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16 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

High Harmonic Generation Seeding Echo-Enabled Harmonic Generation toward a Storage Ring-Based Tender and Hard X-ray-Free Electron Laser

To align with the global trend of integrating synchrotron light source (SLS) and free electron laser (FEL) facilities on one site, in line with examples such as SPring-8 and SACLA in Japan and ELETTRA and FERMI in Italy, we actively explore FEL options leveraging the ultralow-emittance electron beam of the NSLS-II upgrade. These options show promising potential for synergy with storage ring (SR) operations, thereby significantly enhancing our facility’s capabilities. Echo-enabled harmonic generation (EEHG) is well-suited to SR-based FELs, and has already been demonstrated with the capability of generating extremely narrow bandwidth as well as high brightness, realized using diffraction-limited short pulses in transverse planes and Fourier transform-limited bandwidth in the soft X-ray spectrum. However, regarding a conventional EEHG scheme, the combination of the shortest seed laser wavelength (256 nm) and highest harmonic (200) sets the short wavelength limit to λ = 1.28 nm. To further extend the short wavelength limit down to the tender and hard X-ray region, a vital option is to shorten the seed laser wavelength. Thanks to recent advances in high harmonic generation (HHG), packing 10 9 photons at one harmonic within a few-femtosecond pulse could turn such a novel HHG source into an ideal seeding for EEHG. Thus, compared to the cascaded EEHG, the HHG seeding option could not only lower the cost, but also free the SR space for accommodating more user beamlines. Moreover, to mitigate the SASE background noise on the sample and detector, we combine the HHG seeding EEHG with the crab cavity short pulse scheme for maximum benefit.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Toward fully coherent soft x-ray free-electron laser via echo-enabled harmonic generation in fourth generation synchrotron light sources

Having previously reported on bunching via echo-enabled harmonic generation (EEHG) as an effective way to improve the longitudinal coherence in the NSLS-II storage ring [X. Yang et al., Sci. Rep. 12, 9437 (2022)], we demonstrate that this EEHG scheme can be easily adopted to any fourth generation diffraction-limited synchrotron light source with significant benefits. The advantage of the scheme is that it requires no change of the lattice and is fully compatible with other beamlines. Since the EEHG performance is mainly determined by the momentum compaction, beam emittances, and beta functions of a SR lattice, we have identified these crucial parameters and successfully built a generalized model, which can predict the performance of nearly any SLS. Regarding the fourth generation SLSs, momentum compactions are often significantly smaller; thus, to cover the x rays with a photon energy of up to 1 keV, we utilize a specific design, including a 250 nm seed-laser wavelength. Our model predicts that for most of the current and future fourth generation SLSs, the EEHG scheme can produce significant prebunching up to harmonic 200 and, thus, generate a few MW scale peak power at 1.25 nm wavelength.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Optimization of echo-enabled harmonic generation toward coherent EUV and soft X-ray free-electron laser at NSLS-II

Prebunching via echo-enabled harmonic generation (EEHG) is an efficient way to reduce the radiator length and improve the longitudinal coherence as well as output stability in storage-ring-based free-electron lasers. We propose a conceptual design, which uses two straight sections to seed coherent extreme-ultraviolet (EUV) and soft X-ray emission with nearly MHz repetition rate. To take the large energy spread (10 –3 ) of a storage ring into account and utilize the existing bending magnets between the two straight sections as the first chicane, we implement a special modeling tool, named EEHG optimizer. This tool has been successfully applied to maximize the prebunching with a reasonably low energy modulation, thereby generating intense coherent X-ray pulses within a short undulator length (a few meters) limited by the available space of a storage ring. Numerical simulations confirm that the optimized EEHG parameters can be directly applied to generate a 10 MW scale peak power with fully coherent ultrafast EUV to soft X-ray pulses based on the NSLS-II parameters. This method can be easily extended to other types of diffraction-limited storage rings.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser

