293 results found
Barillot T, Alexander O, Cooper B, et al., 2021, Correlation-Driven Transient Hole Dynamics Resolved in Space and Time in the Isopropanol Molecule, PHYSICAL REVIEW X, Vol: 11, ISSN: 2160-3308
Driver T, Averbukh V, Frasiński LJ, et al., 2021, Two-dimensional partial covariance mass spectrometry for the top-down analysis of intact proteins., Analytical Chemistry, Vol: 93, Pages: 10779-10788, ISSN: 0003-2700
Two-dimensional partial covariance mass spectrometry (2D-PC-MS) exploits the inherent fluctuations of fragment ion abundances across a series of tandem mass spectra, to identify correlated pairs of fragment ions produced along the same fragmentation pathway of the same parent (e.g., peptide) ion. Here, we apply 2D-PC-MS to the analysis of intact protein ions in a standard linear ion trap mass analyzer, using the fact that the fragment-fragment correlation signals are much more specific to the biomolecular sequence than one-dimensional (1D) tandem mass spectrometry (MS/MS) signals at the same mass accuracy and resolution. We show that from the distribution of signals on a 2D-PC-MS map it is possible to extract the charge state of both parent and fragment ions without resolving the isotopic envelope. Furthermore, the 2D map of fragment-fragment correlations naturally separates the products of the primary decomposition pathways of the molecular ions from those of the secondary ones. We access this spectral information using an adapted version of the Hough transform. We demonstrate the successful identification of highly charged, intact protein molecules bypassing the need for high mass resolution. Using this technique, we also perform the in silico deconvolution of the overlapping fragment ion signals from two co-isolated and co-fragmented intact proteins, demonstrating a viable new method for the concurrent mass spectrometric identification of a mixture of intact protein ions from the same fragment ion spectrum.
Li S, Driver T, Al Haddad A, et al., 2021, Two-dimensional correlation analysis for x-ray photoelectron spectroscopy, Journal of Physics B: Atomic, Molecular and Optical Physics, Vol: 54, Pages: 1-9, ISSN: 0953-4075
X-ray photoelectron spectroscopy (XPS) measures the binding energy of core-level electrons, which are well-localised to specific atomic sites in a molecular system, providing valuable information on the local chemical environment. The technique relies on measuring the photoelectron spectrum upon x-ray photoionisation, and the resolution is often limited by the bandwidth of the ionising x-ray pulse. This is particularly problematic for time-resolved XPS, where the desired time resolution enforces a fundamental lower limit on the bandwidth of the x-ray source. In this work, we report a novel correlation analysis which exploits the correlation between the x-ray and photoelectron spectra to improve the resolution of XPS measurements. We show that with this correlation-based spectral-domain ghost imaging method we can achieve sub-bandwidth resolution in XPS measurements. This analysis method enables XPS for sources with large bandwidth or spectral jitter, previously considered unfeasible for XPS measurements.
Marangos J, Driver T, 2021, Correlation-driven transient hole dynamics resolved in space and time in the isopropanol molecule, Physical Review X, ISSN: 2160-3308
The possibility of suddenly ionized molecules undergoing extremely fast electron hole (or, hole)dynamics prior to significant structural change was first recognized more than 20 years ago andtermed charge migration. The accurate probing of ultrafast electron hole dynamics requires measurements that have both sufficient temporal resolution and can detect the localization of a specifichole within the molecule. We report an investigation of the dynamics of inner valence hole states inisopropanol where we use an x-ray pump/x-ray probe experiment, with site and state-specific probing of a transient hole state localized near the oxygen atom in the molecule, together with an abinitio theoretical treatment. We record the signature of transient hole dynamics and make the firsttentative observation of dynamics driven by frustrated Auger-Meitner transitions. We verify thatthe effective hole lifetime is consistent with our theoretical prediction. This state-specific measurement paves the way to widespread application for observations of transient hole dynamics localizedin space and time in molecules and thus to charge transfer phenomena that are fundamental inchemical and material physics.
