156 results found
Debrah DA, Stewart GA, Basnayake G, et al., 2019, Direct in-situ single-shot measurements of the absolute carrier-envelope phases of ultrashort pulses, Optics Letters, Vol: 44, Pages: 3582-3585, ISSN: 0146-9592
Many important physical processes such as nonlinear optics and coherent control are highly sensitive to the absolute carrier-envelope phase (CEP) of driving ultrashort laser pulses. This makes the measurement of CEP immensely important in relevant fields. Even though relative CEPs can be measured with a few existing technologies, the estimate of the absolute CEP is not straightforward and always requires theoretical inputs. Here, we demonstrate a novel in-situ technique based on angular streaking that can achieve such a goal without complicated calibration procedures. Single-shot measurements of the absolute CEP have been achieved with an estimated precision of 0.19 radians.
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
Mecseki K, Hoeppner H, Buescher M, et al., 2018, Hard X-ray induced fast secondary electron cascading processes in solids, APPLIED PHYSICS LETTERS, Vol: 113, ISSN: 0003-6951
Recent studies confirmed that the materials used in the extreme UV and soft X-ray regime for precise characterization of intense free-electron laser pulses (e.g., Si3N4) do not work efficiently in the hard X-ray regime, which is due to the fact that the impact of a hard X-ray photon is followed by a series of electron cascading processes. Following theoretical indication, we show that this limitation can be circumvented and the cascading time can be significantly reduced if the X-ray photon energy is double the ionization energy. We investigate an alternative material for pulse diagnostics, SnO2, using the Linac Coherent Light Source at photon energies of 5 keV and 9 keV. We prove the validity of the concept and show that it has a large potential for practical applications. By applying the proposed criteria, the temporal accuracy of the non-invasive pulse diagnostic tools can be improved in current and emerging hard X-ray facilities.
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.
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.
Wyatt AS, Matía-Hernando P, Johnson AS, et al., 2018, Compression, amplification and characterization of few-cycle shortwavelength infrared pulses, ISSN: 0277-786X
© 2018 SPIE. We present a Ti:Sapphire pumped optical parametric amplifier for the simultaneous amplification and compression of sub-10fs ultrashort pulses centered at 1.7um; third-harmonic generation dispersion scan in bulk glass is used for temporal pulse characterization.
Witting T, Greening G, Walke D, et al., 2017, Spatio-temporal characterization of optical waveforms, Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Pulse characterization technology to characterize space-time couplings exists but most technqiues are not suiatable for few-cycle pulses. A lot of recent work has been focussed on combining modern few-cycle pulse characterization methods with spatial phase measurements based on a filtered reference pulse.This work reviews current state of the art in this field and also show recent results and progress in the self-referenced characterization of near single cycle pulses with space-time couplings. Using SEA-F-SPIDER the spatio-temporal electric field of a laser pulse can be reconstructed without the need for a reference pulse. In the current implementation we can recover the field E(x,t) in one spatial dimension. Measurements of ultrafast wavefront rotation and pulse front tilt in pulses generated in hollow fiber compressors are presented. The paper also discusses application in OPCPA and NOPA systems where the amplified pulses are expected to carry a significant amount of space-time couplings. Furthermore, avenues towards the extension of the technique to both spatial dimensions for a complete reconstruction of E(x,y,t) are discussed.
Witting T, Greening D, Walke D, et al., 2017, Near single-cycle pulse characterization with time-domain ptychography, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-9020
Barillot TR, Matia-Hernando P, Greening D, et al., 2017, Towards XUV pump-probe experiments in the femtosecond to sub-femtosecond regime: New measurement of the helium two-photon ionization cross-section, Chemical Physics Letters, Vol: 683, Pages: 38-42, ISSN: 0009-2614
Non-linear photoionization of molecules in the 10–50 eV range is a prerequisite for pump-probe measurements with sub-femtosecond resolution, but hitherto has been limited to femtosecond resolution, low repetition rate and high photon flux laser systems. We demonstrate two-photon single ionization of helium atoms using 100 pJ, 1.34 fs pulses (main peak FWHM = 680 as) at 1 kHz repetition rate with a central photon energy of 19.6 eV. We obtained an exponent of 2:27 0:21 for the intensity dependence of the signal and a two-photon ionization cross-section of 5:0 0:5 x 10−50 cm4 s. Our work opens the possibility of attosecond pump-probe measurements of ultrafast molecular processes.
