High Power Laser Science and Engineering
Andreas Döpp; Matthew Streeter; Scott Feister; Hyung Taek Kim; Charlotte Palmer
Vol. , Issue , 2022
Editor(s): Andreas Döpp; Matthew Streeter; Scott Feister; Hyung Taek Kim; Charlotte Palmer
Year: 2022
Status: Call for Papers

Original manuscripts are sought to the special issue on "Future Control Systems and Machine Learning at High Power Laser Facilities" of High Power Laser Science and Engineering (HPL),

Contents 10 article(s)
Data-driven science and machine learning methods in laser–plasma physicsEditors' Pick
Andreas Döpp, Christoph Eberle, Sunny Howard, Faran Irshad, Jinpu Lin, and Matthew Streeter

Laser-plasma physics has developed rapidly over the past few decades as lasers have become both more powerful and more widely available. Early experimental and numerical research in this field was dominated by single-shot experiments with limited parameter exploration. However, recent technological improvements make it possible to gather data for hundreds or thousands of different settings in both experiments and simulations. This has sparked interest in using advanced techniques from mathematics, statistics and computer science to deal with, and benefit from, big data. At the same time, sophisticated modeling techniques also provide new ways for researchers to deal effectively with situation where still only sparse data are available. This paper aims to present an overview of relevant machine learning methods with focus on applicability to laser-plasma physics and its important sub-fields of laser-plasma acceleration and inertial confinement fusion.

High Power Laser Science and Engineering
May. 30, 2023, Vol. 11 Issue 5 05000e55 (2023)
Control systems and data management for high-power laser facilitiesEditors' Pick
Scott Feister, Kevin Cassou, Stephen Dann, Andreas Döpp, Philippe Gauron, Anthony J. Gonsalves, Archis Joglekar, Victoria Marshall, Olivier Neveu, Hans-Peter Schlenvoigt, Matthew J. V. Streeter, and Charlotte A. J. Palmer

The next generation of high-power lasers enables repetition of experiments at orders of magnitude higher frequency than what was possible using the prior generation. Facilities requiring human intervention between laser repetitions need to adapt in order to keep pace with the new laser technology. A distributed networked control system can enable laboratory-wide automation and feedback control loops. These higher-repetition-rate experiments will create enormous quantities of data. A consistent approach to managing data can increase data accessibility, reduce repetitive data-software development and mitigate poorly organized metadata. An opportunity arises to share knowledge of improvements to control and data infrastructure currently being undertaken. We compare platforms and approaches to state-of-the-art control systems and data management at high-power laser facilities, and we illustrate these topics with case studies from our community.

High Power Laser Science and Engineering
Jun. 15, 2023, Vol. 11 Issue 5 05000e56 (2023)
Versatile tape-drive target for high-repetition-rate laser-driven proton acceleration
N. Xu, M. J. V. Streeter, O. C. Ettlinger, H. Ahmed, S. Astbury, M. Borghesi, N. Bourgeois, C. B. Curry, S. J. D. Dann, N. P. Dover, T. Dzelzainis, V. Istokskaia, M. Gauthier, L. Giuffrida, G. D. Glenn, S. H. Glenzer, R. J. Gray, J. S. Green, G. S. Hicks, C. Hyland, M. King, B. Loughran, D. Margarone, O. McCusker, P. McKenna, C. Parisuaña, P. Parsons, C. Spindloe, D. R. Symes, F. Treffert, C. A. J. Palmer, and Z. Najmudin

We present the development and characterization of a high-stability, multi-material, multi-thickness tape-drive target for laser-driven acceleration at repetition rates of up to 100 Hz. The tape surface position was measured to be stable on the sub-micrometre scale, compatible with the high-numerical aperture focusing geometries required to achieve relativistic intensity interactions with the pulse energy available in current multi-Hz and near-future higher repetition-rate lasers ( $>$ kHz). Long-term drift was characterized at 100 Hz demonstrating suitability for operation over extended periods. The target was continuously operated at up to 5 Hz in a recent experiment for 70,000 shots without intervention by the experimental team, with the exception of tape replacement, producing the largest data-set of relativistically intense laser–solid foil measurements to date. This tape drive provides robust targetry for the generation and study of high-repetition-rate ion beams using next-generation high-power laser systems, also enabling wider applications of laser-driven proton sources.

