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Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser
Giovanni De Ninno, Primož Rebernik Ribič, 2019, izvirni znanstveni članek

Opis: 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.
Najdeno v: osebi
Ključne besede: free electron laser, coherence, x-rays
Objavljeno: 07.05.2019; Ogledov: 771; Prenosov: 0
.pdf Polno besedilo (6,89 MB)

Complete Characterization of Phase and Amplitude of Bichromatic Extreme Ultraviolet Light
Primož Rebernik Ribič, Giovanni De Ninno, 2019, izvirni znanstveni članek

Opis: Intense, mutually coherent beams of multiharmonic extreme ultraviolet light can now be created using seeded free-electron lasers, and the phase difference between harmonics can be tuned with attosecond accuracy. However, the absolute value of the phase is generally not determined. We present a method for determining precisely the absolute phase relationship of a fundamental wavelength and its second harmonic, as well as the amplitude ratio. Only a few easily calculated theoretical parameters are required in addition to the experimental data.
Najdeno v: osebi
Ključne besede: free-electron lasers, coherence, phase, attosecond
Objavljeno: 12.01.2020; Ogledov: 590; Prenosov: 0
.pdf Polno besedilo (293,60 KB)

A detailed investigation of single-photon laser enabled Auger decay in neon
Primož Rebernik Ribič, Giovanni De Ninno, 2019, izvirni znanstveni članek

Opis: Single-photon laser enabled Auger decay (spLEAD) is an electronic de-excitation process which was recently predicted and observed in Ne. We have investigated it using bichromatic phase-locked free electron laser radiation and extensive angle-resolved photoelectron measurements, supported by a detailed theoretical model. We first used separately the fundamental wavelength resonant with the Ne+ 2s–2p transition, 46.17 nm, and its second harmonic, 23.08 nm, then their phase-locked bichromatic combination. In the latter case the phase difference between the two wavelengths was scanned, and interference effects were observed, confirming that the spLEAD process was occurring. The detailed theoretical model we developed qualitatively predicts all observations: branching ratios between the final Auger states, their amplitudes of oscillation as a function of phase, the phase lag between the oscillations of different final states, and partial cancellation of the oscillations under certain conditions.
Najdeno v: osebi
Ključne besede: laser enabled Auger decay, free-electron lasers, neon
Objavljeno: 12.01.2020; Ogledov: 479; Prenosov: 0
.pdf Polno besedilo (996,35 KB)

Shortening the pulse duration in seeded free-electron lasers by chirped microbunching
Primož Rebernik Ribič, Takashi Tanaka, 2019, izvirni znanstveni članek

Opis: In externally seeded free-electron lasers (FELs) that rely on a frequency upconversion scheme to generate intense short-wavelength light pulses, the slippage effect in the radiator imposes a lower limit on the FEL pulse duration, which is typically on the order of a few tens of femtoseconds. Recently it was proposed that a combination of a chirped microbunch and a tapered undulator can be used to break this limit. Although the method has the potential to reduce the FEL pulse duration down to a level that cannot be achieved by current state-of-the-art technology, it requires a very short seed pulse (∼ one optical cycle or less), making it challenging to put this concept into practical use. Here, we propose an alternative technique to relax the requirement on the seed pulse length. We show that the modified scheme allows generation of FEL pulses with durations much shorter than that determined by the seed pulse and the slippage effect. The performance of the method, which can easily be implemented at existing seeded FEL user facilities, is evaluated through a campaign of analytical calculations and simulations. For our set of typical seeded FEL parameters, we expect the generation of 1.6 fs long pulses at 26 nm with a peak power of 10 GW using a 20 fs long chirped seed pulse operating at 260 nm.
Najdeno v: osebi
Ključne besede: free-electron lasers, short pulses, femtosecond
Objavljeno: 12.01.2020; Ogledov: 524; Prenosov: 0
.pdf Polno besedilo (1,21 MB)

Coherent THz Emission Enhanced by Coherent Synchrotron Radiation Wakefield
Primož Rebernik Ribič, Giovanni De Ninno, 2018, izvirni znanstveni članek

Opis: We demonstrate that emission of coherent transition radiation by a ∼1 GeV energy-electron beam passing through an Al foil is enhanced in intensity and extended in frequency spectral range, by the energy correlation established along the beam by coherent synchrotron radiation wakefield, in the presence of a proper electron optics in the beam delivery system. Analytical and numerical models, based on experimental electron beam parameters collected at the FERMI free electron laser (FEL), predict transition radiation with two intensity peaks at ∼0.3 THz and ∼1.5 THz, and extending up to 8.5 THz with intensity above 20 dB w.r.t. the main peak. Up to 80-µJ pulse energy integrated over the full bandwidth is expected at the source, and in agreement with experimental pulse energy measurements. By virtue of its implementation in an FEL beam dump line, this work promises dissemination of user-oriented multi-THz beamlines parasitic and self-synchronized to EUV and x-ray FELs.
Najdeno v: osebi
Ključne besede: terahertz radiation, free-electron lasers, coherent transition radiation
Objavljeno: 12.01.2020; Ogledov: 548; Prenosov: 0
.pdf Polno besedilo (1,62 MB)

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