Driver T, Bachhawat N, Frasinski L, et al., 2021, Chimera spectrum diagnostics for peptides using two-dimensional partial covariance mass spectrometry, Molecules, Vol: 26, ISSN: 1420-3049
The rate of successful identification of peptide sequences by tandem mass spectrometry (MS/MS) is adversely affected by the common occurrence of co-isolation and co-fragmentation of two or more isobaric or isomeric parent ions. This results in so-called `chimera spectra’, which feature peaks of the fragment ions from more than a single precursor ion. The totality of the fragment ion peaks in chimera spectra cannot be assigned to a single peptide sequence, which contradicts a fundamental assumption of the standard automated MS/MS spectra analysis tools, such as protein database search engines. This calls for a diagnostic method able to identify chimera spectra to single out the cases where this assumption is not valid. Here, we demonstrate that, within the recently developed two-dimensional partial covariance mass spectrometry (2D-PC-MS), it is possible to reliably identify chimera spectra directly from the two-dimensional fragment ion spectrum, irrespective of whether the co-isolated peptide ions are isobaric up to a finite mass accuracy or isomeric. We introduce ‘3-57 chimera tag’ technique for chimera spectrum diagnostics based on 2D-PC-MS and perform numerical simulations to examine its efficiency. We experimentally demonstrate the detection of a mixture of two isomeric parent ions, even under conditions when one isomeric peptide is at one five-hundredth of the molar concentration of the second isomer.
Li S, Driver T, Alexander O, et al., 2021, Time-resolved pump-probe spectroscopy with spectral domain ghost imaging, FARADAY DISCUSSIONS, Vol: 228, Pages: 488-501, ISSN: 1359-6640
Austin D, Johnson A, McGrath F, et al., 2021, Extracting sub-cycle electronic and nuclear dynamics from high harmonic spectra, Scientific Reports, Vol: 11, ISSN: 2045-2322
We present a new methodology for measuring few-femtosecond electronic and nuclear dynamics in both atoms and polyatomic molecules using multidimensional high harmonic generation (HHG) spectroscopy measurements, in which the spectra are recorded as a function of the laser intensity to form a two-dimensional data set. The method is applied to xenon atoms and to benzene molecules, the latter exhibiting significant fast nuclear dynamics following ionization. We uncover the signature of the sub-cycle evolution of the returning electron flux in strong-field ionized xenon atoms, implicit in the strong field approximation but not previously observed directly. We furthermore extract the nuclear autocorrelation function in strong field ionized benzene cations, which is determined to have a decay of τ0=4±1 fs, in good agreement with the τ0=3.5 fs obtained from direct dynamics variational multi-configuration Gaussian calculations. Our method requires minimal assumptions about the system, and is applicable even to un-aligned polyatomic molecules.
Driver T, Cooper B, Ayers R, et al., 2020, Two-dimensional partial covariance mass spectrometry of large molecules based on fragment correlations, Physical Review X, Vol: 10, Pages: 041004 – 1-041004 – 13, ISSN: 2160-3308
Covariance mapping [L. J. Frasinski, K. Codling, and P. A. Hatherly, Science 246, 1029 (1989)] is a well-established technique used for the study of mechanisms of laser-induced molecular ionization and decomposition. It measures statistical correlations between fluctuating signals of pairs of detected species (ions, fragments, electrons). A positive correlation identifies pairs of products originating from the same dissociation or ionization event. A major challenge for covariance-mapping spectroscopy is accessing decompositions of large polyatomic molecules, where true physical correlations are overwhelmed by spurious signals of no physical significance induced by fluctuations in experimental parameters. As a result, successful applications of covariance mapping have so far been restricted to low-mass systems, e.g., organic molecules of around 50 daltons (Da). Partial-covariance mapping was suggested to tackle the problem of spurious correlations by taking into account the independently measured fluctuations in the experimental conditions. However, its potential has never been realized for the decomposition of large molecules, because in these complex situations, determining and continuously monitoring multiple experimental parameters affecting all the measured signals simultaneously becomes unfeasible. We introduce, through deriving theoretically and confirming experimentally, a conceptually new type of partial-covariance mapping—self-correcting partial-covariance spectroscopy—based on a parameter extracted from the measured spectrum itself. We use the readily available total ion count as the self-correcting partial-covariance parameter, thus eliminating the challenge of determining experimental parameter fluctuations in covariance measurements of large complex systems. The introduced self-correcting partial covariance enables us to successfully resolve correlations of molecules as large as
O'Neal JT, Champenois EG, Oberli S, et al., 2020, Electronic Population Transfer via Impulsive Stimulated X-Ray Raman Scattering with Attosecond Soft-X-Ray Pulses, PHYSICAL REVIEW LETTERS, Vol: 125, ISSN: 0031-9007
Weaver B, Greening D, Tisch J, et al., 2020, Generation and measurement of isolated attosecond pulses with enhanced flux using a two colour synthesized laser field, Optics Express, Vol: 28, Pages: 23329-23337, ISSN: 1094-4087
We have generated isolated attosecond pulses and performed attosecond streaking measurements using a two-colour synthesized laser field consisting of a strong near-infrared few-cycle pulse and a weaker multi-cycle pulse centred at 400 nm. An actively stabilized interferometer was used to coherently combine the two pulses. Using attosecond streaking we characterised the electric fields of the two pulses and accurately retrieved the spectrum of the multi-cycle pulse. We demonstrated a two-fold increase in the flux of isolated attosecond pulses produced and show that their duration was minimally affected by the presence of the weaker field due to spectral filtering by a multilayer mirror.
