Structures, dynamics, and phenomena in the chemical and biological sciences are based on equilibrium descriptions in the absence of an external stimulus. However, an ever-growing swathe of processes involving energetic stimuli – for example, light excitation in photocatalysis or strong-field THz radiation –drive these systems out of equilibrium to render new states or behavioral dynamics along with new properties in health-related applications. In this talk, we will anchor ultrafast terahertz excitation as a generalized approach to theoretically and experimentally study basic nonequilibrium states of water and water-based systems to orchestrate solvation (bio)chemistry to capable of tackling real-world societal challenges, such as paving the path to water remediation of environmental pollutants and understanding biological function of proteins under external stimuli for personalized medicine.
The advancement of laser technology has greatly increased the intensity of focused light over the past seventy years. This has allowed for the study of ultrafast events and has opened up new fields of science and various applications in society. From understanding atomic processes to manipulating particle beams, lasers have had a significant impact in scientific research. However, many laser technologies are now reaching their limits after decades of progress. During this talk, we will present recent results leveraging attosecond-level frequency comb stabilty, such as heterodyne and homodyne detection techniques for quantum sensing applications. We will also review and address the challenges on emerging technologies from first principles quantum electrodynamics to materialize both large-scale facility and compact hard X-ray sources exhibiting attosecond pulse durations to probe electronic dynamics with atomic specificity simultaneously.
The ability to general strong-field THz radiation has opened the possibility to study nonequilibrium structural and energetic dynamics in chemistry, biology, condensed matter physics, and a host of other quantum phenomena in ultrafast timescales. In this talk, we will review some of these enabling THz technologies and their application to emerging research in ultrafast quantum biochemistry and quantum information science using state-of-the-art probes, spanning ultrashort X-ray, optical, and free electron probes. The resulting knowledge and methodologies are poised to become essential components for addressing critical challenges and needs ranging from personalized medicine to approaches in environmental and toxicity remediation
We report on the design of a tunable, near-infrared (NIR) femtosecond noncollinear optical parametric amplifier (OPA) seeded by gain-managed nonlinear amplified1 parabolic pulses. In our numerical simulations, we achieve signal and idler amplification bandwidths between 1000-1180 nm and 914-1062 nm; the second harmonic of these pulses corresponds directly to the visible spectrum. This appreciable value is due to the high spectral energy density of our seed pulses. Fiber-amplified pulses thus present a method to engineer efficient OPA systems that can operate at high-average powers in the NIR and visible.
The next generation of ultra-bright photoemission sources may offer opportunities to enhance our understanding of fundamental spatiotemporal scales. However, modeling photoemission and laser shaping systems precisely and efficiently is difficult due to the numerous interdependent linear and nonlinear processes involved and significant variations in modeling frameworks. Here, we present a new machine learning-based framework for photoemission laser systems and dynamic laser shaping. To showcase the effectiveness of our approach in system optimization, reverse engineering, and design. Our framework is designed to facilitate precise adaptive temporal shaping, including the generation of longitudinally flat-top or periodically-modulated pulses, through integration with four-wave mixing.
Free-electron laser beam quality can be degraded due to microbunching instability (MBI) caused by collective quantum electrodynamic effects. A Laguerre-Gaussian mode laser profile has been shown to significantly reduce MBI compared to the standard Gaussian profile under ideal conditions. However, practical limitations of accelerators significantly hinder the Laguerre-Gaussian profile’s performance. We propose the use of a Bessel-Gaussian mode profile for laser heating. We model the interaction between the laser heater and e-beam with various spatial profiles and compare the Bessel-Gaussian with the Gaussian and Laguerre-Gaussian modes. We showcase the Bessel-Gaussian beam’s immunity to jitter and consistent suppression of MBI.
Temporal shaping of picosecond duration pulses is challenging due to limitations of direct shaping with electro-optical technologies or spectral shaping because of limited spectral content. We present an experimental implementation of a non-collinear sum frequency generation scheme wherein picosecond duration pulses with tailored temporal profiles are derived from femtosecond pulses with modified spectral phase. We demonstrate temporally shaped pulses with >20 ps duration, flat-top profile, and near transform-limited spectral content while maintaining upwards of 40% conversion efficiency. Additionally, we provide a framework for extending this technique to arbitrary temporal profiles and wavelengths.
