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. 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.
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The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.
The FEL code Genesis is available at http://genesis.web.psi.ch.
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McNeil, B. W. J. & Thompson, N. R. X-ray free-electron lasers. Nat. Photon. 4, 814–821 (2010).
Rebernik Ribic, P. & Margaritondo, G. Status and prospects of X-ray free-electron lasers (X-FELs): a simple presentation. J. Phys. Appl. Phys. 45, 213001 (2012).
Bonifacio, R., Pellegrini, C. & Narducci, L. M. Collective instabilities and high-gain regime in a free electron laser. Opt. Commun. 50, 373–378 (1984).
Ackermann, W. et al. Operation of a free-electron laser from the extreme ultraviolet to the water window. Nat. Photon. 1, 336–342 (2007).
Emma, P. et al. First lasing and operation of an angstrom-wavelength free-electron laser. Nat. Photon. 4, 641–647 (2010).
Ishikawa, T. et al. A compact X-ray free-electron laser emitting in the sub-ångström region. Nat. Photon. 6, 540–544 (2012).
Kang, H.-S. et al. Hard X-ray free-electron laser with femtosecond-scale timing jitter. Nat. Photon. 11, 708–713 (2017).
Amann, J. et al. Demonstration of self-seeding in a hard-X-ray free-electron laser. Nat. Photon. 6, 693–698 (2012).
Ratner, D. et al. Experimental demonstration of a soft X-Ray self-seeded free-electron laser. Phys. Rev. Lett. 114, 54801 (2015).
Lambert, G. et al. Injection of harmonics generated in gas in a free-electron laser providing intense and coherent extreme-ultraviolet light. Nat. Phys. 4, 296–300 (2008).
Togashi, T. et al. Extreme ultraviolet free electron laser seeded with high-order harmonic of Ti:Sapphire laser. Opt. Express 19, 317–324 (2011).
Ackermann, S. et al. Generation of coherent 19- and 38-nm radiation at a free-electron laser directly seeded at 38 nm. Phys. Rev. Lett. 111, 114801 (2013).
Yu, L. H. Generation of intense UV radiation by subharmonically seeded single-pass free-electron lasers. Phys. Rev. A 44, 5178–5193 (1991).
Yu, L.-H. et al. High-gain harmonic-generation free-electron laser. Science 289, 932–934 (2000).
Allaria, E. et al. Highly coherent and stable pulses from the FERMI seeded free-electron laser in the extreme ultraviolet. Nat. Photon. 6, 699–704 (2012).
Gauthier, D. et al. Spectrotemporal shaping of seeded free-electron laser pulses. Phys. Rev. Lett. 115, 114801 (2015).
De Ninno, G. et al. Single-shot spectro-temporal characterization of XUV pulses from a seeded free-electron laser. Nat. Commun. 6, 8075 (2015).
De Ninno, G., Mahieu, B., Allaria, E., Giannessi, L. & Spampinati, S. Chirped seeded free-electron lasers: self-standing light sources for two-color pump-probe experiments. Phys. Rev. Lett. 110, 64801 (2013).
Ferrari, E. et al. Widely tunable two-colour seeded free-electron laser source for resonant-pump resonant-probe magnetic scattering. Nat. Commun. 7, 10343 (2016).
Yu, L.-H. & Ben-Zvi, I. High-gain harmonic generation of soft X-rays with the ‘fresh bunch’ technique. Nucl. Instrum. Methods Phys. Res. A 393, 96–99 (1997).
Allaria, E. et al. Two-stage seeded soft-X-ray free-electron laser. Nat. Photon. 7, 913–918 (2013).
Stupakov, G. Using the beam-echo effect for generation of short-wavelength radiation. Phys. Rev. Lett. 102, 74801 (2009).
Xiang, D. & Stupakov, G. Echo-enabled harmonic generation free electron laser. Phys. Rev. Spec. Top. Accel. Beams 12, 30702 (2009).
Penn, G. Stable, coherent free-electron laser pulses using echo-enabled harmonic generation. Phys. Rev. Spec. Top. Accel. Beams 17, 110707 (2014).
Xiang, D. et al. Demonstration of the echo-enabled harmonic generation technique for short-wavelength seeded free electron lasers. Phys. Rev. Lett. 105, 114801 (2010).
Zhao, Z. T. et al. First lasing of an echo-enabled harmonic generation free-electron laser. Nat. Photon. 6, 360–363 (2012).
Xiang, D. et al. Evidence of high harmonics from echo-enabled harmonic generation for seeding X-ray free electron lasers. Phys. Rev. Lett. 108, 24802 (2012).
