We present an optical parametric chirped pulse amplification (OPCPA) system delivering 4.4 TW pulses centered at 810 nm with a sub-9 fs duration and a carrier-envelope phase stability of 350 mrad. ...The OPCPA setup pumped by sub-10 ps pulses from two Yb:YAG thin-disk lasers at 100 Hz repetition rate is optimized for a high conversion-efficiency. The terawatt pulses of the OPCPA are utilized for generating intense extreme ultraviolet (XUV) pulses by high-order harmonic generation, achieving XUV pulse energies approaching the microjoule level.
Carrier-envelope phase stable 4 fs near-IR pulses with 3 mJ energy were generated by spectral broadening of circularly polarized 8 mJ pulses in a differentially pumped 2 m long composite stretched ...flexible hollow fiber. The pulses were characterized using both second-harmonic generation frequency-resolved optical gating (SHG-FROG) and SHG d-scan methods.
We report on the direct experimental observation of pulse-splitting dynamics along a femtosecond filament. The fundamental pulse experiences a significant self-shortening during the propagation ...leading to pulse durations of 5.3 fs, corresponding to sub-3 cycles, which is measured without external pulse compression. A compression factor of eight could be achieved in a single filamentary stage. Theoretical modeling of the fundamental pulse propagation confirms our observed pulse structures and durations and gives further insight into the nonlinear dynamics during filamentation.
We use high-order harmonic spectroscopy to study ionization dynamics in a macroscopic target with tunable density, spanning over six orders of magnitude. In an
in situ
pump-probe experiment, the ...target is prepared at different densities with varying degrees of laser-induced ionization. High-order harmonic radiation is generated in the pre-ionized target, and a steepening in the decrease of the harmonic yield is observed for increasing pre-ionization, allowing not only to identify the contributing quantum paths during high-order harmonic generation but also in determining the amount of ionization within the target. The measurements allow probing of ionization dynamics in laser-induced plasma with high spatio-temporal resolution and are specifically of interest for the optimization of the harmonic generation process in high-density targets with number densities of up to 10
22
cm
−3
.
High-order harmonic spectroscopy allows one to extract information on fundamental quantum processes, such as the exit time in the tunneling of an electron through a barrier with attosecond time ...resolution and molecular structure with angstrom spatial resolution. Here, we study the spatial motion of the electron during high-order harmonic generation in an in situ pump-probe measurement using high-density liquid water droplets as a target. We show that molecules adjacent to the emitting electron-ion pair can disrupt the electron’s trajectory when positioned within the range of the maximum electronic excursion distance. This allows us to use the parent ion and the neighboring molecules as boundaries for the electronic motion to measure the maximum electronic excursion distance during the high-order harmonic generation process. Our analysis of the process is relevant for optimizing high-harmonic yields in dense media.
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We investigate two approaches for the spectral broadening and compression of 1-ps long pulses of a thin-disk laser amplifier running at 50 kHz repetition rate at 1030 nm wavelength. We find that with ...a single, 2.66-m long stretched flexible hollow fiber filled with xenon gas, Fourier transform limited output pulse duration of 66 fs can be directly reached. For larger pulse shortening, we applied a hybrid cascaded approach involving a BBO-based pre-compressor and a long hollow fiber. We could achieve 33-times temporal shortening of 1-ps pulses down to a duration of 30 fs at an overall efficiency of ~29% with an output power level of 3.7 W. These results demonstrate the potential of stretched flexible fibers with their free length scalability for shortening laser pulses of moderate peak power.
Recent measurements of time delays during tunnelling of cold atoms through an optically created potential barrier have fuelled an ongoing debate about possible time delays during light-induced ...tunnelling of an electron from an atom. Yet, such a delay—whether it is present or not—is only one quantity characterizing the tunnelling wavepacket, whilst the underlying dynamics are richer. Here we show how to complement photo-electron detection in laser-induced tunnelling by measuring the light emitted by the tunnelling electron—the so-called Brunel radiation. Using a combination of single- and two-colour driving fields, we identify the all-optical signatures of the reshaping of the tunnelling wavepacket as it emerges from the tunnelling barrier and moves away from the core. This reshaping includes not only an effective time delay but also the time-reversal asymmetry of the ionization process, which we describe theoretically and observe experimentally. We show how both delay and reshaping are mapped onto the polarization properties of the Brunel radiation, with different harmonics behaving as different hands of a clock moving at different speeds. The all-optical detection may also allow time-resolved measurements of optical tunnelling in condensed matter systems on the attosecond time scale.Whether or not an electron wavepacket accumulates a time delay when tunnelling out of an atom is still under debate. Improved all-optical characterization of the tunnelling dynamics by combining one- and two-colour driving fields may shed light on this question.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The ability to perform attosecond-pump attosecond-probe spectroscopy (APAPS) is a longstanding goal in ultrafast science. While first pioneering experiments demonstrated the feasibility of APAPS, the ...low repetition rates (10 to 120 Hz) and the large footprints of existing setups have so far hindered the widespread exploitation of APAPS. Here, we demonstrate two-color APAPS using a commercial laser system at 1 kHz, straightforward post-compression in a hollow-core fiber, and a compact high-harmonic generation (HHG) setup. The latter enables the generation of intense extreme-ultraviolet (XUV) pulses by using an out-of-focus HHG geometry and by exploiting a transient blueshift of the driving laser in the HHG medium. Near-isolated attosecond pulses are generated, as demonstrated by one-color and two-color XUV-pump XUV-probe experiments. Our concept allows selective pumping and probing on extremely short timescales in many laboratories and permits investigations of fundamental processes that are not accessible by other pump-probe techniques.
Purpose
This work aimed to compare the diagnostic performance of a metal artifact suppression sequence (MAVRIC-SL) for imaging of hip arthroplasties (HA) at 1.5 and 3 Tesla (T) field strength.
...Methods
Eighteen patients (10 females; aged 27–74) with HA were examined at 3.0 and 1.5 T within 3 weeks. The sequence protocol included 3D-MAVRIC-SL PD (coronal), 3D-MAVRIC-SL STIR (axial), FSE T1, FSE PD and STIR sequences. Anatomical structures and pathological findings were assessed independently by two radiologists. Artifact extent and technical quality (image quality, fat saturation and geometric distortion) were also evaluated. Findings at 1.5 and 3.0 T were compared using a Wilcoxon signed rank test.
Results
While image quality was better at 1.5 T, visualization of anatomic structures and clinical abnormalities was not significantly different using the two field strengths (
p
> 0.05). Fat suppression and amount of artifacts were significantly better at 1.5 T (
p
< 0.01). Inter- and intra-reader agreement for different anatomic details, image quality and visualization of abnormalities ranged from
k
= 0.62 to
k
= 1.00.
Conclusion
MAVRIC-SL at 1.5 T had a comparable diagnostic performance when compared MAVRIC-SL at 3.0 T; however, the higher field strength was associated with larger artifacts, limited image quality and worse fat saturation.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, VSZLJ, ZAGLJ
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