It is known that X-ray free-electron lasers (FELs), which amplify light emitted by a relativistic electron beam, are extending nonlinear optical techniques to shorter wavelengths, adding element specificity by exciting and probing electronic transitions from core levels. These techniques would benefit tremendously from having a stable FEL source, generating spectrally pure and wavelength-tunable pulses. Here, we show that such requirements can be met by operating the FEL in the so-called echo-enabled harmonic generation (EEHG) configuration. Here, two external conventional lasers are used to precisely tailor the longitudinal phase space of the electron beam before emission of X-rays. We demonstrate high-gain EEHG lasing producing stable, intense, nearly fully coherent pulses at wavelengths as short as 5.9 nm (~211 eV) at the FERMI FEL user facility. Low sensitivity to electron-beam imperfections and observation of stable, narrow-band, coherent emission down to 2.6 nm (~474 eV) make the technique a prime candidate for generating laser-like pulses in the X-ray spectral region, opening the door to multidimensional coherent spectroscopies at short wavelengths.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Echo-Enabled Harmonic Generation Studies for the FERMI Free-Electron Laser

Studying ultrafast processes on the nanoscale with element specificity requires a powerful femtosecond source of tunable extreme-ultraviolet (XUV) or x-ray radiation, such as a free-electron laser (FEL). Current efforts in FEL development are aimed at improving the wavelength tunability and multicolor operation, which will potentially lead to the development of new characterization techniques offering a higher chemical sensitivity and improved spatial resolution. One of the most promising approaches is the echo-enabled harmonic generation (EEHG), where two external seed lasers are used to precisely control the spectro-temporal properties of the FEL pulse. Here, we study the expected performance of EEHG at the FERMI FEL, using numerical simulations. We show that, by employing the existing FERMI layout with minor modifications, the EEHG scheme will be able to produce gigawatt peak-power pulses at wavelengths as short as 5 nm. We discuss some possible detrimental effects that may affect the performance of EEHG and compare the results to the existing double-stage FEL cascade, currently in operation at FERMI. Finally, our simulations show that, after substantial machine upgrades, EEHG has the potential to deliver coherent multicolor pulses reaching wavelengths as short as 3 nm, enabling x-ray pump-x-ray probe experiments in the water window.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Comparing FEL Codes for Advanced Configurations

Various FEL codes employ different approximations and strategies to model the FEL radiation generation process. Many codes perform averaging procedures over various length scales in order to simplify the underlying dynamics. As FELs are developed in more advanced configurations beyond simple SASE, the assumptions of some codes may be called into question. Here, we compare the unaveraged code Puffin to averaged FEL codes including a new version of GENESIS in a variety of situations. In particular, we study a harmonic lasing setup, a High-Gain Harmonic Generation (HGHG) configuration modeled after the FERMI setup, and a potential Echo-Enabled Harmonic Generation (EEHG) configuration also at FERMI. Lastly, we find the codes are in good agreement, although small discrepancies do exist.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Toward a fully coherent tender and hard X-ray free-electron laser via cascaded EEHG in fourth-generation synchrotron light sources

Free-electron-laser-based beamlines utilize fully coherent laser pulses with extremely narrow bandwidth allowing direct use of X-rays without monochromators. This could be very beneficial for all users of current and future fourth-generation diffraction-limited synchrotron light sources (DL-SLSs) who need narrowband full-coherence high-brightness X-ray pulses. Based on our previous finding, i.e. that separating the two stages of echo-enabled harmonic generation (EEHG) with a few extra bending-magnet sections provides an effective way to increase the momentum compaction of chicane 1, one can simultaneously achieve adequate prebunching at extremely high harmonics as well as keep the energy modulation to the ideal minimum. This could open the door for cascaded EEHG, toward fully coherent tender and hard X-ray wavelengths. Built on our compact design of a twin-pulse seeding electron beam with an adjustable delay and timing jitter at the level of a few femtoseconds, a cascaded EEHG can be implemented, which includes two EEHG beamlines, where the radiation pulse generated by the first beamline with harmonic $h$ 1 could be used as the input seed laser pulse to the second beamline with harmonic $h$ 2 . Hence, the second radiator could potentially reach very high harmonics [$h$ = $h$ 1 (20)$h$ 2 (25–100)] from 500 to 2000, corresponding to tender and hard X-ray wavelengths. It is demonstrated that the cascaded EEHG scheme is compatible with almost any current or planned fourth-generation DL-SLS, with significant benefits for space-limited storage rings in particular. The main advantage is that this scheme requires almost no change of the storage-ring lattice and is fully compatible with other beamlines. Current proposals for rings with much longer straight sections would add self-amplified spontaneous emission as another viable option for storage-ring-based free-electron lasers.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Towards coherent X-ray free-electron lasers

