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Generating high-energy few-cycle pulses is key in the study of light-matter interaction in the regime of high field physics. Attosecond science possess the necessary time resolution to study the underlying fundamental processes but requires repetitions rates on the order the kilohertz and stabilization of the Carrier-Envelope Phase. We present here a post-compression stage delivering 3.8fs pulses with 2.5mJ coupled to a Ti: Sa based 1 kHz TW-class laser which can deliver 17.8fs pulses with 350mrad shot to shot CEP noise. This is the first step towards high-energy few-cycle post-compression of the FAB laser at ATTOLAB-Orme.

The autoionization dynamics of the (2P1/2)ns/d Rydberg states in krypton are investigated using spatially isolated wave-mixing signals generated with a short train of subfemtosecond extreme ultraviolet (XUV) pulses and noncollinear, few-cycle near infrared pulses. Despite ubiquitous quantum beat oscillations from XUV-induced coherences within the excited-state manifold, these wave-mixing spectra allow for the simultaneous evaluation of autoionization lifetimes from a series of Rydberg states above the first ionization potential. Experimentally measured lifetimes of 22 ± 8 fs, 33 ± 6 fs, and 49 ± 6 fs for the wave-mixing signals emitting from the (2P1/2)6d/8s, (2P1/2)7d/9s, and (2P1/2)8d/10s resonances compare favorably with lifetimes for the (2P1/2)6d, 7d, and 8d Rydberg states determined from spectral linewidths. Analysis of the quantum beats reveals that the enhancement of wave-mixing pathways that couple the (2P1/2)nd states to themselves leads to individual reporter state-dependent decays in the wave-mixing signals. The results demonstrate the promise of wave-mixing spectroscopies with subfemtosecond XUV pulses to provide valuable insights into processes governed by electronic dynamics. [ABSTRACT FROM AUTHOR]

A combinationof ultrafast transient electronic absorption spectroscopy(TEAS) and transient vibrational absorption spectroscopy (TVAS) isused to investigate whether photoinduced N–H bond fission,mediated by a dissociative 1πσ* state, is activein aqueous adenine (Ade) at 266 and 220 nm. In order to isolate UV/visibleand IR spectral signatures of the adeninyl radical (Ade[-H]), formedas a result of N–H bond fission, TEAS and TVAS are performedon Ade in D2O under basic conditions (pD = 12.5), whichforms Ade[-H]−anions via deprotonation at the N7or N9 sites of Ade’s 7H and 9H tautomers. At 220 nm we observeone-photon detachment of an electron from Ade[-H]−, which generates solvated electrons (eaq–) together with Ade[-H] radicals,with clear signatures in both TEAS and TVAS. Additional wavelengthdependent TEAS measurements between 240–260 nm identify a thresholdof 4.9 ± 0.1 eV (∼250 nm) for this photodetachment processin D2O. Analogous TEAS experiments on aqueous Ade at pD= 7.4 generate a similar photoproduct signal together with eaq–afterexcitation at 266 and 220 nm. These eaq–are born from ionization ofAde, together with Ade+cations, which are indistinguishablefrom Ade[-H] radicals in TEAS. Ade+and Ade[-H] are foundto have different signatures in TVAS and we verify that the pD = 7.4photoproduct signal observed in TEAS following 220 nm excitation issolely due to Ade+cations. Based on these observations,we conclude that: (i) N–H bond fission in aqueous Ade is inactiveat wavelengths ≥220 nm; and (ii) if such a channel exists inaqueous solution, its threshold is strongly blue-shifted relativeto the onset of the same process in gas phase 9H-Ade (≤233nm). In addition, we extract excited state lifetimes and vibrationalcooling dynamics for 9H-Ade and Ade[-H]−. In both cases, excited state lifetimes of <500fs are identified, while vibrational cooling occurs within a timeframe of 4–5 ps. In contrast, 7H-Ade is confirmed to have alonger excited state lifetime of ∼5–10 ps through bothTEAS and TVAS. [ABSTRACT FROM AUTHOR]

The autoionization dynamics of the ( 2 P 1/2 )ns/d Rydberg states in krypton are investigated using spatially isolated wave-mixing signals generated with a short train of subfemtosecond extreme ultraviolet (XUV) pulses and noncollinear, few-cycle near infrared pulses. Despite ubiquitous quantum beat oscillations from XUV-induced coherences within the excited-state manifold, these wave-mixing spectra allow for the simultaneous evaluation of autoionization lifetimes from a series of Rydberg states above the first ionization potential. Experimentally measured lifetimes of 22 ± 8 fs, 33 ± 6 fs, and 49 ± 6 fs for the wave-mixing signals emitting from the ( 2 P 1/2 )6d/8s, ( 2 P 1/2 )7d/9s, and ( 2 P 1/2 )8d/10s resonances compare favorably with lifetimes for the ( 2 P 1/2 )6d, 7d, and 8d Rydberg states determined from spectral linewidths. Analysis of the quantum beats reveals that the enhancement of wave-mixing pathways that couple the ( 2 P 1/2 )nd states to themselves leads to individual reporter state-dependent decays in the wave-mixing signals. The results demonstrate the promise of wave-mixing spectroscopies with subfemtosecond XUV pulses to provide valuable insights into processes governed by electronic dynamics.

Attosecond science opened the door to observing nuclear and electronic dynamics in real time and has begun to expand beyond its traditional grounds. Among several spectroscopic techniques, X-ray transient absorption spectroscopy has become key in understanding matter on ultrafast time scales. In this review, we illustrate the capabilities of this unique tool through a number of iconic experiments. We outline how coherent broadband X-ray radiation, emitted in high-harmonic generation, can be used to follow dynamics in increasingly complex systems. Experiments performed in both molecules and solids are discussed at length, on time scales ranging from attoseconds to picoseconds, and in perturbative or strong-field excitation regimes. This article is part of the theme issue 'Measurement of ultrafast electronic and structural dynamics with X-rays'.

Ultrafast deactivation pathways bestow photostability on nucleobases and hence preserve the structural integrity of DNA following absorption of ultraviolet (UV) radiation. One controversial recovery mechanism proposed to account for this photostability involves electron-driven proton transfer (EDPT) in Watson-Crick base pairs. The first direct observation is reported of the EDPT process after UV excitation of individual guanine-cytosine (G⋅C) Watson-Crick base pairs by ultrafast time-resolved UV/visible and mid-infrared spectroscopy. The formation of an intermediate biradical species (G[-H]⋅C[+H]) with a lifetime of 2.9 ps was tracked. The majority of these biradicals return to the original G⋅C Watson-Crick pairs, but up to 10% of the initially excited molecules instead form a stable photoproduct G*⋅C* that has undergone double hydrogen-atom transfer. The observation of these sequential EDPT mechanisms across intermolecular hydrogen bonds confirms an important and long debated pathway for the deactivation of photoexcited base pairs, with possible implications for the UV photochemistry of DNA., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)