Mercer IP, Witting T, Driver T, et al., 2017, Angle-resolved coherent wave mixing using a 4 fs ultra-broad bandwidth laser, Optics Letters, Vol: 42, Pages: 859-862, ISSN: 0146-9592
We demonstrate angle-resolved coherent (ARC) wave mixing using 4 fs light pulses derived from a laser source that spans 550–1000 nm. We believe this to be the shortest pulse duration used to date in coherent multi-dimensional spectroscopy. The marriage of this ultra-broad band, few-cycle coherent source with the ARC technique will permit new investigations of the interplay between energy transfers and quantum superposition states spanning 8200 cm−1. We applied this configuration to measurements on the photosynthetic low light (LL) complex from Rhodopseudomonas palustris in solution at ambient temperature. We observe bi-exponential population dynamics for energy transfer across 5500 cm−1 (0.65 eV), which we attribute to energy transfer from the transition of bacteriochlorophylls to the B850 pigment of the complex. We believe for the first time, to the best of our knowledge, we demonstrate that ARC maps can be recorded using a single laser pulse.
Schuette B, Ye P, Patchkovskii S, et al., 2016, Strong-field ionization of clusters using two-cycle pulses at 1.8 μm, Scientific Reports, Vol: 6, ISSN: 2045-2322
The interaction of intense laser pulses with nanoscale particles leads to the production of high-energy electrons, ions, neutral atoms, neutrons and photons. Up to now, investigations have focused on near-infrared to X-ray laser pulses consisting of many optical cycles. Here we study strong-field ionization of rare-gas clusters (103 to 105 atoms) using two-cycle 1.8 μm laser pulses to access a new interaction regime in the limit where the electron dynamics are dominated by the laser field and the cluster atoms do not have time to move significantly. The emission of fast electrons with kinetic energies exceeding 3 keV is observed using laser pulses with a wavelength of 1.8 μm and an intensity of 1 × 1015 W/cm2, whereas only electrons below 500 eV are observed at 800 nm using a similar intensity and pulse duration. Fast electrons are preferentially emitted along the laser polarization direction, showing that they are driven out from the cluster by the laser field. In addition to direct electron emission, an electron rescattering plateau is observed. Scaling to even longer wavelengths is expected to result in a highly directional current of energetic electrons on a few-femtosecond timescale.
Austin DR, witting T, sebastien J, et al., 2016, Spatio-temporal characterization of intense few-cycle 2 μm pulses, Optics Express, Vol: 24, Pages: 24786-24798, ISSN: 1094-4087
We present a variant of spatially encoded spectral shearing interferometry for measuring two-dimensional spatio-temporal slices of few-cycle pulses centered around 2μm. We demonstrate experimentally that the device accurately retrieves the pulse-front tilt caused by angular dispersion of two-cycle pulses. We then use the technique to characterize 500–650 μJ pulses from a hollow fiber pulse compressor, with durations as short as 7.1 fs (1.3 optical cycles).
Witting T, Greening D, Walke D, et al., 2016, Time-domain ptychography of over-octave-spanning laser pulses in the single-cycle regime., Optics Letters, Vol: 41, Pages: 4218-4221, ISSN: 1539-4794
We report, to the best of our knowledge, the first application of time-domain ptychography for the characterization of few-cycle laser pulses. Our method enables zero-additional phase measurements of over-octave-spanning laser pulses in the single cycle regime. The spectral phase is recovered using a robust ptychography algorithm that requires no input apart from the measured data trace. In addition to numerical tests, we validate our new device experimentally by reconstructing the complex electric field of a 1.5 cycle laser pulse with a bandwidth spanning 490 to 1060 nm. We further check the accuracy of our device by comparing the measured phases of octave-spanning chirped pulses to the known dispersion of fused silica glass.
Witting T, Austin DR, Barillot T, et al., 2016, Self-referenced characterization of space-time couplings in near-single-cycle laser pulses, Optics Letters, Vol: 41, Pages: 2382-2385, ISSN: 1539-4794
We report on the characterization of space–time couplingsin high-energy sub-2-cycle 770 nm laser pulses using a selfreferencingsingle-frame method. Using spatially encodedarrangement filter-based spectral phase interferometry fordirect electric field reconstruction, we characterize fewcyclepulses with a wavefront rotation of 2.8 × 1011 rev∕s(1.38 mrad per half-cycle) and pulses with pulse fronttilts ranging from −0.33 fs∕μm to −3.03 fs∕μm in thefocus.