High Power Laser Science and Engineering
Mar. 21, 2023, Vol. 11 Issue 2 02000e23 (2023)
Hyperspectral compressive wavefront sensing
Sunny Howard, Jannik Esslinger, Robin H. W. Wang, Peter Norreys, and Andreas Döpp

Presented is a novel way to combine snapshot compressive imaging and lateral shearing interferometry in order to capture the spatio-spectral phase of an ultrashort laser pulse in a single shot. A deep unrolling algorithm is utilized for snapshot compressive imaging reconstruction due to its parameter efficiency and superior speed relative to other methods, potentially allowing for online reconstruction. The algorithm’s regularization term is represented using a neural network with 3D convolutional layers to exploit the spatio-spectral correlations that exist in laser wavefronts. Compressed sensing is not typically applied to modulated signals, but we demonstrate its success here. Furthermore, we train a neural network to predict the wavefronts from a lateral shearing interferogram in terms of Zernike polynomials, which again increases the speed of our technique without sacrificing fidelity. This method is supported with simulation-based results. While applied to the example of lateral shearing interferometry, the methods presented here are generally applicable to a wide range of signals, including Shack–Hartmann-type sensors. The results may be of interest beyond the context of laser wavefront characterization, including within quantitative phase imaging.

High Power Laser Science and Engineering
Mar. 21, 2023, Vol. 11 Issue 3 03000e32 (2023)
Optimization and control of synchrotron emission in ultraintense laser–solid interactions using machine learningOn the Cover
J. Goodman, M. King, E. J. Dolier, R. Wilson, R. J. Gray, and P. McKenna

The optimum parameters for the generation of synchrotron radiation in ultraintense laser pulse interactions with planar foils are investigated with the application of Bayesian optimization, via Gaussian process regression, to 2D particle-in-cell simulations. Individual properties of the synchrotron emission, such as the yield, are maximized, and simultaneous mitigation of bremsstrahlung emission is achieved with multi-variate objective functions. The angle-of-incidence of the laser pulse onto the target is shown to strongly influence the synchrotron yield and angular profile, with oblique incidence producing the optimal results. This is further explored in 3D simulations, in which additional control of the spatial profile of synchrotron emission is demonstrated by varying the polarization of the laser light. The results demonstrate the utility of applying a machine learning-based optimization approach and provide new insights into the physics of radiation generation in laser–foil interactions, which will inform the design of experiments in the quantum electrodynamics (QED)-plasma regime.

High Power Laser Science and Engineering
Feb. 14, 2023, Vol. 11 Issue 3 03000e34 (2023)
Automated control and optimization of laser-driven ion acceleration
B. Loughran, M. J. V. Streeter, H. Ahmed, S. Astbury, M. Balcazar, M. Borghesi, N. Bourgeois, C. B. Curry, S. J. D. Dann, S. DiIorio, N. P. Dover, T. Dzelzainis, O. C. Ettlinger, M. Gauthier, L. Giuffrida, G. D. Glenn, S. H. Glenzer, J. S. Green, R. J. Gray, G. S. Hicks, C. Hyland, V. Istokskaia, M. King, D. Margarone, O. McCusker, P. McKenna, Z. Najmudin, C. Parisuaña, P. Parsons, C. Spindloe, D. R. Symes, A. G. R. Thomas, F. Treffert, N. Xu, and C. A. J. Palmer

The interaction of relativistically intense lasers with opaque targets represents a highly non-linear, multi-dimensional parameter space. This limits the utility of sequential 1D scanning of experimental parameters for the optimization of secondary radiation, although to-date this has been the accepted methodology due to low data acquisition rates. High repetition-rate (HRR) lasers augmented by machine learning present a valuable opportunity for efficient source optimization. Here, an automated, HRR-compatible system produced high-fidelity parameter scans, revealing the influence of laser intensity on target pre-heating and proton generation. A closed-loop Bayesian optimization of maximum proton energy, through control of the laser wavefront and target position, produced proton beams with equivalent maximum energy to manually optimized laser pulses but using only 60% of the laser energy. This demonstration of automated optimization of laser-driven proton beams is a crucial step towards deeper physical insight and the construction of future radiation sources.

High Power Laser Science and Engineering
Mar. 27, 2023, Vol. 11 Issue 3 03000e35 (2023)
Laser pulse shape designer for direct-drive inertial confinement fusion implosionsEditors' Pick
Tao Tao, Guannan Zheng, Qing Jia, Rui Yan, and Jian Zheng

Pulse shaping is a powerful tool for mitigating implosion instabilities in direct-drive inertial confinement fusion (ICF). However, the high-dimensional and nonlinear nature of implosions makes the pulse optimization quite challenging. In this research, we develop a machine-learning pulse shape designer to achieve high compression density and stable implosion. The facility-specific laser imprint pattern is considered in the optimization, which makes the pulse design more relevant. The designer is applied to the novel double-cone ignition scheme, and simulation shows that the optimized pulse increases the areal density expectation by 16% in one dimension, and the clean-fuel thickness by a factor of four in two dimensions. This pulse shape designer could be a useful tool for direct-drive ICF instability control.