Increased bandwidth and fluctuations are difficulties on the path towards generating intense fully coherent X-ray free-electron laser output. A recent experiment at FERMI Trieste observed that these problems can be overcome by an approach called echo-enabled harmonic generation.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Echo-enabled harmonics up to the 75th order from precisely tailored electron beams

The production of coherent radiation at ever shorter wavelengths has been a long-standing challenge since the invention of lasers1, 2 and the subsequent demonstration of frequency doubling3. Modern X-ray free-electron lasers (FELs) use relativistic electrons to produce intense X-ray pulses on few-femtosecond timescales4, 5, 6. However, the shot noise that seeds the amplification produces pulses with a noisy spectrum and limited temporal coherence. To produce stable transform-limited pulses, a seeding scheme called echo-enabled harmonic generation (EEHG) has been proposed7, 8, which harnesses the highly nonlinear phase mixing of the celebrated echo phenomenon9 to generate coherent harmonic density modulations in the electron beam with conventional lasers. Here, we report on a demonstration of EEHG up to the 75th harmonic, where 32 nm light is produced from a 2,400 nm laser. We also demonstrate that individual harmonic amplitudes are controlled by simple adjustment of the phase mixing. Results show the potential of laser-based manipulations to achieve precise control over the coherent spectrum in future X-ray FELs for new science10, 11.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Twin-pulse seeding enables pump-probe capabilities in the EUV to soft X-ray spectrum at synchrotron light sources

Having previously reported that separating the two stages of echo-enabled harmonic generation (EEHG) with one or more bending magnet (BM) sections allows the BMs to serve as the desired source of momentum compaction, here we demonstrate that this arrangement can greatly reduce the total energy modulation required by any 4th generation synchrotron light source, leading to higher repetition rates as well as stronger coherent radiation output power, with significant benefits. Since the EEHG beamline performance is mainly determined by the momentum compaction, beam emittances and beta functions of a storage ring lattice, allowing for different separations between the two stages is a straightforward way to increase the momentum compaction of chicane 1. This also enables pump-probe capabilities in a novel context, where twin-pulse seeding on the same electron bunch would allow two distinct radiation pulses with an adjustable delay in the range of 0.1 to 10 ps. In the twin-pulse seeding scheme, the same electron bunch could undergo modulation from two distinct laser pulses. Later stages would produce independent harmonics in subsequent straight sections. There are two variations of this twin-pulse seeding scheme, supporting different scientific applications. With a common modulation in stage 1, the first option allows simultaneously two independent radiation sources, with a full coverage of the EUV (2.5 to 50 nm) to soft X-ray (1.25 to 2.5 nm) spectrum; for the second option, the same stage 2 undulator could generate two coherent pulses both fitting within the FEL bandwidth, or at distinct harmonics. We present particle tracking simulation studies based on the APS-U lattice, including quantum excitation and radiation damping. These simulations indicate that there is no degradation of the modulated longitudinal phase space even when the two stages are separated by as many as 10 BM sections.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Minimum Spectral Bandwidth in Echo Seeded Free Electron Lasers

This paper examines the impact of non-linear longitudinal phase distortions on the spectral bandwidth in echo seeded free electron lasers (FELs). It extends the existing theory developed in Hemsing for echo-enabled harmonic generation (EEHG) to include finite laser pulse durations. An analytic expression for the shape of the optimized longitudinal bunching envelope is derived, and is used to determine the laser and electron beam pulse durations that minimize the seeded bandwidth in the presence of arbitrary phase distortions. The time-bandwidth product (TBP) is also derived, and is shown that the TBP and the bandwidth increase by no more than 2–√ from their transform-limited values when the bandwidth is minimized.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Minimum Spectral Bandwidth in Echo Seeded Free Electron Lasers

This paper examines the impact of non-linear longitudinal phase distortions on the spectral bandwidth in echo seeded free electron lasers (FELs). It extends the existing theory developed in Ref.~\cite{HemsingBunchingPhase} for echo-enabled harmonic generation (EEHG) to include finite laser pulse durations. An analytic expression for the shape of the optimized longitudinal bunching envelope is derived, and is used to determine the laser and electron beam pulse durations that minimize the seeded bandwidth in the presence of arbitrary phase distortions. The time-bandwidth product (TBP) is also derived, and is shown that the TBP and the bandwidth increase by no more than $\sqrt{2}$ from their transform-limited values when the bandwidth is minimized.

Hemsing, Erik↗