Harmonic-enhanced high-gain harmonic generation for a high repetition rate free-electron laser

Zhao, Shengzhi; Qin, Weilun; Huang, Senlin

doi:10.1017/hpl.2021.58

Cited by 3 publications

(8 citation statements)

References 38 publications

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“…Therefore, we can amplify the initial laser-induced energy modulation at the second, third, or higher harmonics toward short-wavelength seeded FELs. 33 The schematic layout of the self-modulation HGHG setup is shown in Fig. 2.…”

Section: Principlementioning

confidence: 99%

“…30 Moreover, the harmonic-enhanced HGHG numerically verifies that the 13.5-nm (20th harmonic) FEL radiation can be obtained by a UV seed laser. 33 To investigate the potential of the self-modulation scheme to generate ultrahigh harmonics, such as the 30th harmonic, the self-modulation HGHG is further discussed. With the parameters of the nominal case listed in Table 1, the optimization of the self-modulation scheme at SXFEL-UF toward shorter wavelengths is presented in Fig.…”

Section: Toward Short Wavelengthmentioning

confidence: 99%

“…30,31 Moreover, further studies have shown that the self-modulation method has a stability similar to HGHG and has the potential to achieve very high harmonics. 32,33 The utilization of an FEL oscillator as the seeding source for subsequent cascades has been proposed. [34][35][36][37] In addition, a resonator-like seed recirculation feedback system has been proposed to reuse the radiation in the modulator section to modulate the following electron bunches.…”

Section: Introductionmentioning

confidence: 99%

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High-repetition-rate seeded free-electron laser enhanced by self-modulation

2023

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The spectroscopic methods for the ultrafast electronic and structural dynamics of materials require fully coherent extreme ultraviolet and soft X-ray radiation with high-average brightness. Seeded free-electron lasers (FELs) are ideal sources for delivering fully coherent soft X-ray pulses. However, due to state-of-theart laser system limitations, it is challenging to meet the ultraviolet seed laser's requirements of sufficient energy modulation and high repetition rates simultaneously. The self-modulation scheme has been proposed and recently demonstrated in a seeded FEL to relax the seed laser requirements. Using numerical simulations, we show that the required seed laser intensity in the self-modulation is ~3 orders of magnitude lower than that in the standard high-gain harmonic generation (HGHG). The harmonic self-modulation can launch a singlestage HGHG FEL lasing at the 30th harmonic of the seed laser. Moreover, the proof-of-principle experimental results confirm that the harmonic self-modulation can still amplify the laser-induced energy modulation. These achievements reveal that the self-modulation can not only remarkably reduce the requirements of the seed laser but also improve the harmonic upconversion efficiency, which paves the way for realizing high-repetitionrate and fully coherent soft X-ray FELs.

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Section: Principlementioning

confidence: 99%

Section: Toward Short Wavelengthmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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High-repetition-rate seeded free-electron laser enhanced by self-modulation

2023

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“…The bunching factor of the fundamental and second harmonics increases by 28% and 68%, respectively, while the third harmonic increases by a factor of 1.7. Therefore, the induced relatively weak initial energy modulation can be further amplified in the second, third, or higher harmonics towards short-wavelength seeded FELs [39].…”

Section: Fig 1 Bunching Factor Versus Energy Modulation Amplitudementioning

confidence: 99%

“…Recently, the self-modulation of the electron beam has been experimentally demonstrated to be an effective method of reducing the requirement for an external seed laser [37,38]. Moreover, further studies have shown that the self-modulation method has similar stability to HGHG and has the potential to achieve very high harmonics [35,39]. More analysis of various methods to high-repetition-rate seeded FELs has been analyzed [40].…”

Section: Introductionmentioning

confidence: 99%

High-repetition-rate seeded free-electron laser enhanced by self-modulation

Yang¹,

Yan²,

Deng³

2022

Preprint

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Recently, the self-modulation scheme of a weakly pre-bunched electron beam has been proposed [Yan et al., Physical Review Letters 126, 084801 (2021)], which is of great promise for highrepetition-rate seeded free-electron lasers (FELs), such as high-gain harmonic generation (HGHG). In this paper, the self-modulation scheme is systematically analyzed and optimized, and further experiments in which the self-modulator is resonant at the second harmonic of the seed laser are conducted. The three-dimensional numerical simulations show that the required seed laser intensity in the self-modulation scheme is around three orders of magnitude lower than that of the standard HGHG through the optimization of the beam size or the peak current. More importantly, by reasonably setting the initial energy modulation and the resonance of the self-modulator, a more prominent bunching factor and lase at the 30th harmonic of the seed laser can be achieved in a single-stage HGHG. Moreover, the experiment results confirm that varying the resonance conditions of the self-modulator can still amplify the laser-induced energy modulation, where coherent radiation generated even at the 12th harmonic can be observed. These results indicate that the self-modulation scheme can remarkably reduce the requirements of the seed laser system while improving the harmonic up-conversion efficiency, which paves the way for realizing high-repetition-rate and fully coherent soft x-ray FELs.

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