Time-Frequency Characterization of Femtosecond Extreme Ultraviolet Pulses (original) (raw)
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Direct spectrotemporal characterization of femtosecond extreme-ultraviolet pulses
Physical Review A, 2013
We propose a method for a straightforward characterization of the temporal shape of femtosecond pulses in the extreme-ultraviolet/soft X-ray spectral region. The approach is based on the presence of a significant linear frequency chirp in the pulse. This allows to establish an homothetic relation between the pulse spectrum and its temporal profile. The theoretical approach is reminiscent of the one employed by Fraunhofer for describing far-field diffraction. As an application, we consider the case of a seeded free-electron laser (FEL). Theory is successfully benchmarked with numerical simulations and with experimental data collected on the FERMI@Elettra FEL. The proposed method provides FEL users with an on-line, shot-to-shot spectro-temporal diagnostic for time-resolved experiments.
Applied Physics Letters, 2007
Two-color above threshold ionization of helium and xenon has been used to analyze the synchronization between individual pulses of the femtosecond extreme ultraviolet ͑XUV͒ free electron laser in Hamburg and an independent intense 120 fs mode-locked Ti:sapphire laser. Characteristic sidebands appear in the photoelectron spectra when the two pulses overlap spatially and temporally. The cross-correlation curve points to a 250 fs rms jitter between the two sources at the experiment. A more precise determination of the temporal fluctuation between the XUV and infrared pulses is obtained through the analysis of the single-shot sideband intensities.
Self-referenced characterization of femtosecond laser pulses by chirp scan
Optics Express, 2013
We investigate a variant of the d-scan technique, an intuitive pulse characterization method for retrieving the spectral phase of ultrashort laser pulses. In this variant a ramp of quadratic spectral phases is applied to the input pulses and the second harmonic spectra of the resulting pulses are measured for each chirp value. We demonstrate that a given field envelope produces a unique and unequivocal chirp-scan map and that, under some asymptotic assumptions, both the spectral amplitude and phase of the measured pulse can be retrieved analytically from only two measurements. An iterative algorithm can exploit the redundancy of the information contained in the chirp-scan map to discard experimental noise, artifacts, calibration errors and improve the reconstruction of both the spectral intensity and phase. This technique is compared to two reference characterization techniques (FROG and SRSI). Finally, we perform d-scan measurements with a simple grating-pair compressor.
Chirped pulse amplification in an extreme-ultraviolet free-electron laser
Nature communications, 2016
Chirped pulse amplification in optical lasers is a revolutionary technique, which allows the generation of extremely powerful femtosecond pulses in the infrared and visible spectral ranges. Such pulses are nowadays an indispensable tool for a myriad of applications, both in fundamental and applied research. In recent years, a strong need emerged for light sources producing ultra-short and intense laser-like X-ray pulses, to be used for experiments in a variety of disciplines, ranging from physics and chemistry to biology and material sciences. This demand was satisfied by the advent of short-wavelength free-electron lasers. However, for any given free-electron laser setup, a limit presently exists in the generation of ultra-short pulses carrying substantial energy. Here we present the experimental implementation of chirped pulse amplification on a seeded free-electron laser in the extreme-ultraviolet, paving the way to the generation of fully coherent sub-femtosecond gigawatt pulses...
Quantum theory of single subfemtosecond extreme-ultraviolet pulse measurements
Journal of the Optical Society of America B, 2003
Recently the initial measurements of single attosecond pulses with laser-dressed single-photon XUV ionization of gas atoms were reported. Determination of the extreme-ultraviolet (XUV) pulse duration from the electron spectrum is based on a classical theory. Although classical models are known to give a qualitatively correct description of strong laser-atom interaction, the validity range for accurate determination of subfemtosecond pulses must be scrutinized by quantum mechanical analysis. We establish a theoretical framework for the accurate temporal characterization of attosecond XUV pulses by using a Fourier-Bessel expansion of the XUV electron spectrum under the strong field approximation and a semiclassical derivation, setting earlier results on a rigorous theoretical footing. Our analysis reveals an improved scheme that is by more than an order of magnitude more efficient than the one used so far and allows for direct experimental discrimination between single and multiple attosecond pulses.
Physical Review A, 2005
We present a time-dependent analysis of high-order harmonics generated by a self-guided femtosecond laser pulse propagating through a long gas jet. A three-dimensional model is used to calculate the harmonic fields generated by laser pulses, which only differ by the sign of their initial chirp. The time-frequency distributions of the single-atom dipole and harmonic field reveal the dynamics of harmonic generation in the cutoff. A time-dependent phase-matching calculation was performed, taking into account the self-phase modulation of the laser field. Good phase matching holds for only few optical cycles, being dependent on the electron trajectory. When the cutoff trajectory is phase matched, emitted harmonics are locked in phase and the emission intensity is maximized.
Characterization of polarization shaped ultraviolet femtosecond laser pulses
2011
We present full vector-field characterization of amplitude, phase, and polarization controlled femtosecond laser pulses in the ultraviolet (UV) with a method termed DFG-XTURTLE. It combines the recently developed technique of tomographic ultrafast retrieval of transverse light E-fields (TURTLE) with the well-established cross-correlation frequency-resolved optical gating (XFROG) amplitude and phase retrieval algorithm. Three individual linear projections at 0°, 45°, and 90°of the vector-shaped field in the UV are frequency mixed with a well-characterized reference field at 800 nm and the generated frequency-resolved difference-frequency cross correlations in the visible are analyzed with a standard XFROG algorithm. The TURTLE search algorithm then establishes the full vector field of the UV pulses by finding the correct phase relationship between the 0°and 90°projections to reconstruct the projection at 45°. To retrieve the interpulse phase of temporally well-separated pulses, additional spectra must be taken. The handedness of shaped pulses can also be assigned with additional measurements.
Atoms
The generation of high-order harmonics in a semi-infinite cell by femtosecond laser pulses is a common practice for reliable coherent and low divergence XUV source beams for applications. Despite the relative simplicity of the experimental method, several phenomena coexist that affect the generated spectral and divergence characteristics of the high harmonic XUV frequency comb. The ionisation degree of the medium and the consequent plasma formation length imposes a spatiotemporal evolution of the fundamental EM field and XUV absorption. Varying the laser pulse chirp and the focusing conditions, as well as the gas density, we measured intense harmonic spectral and divergence variations attributed mainly to self-phase modulations of the laser EM field in the partially ionised medium. Additionally, low-divergence high harmonics are observed for certain laser chirp values attributed to the strong phase matching of only the short electron quantum path. Thus, a tunable, low divergent, and...
Phase-locked, time-delayed harmonic pulses for high spectral resolution in the extreme ultraviolet
Optics Letters, 2001
We present experiments in the time and frequency domains aimed at confirming the measured mutual phase coherence of time-delayed, collinear harmonic pulses. We show that pairs of phase-locked harmonic pulses of medium order can be generated for peak intensities up to ϳ1.5 10 14 W͞cm 2 in xenon, demonstrating the possibility of performing high-resolution spectroscopy in the extreme ultraviolet with Ramsey-like techniques.