Wyatt AS, Witting T, Schiavi A, et al., 2016, Attosecond sampling of arbitrary optical waveforms, Optica, Vol: 3, Pages: 303-310, ISSN: 2334-2536
Advances in the generation of ultrashort laser pulses, and the emergence of new research areas such as attosecond science, nanoplasmonics, coherent control, and multidimensional spectroscopy, have led to the need for a new class of ultrafast metrology that can measure the electric field of complex optical waveforms spanning the ultraviolet to the infrared. Important examples of such waveforms are those produced by spectral control of ultrabroad bandwidth pulses, or by Fourier synthesis. These are typically tailored for specific purposes, such as to increase the photon energy and flux of high-harmonic radiation, or to control dynamical processes by steering electron dynamics on subcycle time scales. These applications demand a knowledge of the full temporal evolution of the field. Conventional pulse measurement techniques that provide estimates of the relative temporal or spectral phase are unsuited to measure such waveforms. Here we experimentally demonstrate a new, all-optical method for directly measuring the electric field of arbitrary ultrafast optical waveforms. Our method is based on high-harmonic generation (HHG) driven by a field that is the collinear superposition of the waveform to be measured with a stronger probe laser pulse. As the delay between the pulses is varied, we show that the field of the unknown waveform is mapped to energy shifts in the high-harmonic spectrum, allowing a direct, accurate, and rapid retrieval of the electric field with subcycle temporal resolution at the location of the HHG.
Austin DR, Witting T, Ye P, et al., 2016, Temporal Characterization of Two Octave Hollow Fiber Supercontinuum
© OSA 2016. We measure the temporal profile of a 600 μJ hollow fiber supercontinuum spanning 640-2600 nm. At the fiber output, we observe extreme self-steepening and self-compression. The pulse is suitable for multi-channel compression to the sub-cycle regime.
Fabris D, Holgado W, Silva F, et al., 2015, Single-shot implementation of dispersion-scan for the characterization of ultrashort laser pulses, OPTICS EXPRESS, Vol: 23, Pages: 32803-32808, ISSN: 1094-4087
Fabris D, Witting T, Okell WA, et al., 2015, Synchronized pulses generated at 20 eV and 90 eV for attosecond pump-probe experiments, Nature Photonics, Vol: 9, Pages: 383-387, ISSN: 1749-4885
Okell WA, Witting T, Fabris D, et al., 2015, Temporal broadening of attosecond photoelectron wavepackets from solid surfaces, Optica, Vol: 2, Pages: 383-387, ISSN: 2334-2536
Haessler S, Balciunas T, Fan G, et al., 2015, Optimization of Quantum Trajectories Driven by Strong-Field Waveforms, 19th International Conference on Ultrafast Phenomena, Publisher: SPRINGER-VERLAG BERLIN, Pages: 72-77, ISSN: 0930-8989
Arrell CA, Ojeda J, Sabbar M, et al., 2014, A simple electron time-of-flight spectrometer for ultrafast vacuum ultraviolet photoelectron spectroscopy of liquid solutions, Review of Scientific Instruments, Vol: 85, ISSN: 1089-7623
We present a simple electron time of flight spectrometer for time resolved photoelectron spectroscopy of liquid samples using a vacuum ultraviolet (VUV) source produced by high-harmonic generation. The field free spectrometer coupled with the time-preserving monochromator for the VUV at the Artemis facility of the Rutherford Appleton Laboratory achieves an energy resolution of 0.65 eV at 40 eV with a sub 100 fs temporal resolution. A key feature of the design is a differentially pumped drift tube allowing a microliquid jet to be aligned and started at ambient atmosphere while preserving a pressure of 10−1 mbar at the micro channel plate detector. The pumping requirements for photoelectron (PE) spectroscopy in vacuum are presented, while the instrument performance is demonstrated with PE spectra of salt solutions in water. The capability of the instrument for time resolved measurements is demonstrated by observing the ultrafast (50 fs) vibrational excitation of water leading to temporary proton transfer.
Wyatt AS, Matia-Hernando P, Johnson AS, et al., 2014, Compression and amplification of SWIR single-cycle pulses for water window attosecond pulse generation
Wyatt AS, Matia-Hernando P, Johnson AS, et al., 2014, Compression and amplification of SWIR single-cycle pulses for water window attosecond pulse generation
Haessler S, Balciunas T, Fan G, et al., 2014, Optimization of quantum trajectories driven by strong-field waveforms, Physical Review X, Vol: 4, ISSN: 2160-3308
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