of light can dictate how matter will respond or display. Light possesses multiple degrees of freedom such as amplitude, and linear, spin angular, and orbital angular momenta, but the ability to adaptively engineer the spatio-temporal distribution of all these characteristics is primarily curtailed by technologies used to impose any desired structure to light. We demonstrate a laser architecture based on coherent beam combination offering integrated spatio-temporal field control and programmability, thereby presenting unique opportunities for generating light by design to exploit its topology.

The Linac Coherent Light Source (LCLS) X-ray Free Electron Laser (XFEL) is an open-access user facility that delivers ultrashort X-ray pulses that are nine orders of magnitude brighter than any prior source, able to probe the characteristics of matter with unprecedented spatial and temporal precision. The Matter in Extreme Conditions (MEC) instrument at LCLS combines the XFEL with high-power, short-pulse lasers to produce and study high energy density (HED) plasmas to develop the fundamental understanding of plasmas and matter in extreme environments. This has driven a remarkably rich array of high-profile scientific results with applications in fusion energy, isotope production, advanced materials, and medical and nuclear technology. The Matter in Extreme Conditions Upgrade (MEC-U) Project proposes a major upgrade to MEC that would significantly increase the power and repetition rate of the high intensity laser system to the petawatt level (PW, 1015 Watts) at 10 Hz, increase the energy of the shock-driver laser to the kilojoule level (kJ), and expand the capabilities of the MEC instrument to support groundbreaking experiments enabled by the combination of high-power lasers with the world’s brightest X-ray source.

We report the demonstration of optical compression of an electron beam and the production of controllable trains of femtosecond, soft x-ray pulses with the Linac Coherent Light Source (LCLS) free-electron laser (FEL). This is achieved by enhanced self-amplified spontaneous emission with a 2  μm laser and a dechirper device. Optical compression was achieved by modulating the energy of an electron beam with the laser and then compressing with a chicane, resulting in high current spikes on the beam which we observe to lase. A dechirper was then used to selectively control the lasing region of the electron beam. Field autocorrelation measurements indicate a train of pulses, and we find that the number of pulses within the train can be controlled (from 1 to 5 pulses) by varying the dechirper position and undulator taper. These results are a step toward attosecond spectroscopy with x-ray FELs as well as future FEL schemes relying on optical compression of an electron beam.

We report experimental results on the diffractive imaging of three-dimensionally aligned 2,5-diiodothiophene molecules. The molecules were aligned by chirped near-infrared laser pulses, and their structure was probed at a photon energy of 9.5 keV (λ ≈ 130 pm) provided by the Linac Coherent Light Source. Diffracted photons were recorded on the Cornell-SLAC pixel array detector, and a two-dimensional diffraction pattern of the equilibrium structure of 2,5-diiodothiophene was recorded. The retrieved distance between the two iodine atoms agrees with the quantum-chemically calculated molecular structure to be within 5%. The experimental approach allows for the imaging of intrinsic molecular dynamics in the molecular frame, albeit this requires more experimental data, which should be readily available at upcoming high-repetition-rate facilities.

we present the synthesis of ultrashort laser bullets with real-time adaptive and programmable field topology, including field amplitude, and linear, spin angular, and orbital angular momenta.

We design and realize an arrival time diagnostic for ultrashort X-ray pulses achieving unprecedented high sensitivity in the soft X-ray regime via cross-correlation with a ≈1550 nm optical laser. An interferometric detection scheme is combined with a multi-layer sample design to greatly improve the sensitivity of the measurement. We achieve up to 275% of relative signal change when exposed to 1.6 mJ/cm2 of soft X-rays at 530 eV, more than a hundred-fold improvement in sensitivity as compared to previously reported techniques. The resolution of the arrival time measurement is estimated to around 2.8 fs (rms). The demonstrated X-ray arrival time monitor paves the way for sub-10 fs-level timing jitter at high repetition rate X-ray facilities.

We present the new drive laser system for the photo-injector of the LCLS-II XFEL at SLAC, including the first commissioning results and challenges encountered due to high power, high repetition rate ultraviolet laser operation.

We present a carrier envelope phase (CEP) stable system capable of arbitrary intensity, phase, and spin angular momentum distributions based on the principles of free-space coherent synthesis.

We present a generalized light source architecture offering dynamic topological control with a broad ensemble of complex states of light to drive, probe or interact with quantum and nonlinear systems..

we examine an integrated laser architecture offering adaptive spatio-temporal field distribution and topology, including control over its amplitude, and linear, spin angular, and orbital angular momenta to exploit its topology.

We present the technical design of the pulsed-optical timing distribution system for LCLS-II and characterize its performance with out-of-loop measurements indicating a long-term timing stability of one femtosecond.

We present a laser architecture with programmable control of the polarization vector, transverse and longitudinal intensity, and wavefront in the near and far field as a novel tool to probe and control matter. © 2019 The Author(s)

We present a 100 kHz, sub-20 fs optical parametric chirped-pulse amplifier (OPCPA) system delivering 88.6 W average power at a center wavelength of 800 nm. The seed pulses are derived from the pump laser via white-light continuum generation and are amplified in three non-collinear OPCPA stages. The final two high-power stages are pumped with a 661 W Yb:YAG InnoSlab amplifier. A simple and robust design is used for the OPCPA system to avoid thermal effects and enhance long-term stability, resulting in excellent beam quality and high conversion efficiency. To the best of our knowledge, this is the highest average power OPCPA system reported to date.

W ELCOME to the IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS (JSTQE) Issue on Ultrafast Science & Technology. The field has seen a big highlight, since the Nobel prize in physics for 2018 was announced in high intensity lasers. The application space integrates state-of-the-art photonics techniques coming from the areas of quantum electronics, lasers, fiber optics and electro-optics to chemistry. This field continues to vastly expand with advanced developments across the entire spectrum of ultrafast applications ranging from fundamental laboratory studies to high harmonic generation, attosecond science, non-linear optics, and laser innovation. Recently developed innovative technologies have made a significant impact on ultrafast research in many areas, and is now expanding out of the realm of fundamental science research to industrial applications. In the papers included in this JSTQE Issue on UST, you will be introduced to some of the latest leading-edge developments in generating, propagating, measuring, and applications of ultrafast pulses of light. Moreover, the UST field has introduced opportunities for interdisciplinary research between physicists, chemists and engineers leading to the development of novel laser, fiber optics, and high intensity light in the midInfrared, to EUV region of the electromagnetic spectrum, which is employed in a broad range of scientific areas. The objective of this JSTQE Issue on Ultrafast Science and Technology is to highlight recent progress, challenges and trends in innovative UST developments. The papers published in this issue cover a broad range of advanced areas summarized in the following sections: High harmonic generation: Advances in generation UV, VUV, and EUV light. Including single cycle pulse synthesis. Ultrafast lasers: New materials, and mid-IR laser technology. Non-linear optics: New laser light conversion techniques and ultrafast propagation in materials. Ultrafast chemistry: Advances in techniques using ultrafast lasers for chemistry applications. These key research topics are highlighted as comprehensive overviews of the current status and future trends, as well as original results and recent developments in the field of Ultrafast Science and Technology. This issue contains 25 papers, including 8 invited and 17 contributed papers authored by well-regarded research groups and scientists, both established and emerging, from all over the world. The invited papers include overviews on recent ultrafast