High Power Laser Science and Engineering
Apr. 26, 2023, Vol. 11 Issue 3 03000e41 (2023)
Tango Controls and data pipeline for petawatt laser experiments
Nils Weiße, Leonard Doyle, Johannes Gebhard, Felix Balling, Florian Schweiger, Florian Haberstroh, Laura D. Geulig, Jinpu Lin, Faran Irshad, Jannik Esslinger, Sonja Gerlach, Max Gilljohann, Vignesh Vaidyanathan, Dennis Siebert, Andreas Münzer, Gregor Schilling, Jörg Schreiber, Peter G. Thirolf, Stefan Karsch, and Andreas Döpp

The Centre for Advanced Laser Applications in Garching, Germany, is home to the ATLAS-3000 multi-petawatt laser, dedicated to research on laser particle acceleration and its applications. A control system based on Tango Controls is implemented for both the laser and four experimental areas. The device server approach features high modularity, which, in addition to the hardware control, enables a quick extension of the system and allows for automated data acquisition of the laser parameters and experimental data for each laser shot. In this paper we present an overview of our implementation of the control system, as well as our advances in terms of experimental operation, online supervision and data processing. We also give an outlook on advanced experimental supervision and online data evaluation – where the data can be processed in a pipeline – which is being developed on the basis of this infrastructure.

High Power Laser Science and Engineering
Feb. 21, 2023, Vol. 11 Issue 4 04000e44 (2023)
Applications of object detection networks in high-power laser systems and experimentsOn the Cover
Jinpu Lin, Florian Haberstroh, Stefan Karsch, and Andreas Döpp

The recent advent of deep artificial neural networks has resulted in a dramatic increase in performance for object classification and detection. While pre-trained with everyday objects, we find that a state-of-the-art object detection architecture can very efficiently be fine-tuned to work on a variety of object detection tasks in a high-power laser laboratory. In this paper, three exemplary applications are presented. We show that the plasma waves in a laser–plasma accelerator can be detected and located on the optical shadowgrams. The plasma wavelength and plasma density are estimated accordingly. Furthermore, we present the detection of all the peaks in an electron energy spectrum of the accelerated electron beam, and the beam charge of each peak is estimated accordingly. Lastly, we demonstrate the detection of optical damage in a high-power laser system. The reliability of the object detector is demonstrated over 1000 laser shots in each application. Our study shows that deep object detection networks are suitable to assist online and offline experimental analysis, even with small training sets. We believe that the presented methodology is adaptable yet robust, and we encourage further applications in Hz-level or kHz-level high-power laser facilities regarding the control and diagnostic tools, especially for those involving image data.

High Power Laser Science and Engineering
Jan. 13, 2023, Vol. 11 Issue 1 010000e7 (2023)
Laser wakefield accelerator modelling with variational neural networksEditors' Pick
M. J. V. Streeter, C. Colgan, C. C. Cobo, C. Arran, E. E. Los, R. Watt, N. Bourgeois, L. Calvin, J. Carderelli, N. Cavanagh, S. J. D. Dann, R. Fitzgarrald, E. Gerstmayr, A. S. Joglekar, B. Kettle, P. Mckenna, C. D. Murphy, Z. Najmudin, P. Parsons, Q. Qian, P. P. Rajeev, C. P. Ridgers, D. R. Symes, A. G. R. Thomas, G. Sarri, and S. P. D. Mangles

A machine learning model was created to predict the electron spectrum generated by a GeV-class laser wakefield accelerator. The model was constructed from variational convolutional neural networks, which mapped the results of secondary laser and plasma diagnostics to the generated electron spectrum. An ensemble of trained networks was used to predict the electron spectrum and to provide an estimation of the uncertainty of that prediction. It is anticipated that this approach will be useful for inferring the electron spectrum prior to undergoing any process that can alter or destroy the beam. In addition, the model provides insight into the scaling of electron beam properties due to stochastic fluctuations in the laser energy and plasma electron density.

High Power Laser Science and Engineering
Jan. 06, 2023, Vol. 11 Issue 1 010000e9 (2023)
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