Lasers for Accelerators R&D
Unifying photonics and accelerator physics is essential for the development of future accelerators, free electron lasers, and other scientific instruments due to increasingly synergistic advances at the cross‑section between these two fields. Laser fields are ideal agents to tailor the 6-D phase-space distribution of electron beams because they can imprint correlations with extremely high spatio-temporal precision. The Lasers for Accelerators (L4A) team serves existing facilities and disciplines at SLAC National Accelerator Laboratory and Stanford University by bringing together experts from various backgrounds in photon sciences and accelerator physics to create integrative scientific and technological advancements in quantum and nonlinear optics, accelerators, and bright x-ray sources.
R&D Projects
Ultrafast optical lasers are the primary drivers of a fast growing range of scientific and technological applications. In particular, fiber lasers have recently gained significant traction in ultrafast and nonlinear optics because of their robustness in beam delivery and capacity for high average power. We examine a variety of elementary fiber and hybrid ultrafast photon sources as well as beam delivery solutions based on integrated photonics for operations and research activities relevant to ultrafast photonics and X-ray science.
The carrier-envelope phase (CEP) is one of the most salient features of few-cycle laser pulses and ultra-stable frequency combs. The CEP refers to the relative phase relationship between the carrier (electric field) and the intensity envelope. In conventional ultrashort lasers, both linear and nonlinear factors result in shot-to-shot fluctuations of the CEP, which in the frequency domain translates to an unstable frequency comb. As a result, no single pulse exhibits the same CEP as the next in a pulse train. Because a vast number of ultrafast physical processes depend on the CEP—including nonlinear optics, quantum materials, and particle acceleration, among many others—controlling and stabilizing the CEP is of utmost importance to probe or precision-control systems in ultrafast sciences. As stable frequency combs, these properties can also be exploited for advanced Fourier-transform spectroscopies over broad spectral bandwidths, which are particularly relevant for molecular spectroscopies.
Independent photon arrival time monitoring based on spectral/spatial encoding was first demonstrated by LCLS and has been routinely used at X-ray free electron lsaer (XFEL) facilities since 2011. So far, spectral encoding has only been operating at repetition rates of up to 120 Hz at LCLS. With the anticipation of LCLS-II and LCLS-II-HE, an extension of this capability to MHz repetition rates has yet to be studied and developed with dramatically higher sensitivities. We develop cross-correlation techniques at the quantum level (e.g. single photon detection) capable of measuring stimulated processes between two ultrashort wave packets with single-digit attosecond accuracy. Quantum cross-correlators are not only relevant for attosecond metrology and synchronization of future scientific instruments but can also be used to study the response of quantum electrodynamics in quantum materials.
Laser-particle interactions lie at the heart of accelerator physics and X-ray free electron laser (XFEL) technology. In addition to long-standing challenges in photoinjectors, recent applications to XFEL seeding, compact accelerators, and ultrafast electron diffraction (UED) have highlighted the need for advanced research in new laser architectures and laser-particle interactions. One exemplary challenge in XFELs is the microbunching instability, which is known to degrade their emission performance. The longitudinal dynamics in photoinjectors and linear accelerators are highly nonlinear, thereby undermining the performance of the XFELs, such as longitudinal coherence, peak brightness, pulse druation and photon range. We investigate novel laser-based electron beam generation, shaping and conditioning schemes that can compensate for these nonlinearities to render dramatically more effective photoinjector, linear accelerator and XFEL performance, and as a result impact the vast majority UED and XFEL science applications.
The ability to produce complex spatio-temporal electric field vector distributions opens myriads of opportunities in physical, biological, and chemical sciences because photonics are often use to drive, diagnose, or manipulate states of matter. Beams with space-variant vectors and wavefronts—that is, beams with 4-D controllable orbital and spin angular momenta—exhibit unique properties such as complex optical vortices and strongly localized vector fields that can be exploited in the realms of nonlinear physical dynamics, advanced imaging and microscopy, and particle control, among many others.
At LCLS, these beams are at the heart of novel accelerator technology because they are capable of generating, controlling, and manipulating charged particle beams with unparalleled spatio-temporal precision. A large ensemble of diverse laser-driven particle manipulation schemes can reach new horizons with the ability to tune fundamental properties of the laser field on demand—such as transverse and longitudinal pulse shaping—because these directly interact and can imprint tailored micro-correlations in charged-particle beams. Fueled by this wide-ranging promise, we develop turn-key laser architectures capable of generating light with 4-D programmable structure for adaptable light-driven technologies and applications, such as on-chip accelerators and quantum optics.
Predicting and reconstructing the full real- and phase-space dimensional structure of light as it propagates through media is key to the development of ultrafast optical lasers and their applications, particularly in the case of the generation of structured light and highly nonlinear media. This effort is instrumental in assisting photon source architectural and end-to-end beam delivery design decisions.
We have developed a (2+1)-D simulation code to control and predict the near- and far-field distributions of arbitrarily defined light pulses. This set of tools, all in base MATLAB, mainly provide the ability to describe and propagate a multitude of different distributions common in laser optics. The main use is for the modeling of coherent laser combination in regularly tiled arrays and propagation through free space. However, there is also the ability to model: arbitrary tiling, Gaussian, Hermite-Gaussian, Laguerre-Gaussian fields. Additionally there is a custom genetic algorithm (GA) that can be used to optimize or reconstruct initial fields based on simulated propagated fields or on real world camera images.