Hemsing, E. et al. Highly coherent vacuum ultraviolet radiation at the 15th harmonic with echo-enabled harmonic generation technique. Phys. Rev. Spec. Top. Accel. Beams 17, 70702 (2014).
Hemsing, E. et al. Echo-enabled harmonics up to the 75th order from precisely tailored electron beams. Nat. Photon. 10, 512–515 (2016).
Ratner, D., Fry, A., Stupakov, G. & White, W. Laser phase errors in seeded free electron lasers. Phys. Rev. Spec. Top. Accel. Beams 15, 30702 (2012).
Rebernik Ribič, P. et al. Echo-enabled harmonic generation studies for the FERMI free-electron laser. Photonics 4, 19 (2017).
Reiche, S. GENESIS 1.3: a fully 3D time-dependent FEL simulation code. Nucl. Instrum. Methods Phys. Res. A 429, 243–248 (1999).
Hemsing, E., Garcia, B., Huang, Z., Raubenheimer, T. & Xiang, D. Sensitivity of echo enabled harmonic generation to sinusoidal electron beam energy structure. Phys. Rev. Accel. Beams 20, 60702 (2017).
Saldin, E. L., Schneidmiller, E. A. & Yurkov, M. V. Klystron instability of a relativistic electron beam in a bunch compressor. Nucl. Instrum. Methods Phys. Res. A 490, 1–8 (2002).
Borland, M. Modeling of the microbunching instability. Phys. Rev. Spec. Top. Accel. Beams 11, 30701 (2008).
Spampinati, S. et al. Laser heater commissioning at an externally seeded free-electron laser. Phys. Rev. Spec. Top. Accel. Beams 17, 120705 (2014).
Schweigert, I. V. & Mukamel, S. Coherent ultrafast core-hole correlation spectroscopy: X-ray analogues of multidimensional NMR. Phys. Rev. Lett. 99, 163001 (2007).
Bencivenga, F. et al. Four-wave mixing experiments with extreme ultraviolet transient gratings. Nature 520, 205–208 (2015).
Prince, K. C. et al. Coherent control with a short-wavelength free-electron laser. Nat. Photon. 10, 176–179 (2016).
Lam, R. K. et al. Soft X-ray second harmonic generation as an interfacial probe. Phys. Rev. Lett. 120, 23901 (2018).
Tamasaku, K. et al. Nonlinear spectroscopy with X-ray two-photon absorption in metallic copper. Phys. Rev. Lett. 121, 83901 (2018).
Tanaka, S. & Mukamel, S. Coherent X-ray Raman spectroscopy: a nonlinear local probe for electronic excitations. Phys. Rev. Lett. 89, 43001 (2002).
Penco, G. et al. Experimental demonstration of electron longitudinal-phase-space linearization by shaping the photoinjector laser pulse. Phys. Rev. Lett. 112, 44801 (2014).
Penco, G. et al. Optimization of a high brightness photoinjector for a seeded FEL facility. J. Instrum. 8, P05015 (2013).
Di Mitri, S. et al. Design and simulation challenges for FERMI@elettra. Nucl. Instrum. Methods Phys. Res. A 608, 19–27 (2009).
Penco, G. et al. Time-sliced emittance and energy spread measurements at FERMI@elettra. In Proc. FEL2012 Nara, Japan (eds Tanaka, T. et al.) WEPD20, 417–420 (JACoW, 2013).
Craievich, P. et al. Implementation of radio-frequency deflecting devices for comprehensive high-energy electron beam diagnosis. IEEE Trans. Nucl. Sci. 62, 210–220 (2015).
Svetina, C. et al. PRESTO, the on-line photon energy spectrometer at FERMI: design, features and commissioning results. J. Synchrotron Radiat. 23, 35–42 (2016).
The authors thank G. Stupakov, S. Bettoni, D. Ratner, G. Marcus, F. Bencivenga, E. Pedersoli, M. Sacchi, C. Callegari, Z. Huang, T. Raubenheimer and A. Zholents for useful discussions. The authors also acknowledge the continuous support of R. Godnig, R. Bracco, R. Visintini, and the FERMI – Elettra operator group during the experiment. This work was supported in part by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract nos DE-AC02-76SF00515 and DE-AC02-05CH11231 and award no. 2017-SLAC-100382. D.G. was supported by an Outgoing CEA fellowship from the CEA-Enhanced Eurotalents programme, co-funded by FP7 Marie-Skłodowska-Curie COFUND programme (grant agreement 600382).
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