Abstract: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… Show more
“…Seeding coherent EUV to soft X-ray emission can be accomplished using a compact EEHG design via two SSs of a SR 1 , 2 . This design utilizes the BM section between these two SSs as the first chicane.…”
Section: Resultsmentioning
confidence: 99%
“…Even in a short radiator case (a few meters), the final CR power is negatively correlated to the final energy modulation of the beam slice. Thus, higher final energy spread for the part of the beam that interacts with the external laser leads to lower peak power 2 , 20 , 21 . Figure 3 The normalized final energy spread as a function of the momentum compaction of stage 1 is shown for harmonic 50 (red), 100 (black), 150 (blue), and 200 (green), respectively.…”
Section: Resultsmentioning
confidence: 99%
“…Compared to linac sources, the 4th generation SLSs have several key constraints: (1) long bunch length (at least a few picoseconds); (2) large energy spread; (3) low peak current. Because of these limitations, some form of external seeding via a laser system is required to generate shorter radiation pulses 1 , 2 . When conventional high-gain harmonic generation (HGHG) 3 – 6 is utilized, a great deal of seed laser power is required to generate coherent radiation (CR) at wavelengths significantly below what a conventional laser technology can deliver due to the large energy spread.…”
Section: Introductionmentioning
confidence: 99%
“…The initial stage requires a significant momentum compaction; however, it can be set to a specific value still having a reasonable range of tunability. Especially, this scheme is well suited to SR-based FELs, as we have shown that the two stages of EEHG can be placed in two straight sections (SSs) separated by one or more bending magnet (BM) sections, which provide the required momentum compaction 1 , 2 . Thus, EEHG produces short CR pulses 8 – 16 at high repetition rates, is fully compatible with SLSs (no need of any lattice change), as well as allows the accessibility to much higher harmonics toward the soft X-ray spectrum.…”
Section: Introductionmentioning
confidence: 99%
“…Building on our recent development of utilizing two straight sections (SSs) of a SR to seed coherent emission in the EUV to soft X-ray range 1 , 2 , we present a modified EEHG, twin-pulse seeding, where multiple laser pulses are used for the first stage of seeding within a single modulator to generate distinct regions of modulation, and the final stage of seeding for each region can be performed in a different SS to allow a broad range of independent tunability. Twin-pulse seeding is fully compatible with the large energy spread of a SR as well as the small momentum compaction per BM section intrinsically associated with a 4th generation SLS, as the desired momentum compaction can be accumulated over multiple BM sections.…”
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.
“…Seeding coherent EUV to soft X-ray emission can be accomplished using a compact EEHG design via two SSs of a SR 1 , 2 . This design utilizes the BM section between these two SSs as the first chicane.…”
Section: Resultsmentioning
confidence: 99%
“…Even in a short radiator case (a few meters), the final CR power is negatively correlated to the final energy modulation of the beam slice. Thus, higher final energy spread for the part of the beam that interacts with the external laser leads to lower peak power 2 , 20 , 21 . Figure 3 The normalized final energy spread as a function of the momentum compaction of stage 1 is shown for harmonic 50 (red), 100 (black), 150 (blue), and 200 (green), respectively.…”
Section: Resultsmentioning
confidence: 99%
“…Compared to linac sources, the 4th generation SLSs have several key constraints: (1) long bunch length (at least a few picoseconds); (2) large energy spread; (3) low peak current. Because of these limitations, some form of external seeding via a laser system is required to generate shorter radiation pulses 1 , 2 . When conventional high-gain harmonic generation (HGHG) 3 – 6 is utilized, a great deal of seed laser power is required to generate coherent radiation (CR) at wavelengths significantly below what a conventional laser technology can deliver due to the large energy spread.…”
Section: Introductionmentioning
confidence: 99%
“…The initial stage requires a significant momentum compaction; however, it can be set to a specific value still having a reasonable range of tunability. Especially, this scheme is well suited to SR-based FELs, as we have shown that the two stages of EEHG can be placed in two straight sections (SSs) separated by one or more bending magnet (BM) sections, which provide the required momentum compaction 1 , 2 . Thus, EEHG produces short CR pulses 8 – 16 at high repetition rates, is fully compatible with SLSs (no need of any lattice change), as well as allows the accessibility to much higher harmonics toward the soft X-ray spectrum.…”
Section: Introductionmentioning
confidence: 99%
“…Building on our recent development of utilizing two straight sections (SSs) of a SR to seed coherent emission in the EUV to soft X-ray range 1 , 2 , we present a modified EEHG, twin-pulse seeding, where multiple laser pulses are used for the first stage of seeding within a single modulator to generate distinct regions of modulation, and the final stage of seeding for each region can be performed in a different SS to allow a broad range of independent tunability. Twin-pulse seeding is fully compatible with the large energy spread of a SR as well as the small momentum compaction per BM section intrinsically associated with a 4th generation SLS, as the desired momentum compaction can be accumulated over multiple BM sections.…”
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.
Coherent terahertz (THz) radiation sources based on a storage ring hold a significant future for generating high average power terahertz radiation, as the electron beam possesses a high revolution frequency. We propose a novel scheme to generate a high repetition rate coherent THz radiation leveraging the energy modulation self-amplification technology. In this scheme, utilizing the interaction of external intensity-modulated laser pulses with the electron beam can lead to a customized manipulation of the electron beam, such as a periodic longitudinal density modulation with a submillimeter scale for coherent THz radiation. Positively, it can propel the repetition rate when the peak power requirement of an external laser system is decreased. Thus, we employ a self-modulation method to enhance the initial weak energy modulation induced by the laser directly. In the meanwhile, the use of self-modulation can bypass the limitation that the bandwidth of a long modulator should be smaller than that of the external wideband laser source, which is necessary to shape the intensity envelope flexibly. The one-dimensional analytical description of electron longitudinal dynamic during the self-modulation process is given, which confirms the effective enhancement of the modulation at THz band. Three-dimensional time-dependent simulation results based on the parameters of Hefei light source-II show that the coherent THz radiation pulses with a repetition rate of 10 kHz can be generated.
Published by the American Physical Society
2024
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.
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