Marangos JP, 2020, Accessing the quantum spatial and temporal scales with XFELs, Nature Reviews Physics, Vol: 2, Pages: 332-334, ISSN: 2522-5820
X-ray free-electron lasers (XFELs) are unique tools that are making possible time-resolved measurements of structural and electronic dynamics at the quantum spatial and temporal scales. Jonathan Marangos discusses the transformative scientific potential of this capability but also stresses the importance of lowering barriers to access to maximize scientific reach.
Johnson AS, Austin DR, Wood DA, et al., 2020, High-flux soft x-ray harmonic generation from ionization-shaped few-cycle laser pulses (vol 4, eaar3761, 2018), SCIENCE ADVANCES, Vol: 6, ISSN: 2375-2548
Longetti L, Randulova M, Ojeda J, et al., 2020, Photoemission from non-polar aromatic molecules in the gas and liquid phase, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 22, Pages: 3965-3974, ISSN: 1463-9076
Driver T, Li S, Champenois EG, et al., 2020, Attosecond transient absorption spooktroscopy: a ghost imaging approach to ultrafast absorption spectroscopy, Physical Chemistry Chemical Physics, Vol: 22, Pages: 2704-2712, ISSN: 1463-9076
The recent demonstration of isolated attosecond pulses from an X-ray free-electron laser (XFEL) opens the possibility for probing ultrafast electron dynamics at X-ray wavelengths. An established experimental method for probing ultrafast dynamics is X-ray transient absorption spectroscopy, where the X-ray absorption spectrum is measured by scanning the central photon energy and recording the resultant photoproducts. The spectral bandwidth inherent to attosecond pulses is wide compared to the resonant features typically probed, which generally precludes the application of this technique in the attosecond regime. In this paper we propose and demonstrate a new technique to conduct transient absorption spectroscopy with broad bandwidth attosecond pulses with the aid of ghost imaging, recovering sub-bandwidth resolution in photoproduct-based absorption measurements.
Duris J, Li S, Driver T, et al., 2020, Tunable isolated attosecond x-ray pulses with Gigawatt peak power from a free-electron laser, Nature Photonics, Vol: 14, Pages: 30-36, ISSN: 1749-4885
The quantum mechanical motion of electrons in molecules and solids occurs on the sub-femtosecond timescale. Consequently, the study of ultrafast electronic phenomena requires thegeneration of laser pulses shorter than 1 fs and of sufficient intensity to interact with their targetwith high probability. Probing these dynamics with atomic-site specificity requires the extensionof sub-femtosecond pulses to the soft X-ray spectral region. Here we report the generation of iso-lated soft X-ray attosecond pulses with an X-ray free-electron laser. Our source has a pulse energythat is a million times larger than any other source of isolated attosecond pulses in the soft X-rayspectral region, with a peak power exceeding 100 GW. This unique combination of high intensity,high photon energy and short pulse duration enables the investigation of electron dynamics withX-ray non-linear spectroscopy and single-particle imaging, unlocking a path towards a new era ofattosecond science.