A full start-to-end software (S2E) model of a laser system– including a mode-locked oscillator,
chirped pulse amplification shaper, and nonlinear upconversion– can help expand high power laser system designs routinely tackled with human-centered methodologies. S2E models can even enable reverse engineering of a laser system, allow for more streamlined exploration of parameter spaces for experimental setups, or train machine learning models for optimization and tuning of these systems. We present a generalized S2E model targeted at generating data of the photoinjector laser system at SLAC’s LCLS-II for training neural networks for optimization and, eventually, active tuning of the photoinjector.
The lasers and conventional optics used in charged-particle beam x-ray free electron laser photo-injectors are designed using fundamentally the same techniques for decades. We present a novel method for the generation and conditioning of the UV laser used for electron generation via photoemission that can enhance electron beam and X-ray performance. Additionally, we discuss laser-based spatio-temporal shaping and conditioning of electron beam phase space in order to selectively promote lasing operational modes.
Ultralow phase-noise mode-locked lasers are crucial for real-world applications. We present two accomplishments: (1) short-term FF CEP stabilization of a SESAM mode-locked Er:Yb:glass laser at 1.55 um with timing jitter below 3 as (1-3 MHz) and (2) a hybrid solution adding a FB technique addressing slowly varying sources of interference to the FF system that demonstrates 75 hours of stabilization with a minimally detrimental effect amounting to a timing jitter of 11 as.
The structuring of laser light with non-diffracting vector distributions, optical vortices, or high angular momentum are being increasing exploited. We present a system for the synthesis of these arbitrary intensity and phase profiles through a number of carrier-envelope-phase stabilized coherent frequency and spatial combs. Adjusting the differences between adjacent combs allows synthesis of a combined field which can be structured, directed, and improved in the presence of propagation noise. Additionally, we present a method for the optimization of such systems in free space with a Fourier optics based genetic algorithm that converges to <π/10 accuracy of the initial parameters.
In this work we present the application of a 2D single grating wavefront sensor to align and characterize the 100 nm focus at the Coherent X-ray Imaging (CXI) endstation at the Linac Coherent Light Source (LCLS). The results agree well with a model of the system, indicating that the mirrors perform as designed when alignment is optimized. In addition, a comparison with the imprint technique confirms the validity of the results, which showed that wavefront-based alignment resulted in negligible astigmatism. Analysis of the retrieved focus profile indicates that intensities <1021 W=cm2 are achievable with currently available LCLS beam parameters and optimal mirror alignment.
Liquid Crystal on Silicon (LCoS) Spatial Light Modulators (SLMs) are used as programmable adaptive optical elements1,2,3 in many applications involving high power lasers. In some cases, LCoS SLMs may be exposed to laser radiation that can cause permanent, irreparable damage to the SLM. The damage arises from a number of parameters including laser wavelength, pulse duration, pulse repetition rate, beam diameter, spatial profile, temporal profile, and even angle of incidence. This paper is an introduction and practical guide to understanding laser damage mechanisms and expected damage threshold levels for LCoS SLMs.
KEYWORDS: Power meters, X-rays, Free electron lasers, Sensors, Laser development, Reflectivity, Mirrors, Temperature metrology, Liquid crystal lasers, Stanford Linear Collider
For the LCLS-II instruments we are developing laser power meters as compact intensity monitors that can operate at soft and tender X-ray photon energies. There is a need to monitor the relative X-ray intensity at various locations along an X-ray FEL beamline in order to observe a possible decrease in the reflectivity of X-ray mirrors. In addition for experiments, it is valuable to know the absolute intensity at the sample. There are two types of laser power meters based on thermopile and pyroelectric sensors. The thermopile power meters measure an average temperature and are compatible with the high repetition rates of LCLS-II. Pyroelectric power meters provide a pulse-by-pulse response. Ultra-high vacuum compatibility is being tested by residual gas analysis. An in-house development beamtime is being conducted at the LCLS SXR instrument. Measurements using both thermopile and pyroelectric power meters will be conducted at a set of photon energies in the soft X-ray range. The detectors’ response will be compared with the gas monitor detector installed at the SXR instrument.
We present a method for the optimization of the illumination in soft x-ray (SXR) full-field microscopes. The method
consists of imaging a single periodic grating with a period large compared to the wavelength of the illumination and
obtaining its Fourier spectrum in two orthogonal directions. The analysis of the cut-off frequency along the two
perpendicular directions allows the identification of angled illumination, which can be corrected in-situ by using the
Fourier analysis iteratively. The ability to characterize the illumination conditions and aberrations in the EUV/SXR
microscopes with a fast and simple analysis is critical to achieve the best quality images with the highest spatial
resolution.
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