185 research outputs found
Hollow Fiber Compression Technique: A Historical Perspective
This review analyzes the evolution, applications, and
future prospects of the hollow fiber compression technique, a pivotal
advancement in ultrafast laser technology. Over the past three
decades, this technique has emerged as a cornerstone, proving
instrumental in the generation of few-cycle pulses characterized
by millijoule-level energy, spanning a wide spectral range from ultraviolet
to mid-infrared wavelengths. Its versatility and efficiency
have found applications in diverse scientific disciplines, ranging
from attosecond science to extreme nonlinear optics. The review
delves into the historical development of the hollow fiber compression
technique, highlighting key milestones and technological
breakthroughs that have contributed to its current status. The
widespread adoption of this technique in laboratories on a global
scale is investigated, and an exploration is conducted into the
continuously reported innovative experimental implementations.
The impact of this technique on attosecond science is scrutinized,
emphasizing its role in the generation and application of isolated
attosecond pulses
Time-frequency mapping of two-colour photoemission driven by harmonic radiation
The use of few-femtosecond, extreme ultraviolet (XUV) pulses, produced by
high-order harmonic generation, in combination with few-femtosecond infrared
(IR) pulses in pump-probe experiments has great potential to disclose ultrafast
dynamics in molecules, nanostructures and solids. A crucial prerequisite is a
reliable characterization of the temporal properties of the XUV and IR pulses.
Several techniques have been developed. The majority of them applies phase
reconstruction algorithms to a photoelectron spectrogram obtained by ionizing
an atomic target in a pump-probe fashion. If the ionizing radiation is a single
harmonic, all the information is encoded in a two-color two-photon signal
called sideband (SB). In this work, we present a simplified model to interpret
the time-frequency mapping of the SB signal and we show that the temporal
dispersion of the pulses directly maps onto the shape of its spectrogram.
Finally, we derive an analytical solution, which allows us to propose a novel
procedure to estimate the second-order dispersion of the XUV and IR pulses in
real time and with no need for iterative algorithms
Mapping the spectral phase of isolated attosecond pulses by extreme-ultraviolet emission spectrum
An all-optical method is proposed for the measurement of the
spectral phase of isolated attosecond pulses. The technique is based on the
generation of extreme-ultraviolet (XUV) radiation in a gas by the
combination of an attosecond pulse and a strong infrared (IR) pulse with
controlled electric field. By using a full quantum simulation, we
demonstrate that, for particular temporal delays between the two pulses, the
IR field can drive back to the parent ions the photoelectrons generated by
the attosecond pulse, thus leading to the generation of XUV photons. It is
found that the generated XUV spectrum is notably sensitive to the chirp of
the attosecond pulse, which can then be reliably retrieved. A classical
quantum-path analysis is further used to quantitatively explain the main
features exhibited in the XUV emission
Novel beamline for attosecond transient reflection spectroscopy in a sequential two-foci geometry
We present an innovative beamline for extreme ultraviolet (XUV)-infrared (IR)
pump-probe reflection spectroscopy in solids with attosecond temporal
resolution. The setup uses an actively stabilized interferometer, where
attosecond pulse trains or isolated attosecond pulses are produced by
high-order harmonic generation in gases. After collinear recombination, the
attosecond XUV pulses and the femtosecond IR pulses are focused twice in
sequence by toroidal mirrors, giving two spatially separated interaction
regions. In the first region, the combination of a gas target with a
time-of-flight spectrometer allows for attosecond photoelectron spectroscopy
experiments. In the second focal region, an XUV reflectometer is used for
attosecond transient reflection spectroscopy (ATRS) experiments. Since the two
measurements can be performed simultaneously, precise pump-probe delay
calibration can be achieved, thus opening the possibility for a new class of
attosecond experiments on solids. Successful operation of the beamline is
demonstrated by the generation and characterization of isolated attosecond
pulses, the measurement of the absolute reflectivity of SiO2, and by performing
simultaneous photoemission/ATRS in Ge.Comment: 18 pages, 9 figure
Charge migration induced by attosecond pulses in bio-relevant molecules
After sudden ionization of a large molecule, the positive charge can migrate throughout the system on a sub-femtosecond time scale, purely guided by electronic coherences. The possibility to actively explore the role of the electron dynamics in the photo-chemistry of bio-relevant molecules is of fundamental interest for understanding, and perhaps ultimately controlling, the processes leading to damage, mutation and, more generally, to the alteration of the biological functions of the macromolecule. Attosecond laser sources can provide the extreme time resolution required to follow this ultrafast charge flow. In this review we will present recent advances in attosecond molecular science: after a brief description of the results obtained for small molecules, recent experimental and theoretical findings on charge migration in bio-relevant molecules will be discussed
A systematic study of the valence electronic structure of cyclo(Gly–Phe), cyclo(Trp–Tyr) and cyclo(Trp–Trp) dipeptides in the gas phase
The electronic energy levels of cyclo(glycine–phenylalanine), cyclo(tryptophan–tyrosine) and cyclo(tryptophan–tryptophan) dipeptides are investigated with a joint experimental and theoretical approach. Experimentally, valence photoelectron spectra in the gas phase are measured using VUV radiation. Theoretically, we first obtain low-energy conformers through an automated conformer–rotamer ensemble sampling scheme based on tight-binding simulations. Then, different first principles computational schemes are considered to simulate the spectra: Hartree–Fock (HF), density functional theory (DFT) within the B3LYP approximation, the quasi-particle GW correction, and the quantumchemistry CCSD method. Theory allows assignment of the main features of the spectra. A discussion on the role of electronic correlation is provided, by comparing computationally cheaper DFT scheme (and GW) results with the accurate CCSD method
Spatial aberrations in high-order harmonic generation
We investigate the spatial characteristics of high-order harmonic radiation
generated in argon, and observe cross-like patterns in the far field. An
analytical model describing harmonics from an astigmatic driving beam reveals
that these patterns result from the order and generation position dependent
divergence of harmonics. Even small amounts of driving field astigmatism may
result in cross-like patterns, coming from the superposition of individual
harmonics with spatial profiles elongated in different directions. By
correcting the aberrations using a deformable mirror, we show that fine-tuning
the driving wavefront is essential for optimal spatial quality of the
harmonics
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