Pettipher AJ, Weaver B, Greening D, et al., 2020, Optimisation of a Femtosecond Pulse Synthesiser for High Harmonic Generation Using the Semi-Classical Model, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-9020
Berrah N, Sanchez-Gonzalez A, Jurek Z, et al., 2019, Femtosecond-resolved observation of the fragmentation of buckminsterfullerene following X-ray multiphoton ionization (vol 15, pg 1279, 2019), NATURE PHYSICS, Vol: 15, Pages: 1301-1301, ISSN: 1745-2473
Berrah N, Sanchez-Gonzalez A, Jurek Z, et al., 2019, Femtosecond-resolved observation of the fragmentation of buckminsterfullerene following X-ray multiphoton ionization, Nature Physics, Vol: 15, Pages: 1279-1283, ISSN: 1745-2473
X-ray free-electron lasers have, over the past decade, opened up the possibility of understanding the ultrafast response of matter to intense X-ray pulses. In earlier research on atoms and small molecules, new aspects of this response were uncovered, such as rapid sequences of inner-shell photoionization and Auger ionization. Here, we studied a larger molecule, buckminsterfullerene (C60), exposed to 640 eV X-rays, and examined the role of chemical effects, such as chemical bonds and charge transfer, on the fragmentation following multiple ionization of the molecule. To provide time resolution, we performed femtosecond-resolved X-ray pump/X-ray probe measurements, which were accompanied by advanced simulations. The simulations and experiment reveal that despite substantial ionization induced by the ultrashort (20 fs) X-ray pump pulse, the fragmentation of C60 is considerably delayed. This work uncovers the persistence of the molecular structure of C60, which hinders fragmentation over a timescale of hundreds of femtoseconds. Furthermore, we demonstrate that a substantial fraction of the ejected fragments are neutral carbon atoms. These findings provide insights into X-ray free-electron laser-induced radiation damage in large molecules, including biomolecules.
Johnson AS, Avni T, Larsen E, et al., 2019, Attosecond soft X-ray high harmonic generation, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 377, ISSN: 1364-503X
Marangos JP, 2019, The measurement of ultrafast electronic and structural dynamics with X-rays, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 377, ISSN: 1364-503X
Drmota P, Marangos J, Greening D, et al., 2019, Investigation of valence band reconstruction methods for attosecond streaking data from surfaces, Optics Express, Vol: 27, Pages: 9394-9402, ISSN: 1094-4087
We analyze simulated streaked valence band photoemission with atomic streaking theory-based reconstruction methods to investigate the differences between atomic gas-phase streaking and valence band surface streaking. The careful distinction between atomic and surface streaking is a prerequisite to justify the application of atomic streaking theory-based reconstruction methods to surface streaking measurements. We show that neglecting the band structure underestimates the width of reconstructed photoelectron wavepackets, consistent with the Fourier transform limit of the band spectrum. We find that a fit of Gaussian wavepackets within the description of atomic streaking is adequate to a limited extent. Systematic errors that depend on the near-infrared skin depth, an inherently surface-specific property, are present in temporal widths of wavepackets reconstructed with atomic streaking theory-based methods.
Marangos J, 2019, Direct characterisation of tuneable few-femtosecond dispersive-wave pulses in the deep UV, Optics Letters, Vol: 44, Pages: 731-734, ISSN: 0146-9592
Dispersive wave emission (DWE) in gas-filled hollowcore dielectric waveguides is a promising source of tuneable coherent and broadband radiation, but so far the generation of few-femtosecond pulses usingthis technique has not been demonstrated. Using invacuum frequency-resolved optical gating, we directly characterise tuneable 3 fs pulses in the deep ultraviolet generated via DWE. Through numerical simulations, we identify that the use of a pressure gradient in the waveguide is critical for the generation of short pulses
Wyatt AS, Matía-Hernando P, Johnson AS, et al., 2019, Compression and amplification of SWIR single-cycle pulses for water window attosecond pulse generation
Schutte B, Peltz C, Austin DR, et al., 2018, Low-Energy Electron Emission in the Strong-Field Ionization of Rare Gas Clusters, PHYSICAL REVIEW LETTERS, Vol: 121, ISSN: 0031-9007
Johnson AS, Wood D, Austin DR, et al., 2018, Apparatus for soft x-ray table-top high harmonic generation, Review of Scientific Instruments, Vol: 89, ISSN: 0034-6748
There has been considerable recent interest in tabletop soft X-ray attosecond sources enabled by the new generation of intense, few-cycle laser sources at operating wavelengths longer than 800 nm. In our recent work [Johnson et al., Sci. Adv. 4(5), eaar3761 (2018)], we have demonstrated a new regime for the generation of X-ray attosecond pulses in the water window (284-540 eV) by high-harmonic generation, which resulted in soft X-ray fluxes of ≈109 photons/s and a maximum photon energy of 600 eV, an order of magnitude and 50 eV higher, respectively, than previously attained with few-cycle drivers. Here we present the key elements of our apparatus for the generation and detection of soft X-ray high harmonic radiation in the water window. Of critical importance is a differentially pumped gas target capable of supporting the multi-atmospheric pressures required to phase-match the high energy emission while strongly constraining the gas density, suppressing the effects of ionization and absorption outside the interaction region.
Johnson AS, Austin DR, Wood DA, et al., 2018, Correction for the Research Article: High-flux soft x-ray harmonic generation from ionization-shaped few-cycle laser pulses, Science Advances, Vol: 4, ISSN: 2375-2548
Laser-driven high-harmonic generation provides the only demonstrated route to generating stable, tabletop attosecondx-ray pulses but has low flux compared to other x-ray technologies. We show that high-harmonic generation can producehigher photon energies and flux by using higher laser intensities than are typical, strongly ionizing the medium andcreating plasma that reshapes the driving laser field. We obtain high harmonics capable of supporting attosecondpulses up to photon energies of 600 eV and a photon flux inside the water window (284 to 540 eV) 10 times higherthan previous attosecond sources. We demonstrate that operating in this regime is key for attosecond pulse generation in the x-ray range and will become increasingly important as harmonic generation moves to even longerwavelength driving fields.
Tisch JWG, Abdelrahman Z, Khokhlova M, et al., 2018, Chirp-control of resonant high-order harmonic generation in indium ablation plumes driven by intense few-cycle laser pulses, Optics Express, Vol: 26, Pages: 15745-15758, ISSN: 1094-4087
We have studied high-order harmonic generation (HHG) in an indium ablation plume driven by intense few-cycle laser pulses centered at 775 nm as a function of the frequency chirp of the laser pulse. We found experimentally that resonant emission lines between 19.7 eV and 22.3 eV (close to the 13th and 15th harmonic of the laser) exhibit a strong, asymmetric chirp dependence, with pronounced intensity modulations. The chirp dependence is reproduced by our numerical time-dependent Schrödinger equation simulations of a resonant HHG by the model indium ion. As demonstrated with our separate simulations of HHG within the strong field approximation, the resonance can be understood in terms of the chirp-dependent HHG photon energy coinciding with the energy of an autoionizing state to ground state transition with high oscillator strength. This supports the validity of the general theory of resonant four-step HHG in the few-cycle limit.
Johnson A, Austin D, Wood D, et al., 2018, High-flux soft x-ray harmonic generation from ionization-shaped few-cycle laser pulses, Science Advances, Vol: 4, ISSN: 2375-2548
Laser driven high harmonic generation provides the only demonstrated route to generatestable, tabletop attosecond X-ray pulses, but with low flux compared to other X-ray tech-nologies. Here we show that higher photon energies and flux can be obtained from highharmonic generation by using higher laser intensities than are typical, strongly ionizing themedium and creating plasma which reshapes the driving laser field. We obtain high harmon-ics capable of supporting attosecond pulses out to photon energies of 600 eV, and a photonflux inside the water window (284 eV to 540 eV) ten times higher than previous attosecondsources. We demonstrate that operating in this regime is key for attosecond pulse generationin the X-ray range, and will become increasingly important as harmonic generation movesto even longer wavelength driving fields.
Alharbi A, Boguslavskiy AE, Austin D, et al., 2018, Femtosecond Laser Mass Spectrometry and High Harmonic Spectroscopy of Xylene Isomers (vol 8, 3789, 2018), SCIENTIFIC REPORTS, Vol: 8, ISSN: 2045-2322
Matia-Hernando P, Witting T, Walke DJ, et al., 2018, Enhanced attosecond pulse generation in the vacuum ultraviolet using a two-colour driving field for high harmonic generation, Journal of Modern Optics, Vol: 65, Pages: 737-744, ISSN: 0950-0340
High-harmonic radiation in the extreme ultraviolet and soft X-ray spectral regions can be used to generate attosecond pulses and to obtain structural and dynamic information in atoms and molecules. However, these sources typically suffer from a limited photon flux. An additional issue at lower photon energies is the appearance of satellites in the time domain, stemming from insufficient temporal gating and the spectral filtering required for the isolation of attosecond pulses. Such satellites limit the temporal resolution. The use of multi-colour driving fields has been proven to enhance the harmonic yield and provide additional control, using the relative delays between the different spectral components for waveform shaping. We describe here a two-colour high-harmonic source that combines a few-cycle near-infrared pulse with a multi-cycle second harmonic pulse, with both relative phase and carrier-envelope phase stabilization. We observe strong modulations in the harmonic flux, and present simulations and experimental results supporting the suppression of satellites in sub-femtosecond pulses at 20 eV compared to the single colour field case, an important requirement for attosecond pump-probe measurements.
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