Self-referenced characterization of space-time couplings in near single-cycle laser pulses

We report on the characterization of space-time couplings in high energy sub-2-cycle 770nm laser pulses using a self-referencing single-shot method. Using spatially-encoded arrangement filter-based spectral phase interferometry for direct electric field reconstruction (SEA-F-SPIDER) we characterize few-cycle pulses with a wave-front rotation of 2.8x?10^11 rev/sec (1.38 mrad per half-cycle) and pulses with pulse front tilts ranging from to -0.33 fs/um to -3.03 fs/um.Comment: 6 pages, 6 figure

Synchronized pulses generated at 20 eV and 90 eV for attosecond pump-probe experiments

The development of attosecond pulses across different photon energies is an essential precursor to performing pump–probe attosecond experiments in complex systems, where the potential of attosecond science1 can be further developed2,3. We report the generation and characterization of synchronized extreme ultraviolet (90 eV) and vacuum ultraviolet (20 eV) pulses, generated simultaneously via high-harmonic generation. The vacuum ultraviolet pulses are well suited for pump–probe experiments that exploit the high photo-ionization cross-sections of many molecules in this spectral region4 as well as the higher photon flux due to the higher conversion efficiency of the high harmonic generation process at these energies5. We temporally characterized all pulses using the attosecond streaking technique6 and the FROG-CRAB retrieval method7. We report 576 ± 16 as pulses at 20 eV and 257 ± 21 as pulses at 90 eV. Our demonstration of synchronized attosecond pulses at different photon energies, which are inherently jitter-free due to the common-path geometry implemented, offers unprecedented possibilities for pump–probe studies

Correlation-Driven Transient Hole Dynamics Resolved in Space and Time in the Isopropanol Molecule

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 and termed 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 specific hole within the molecule. We report an investigation of the dynamics of inner valence hole states in isopropanol 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 ab initio theoretical treatment. We record the signature of transient hole dynamics and make the first tentative observation of dynamics driven by frustrated Auger-Meitner transitions. We verify that the 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 localized in space and time in molecules and thus to charge transfer phenomena that are fundamental in chemical and material physics

Spatio-temporal characterization of intense few-cycle 2 μm pulses

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)

Enhanced attosecond pulse generation in the vacuum ultraviolet using a two-colour driving field for high harmonic generation

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

Towards XUV pump-probe experiments in the femtosecond to sub-femtosecond regime: New measurement of the helium two-photon ionization cross-section

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

Attosecond sampling of arbitrary optical waveforms

Arbitrary waveform synthesis [1] offers the possibility to study and control electronic and nuclear processes with attosecond temporal resolution [2], and to enable 'sub-cycle' pulses and optimize high harmonic generation (HHG) [3, 4]. Appropriate metrology is critical to ensure the correct waveform is generated at the location of the experiment. Solutions to this measurement problem must deliver (a) adequate bandwidth; (b) sufficient efficiency; (c) sensitivity to phase across well-separated spectral components; (d) sensitivity to carrier-envelope phase (CEP); (e) reliable calibration procedures that can account for propagation between the measurement instrument and the experiment itself. Here we describe an experimental demonstration of the first all-optical method to characterize in-situ the real electric field of an arbitrary optical waveform based on HHG. © 2013 IEEE

Attosecond Resolved Interferometric Electric-field Sampling (ARIES)

This data set contains raw and processed data for the first proof-of-principle measurements of the ARIES technique. The method and results are fully described in the paper "Attosecond sampling of arbitrary optical waveforms", which has been accepted for publication in Optica (Feb 2016). All data has been saved as text documents for portability. For multidimensional arrays (>2 dimensions), the data has been split into multiple 2D array files with the filename appended by the extra dimension indices. For example, if the array "intensity" has dimension size [l1 x l2 x l3 x l4], it will be saved as files: intensity_1_1.dat = intensity(:, :, 1, 1) intensity_2_1.dat = intensity(:, :, 2, 1) intensity_1_2.dat = intensity(:, :, 1, 2) and so on ... The data has been zipped and compressed by folder. The contents.txt file lists the contents of all folders. The LabNotes.zip contains some MS Word documents created during the data acquisition, as well as some processing results. These notes are not complete, but contain useful information and help with orientation. The files Figx.zip contain all the data necessary to create the figures in the aforementioned paper. Units, where applicable, are indicated by a preceding double underscore in the filename, e.g. "Time__fs.dat" is the temporal axis in [fs]. Single letters preceded by an underscore should correspond to the sub-figure label. E.g. "Fig1/HHG_Int_b__au.dat" corresponds to the HHG spectral intensity in [au] of figure 1b. The dated zip files contain all the raw data, separated by date of acquisition. Some have been split even further according to the measurement type. Some zip files have been split into multiple parts "filename.zip.part-xx" which need to be joined together before extraction. The experiments consisted of two campaigns. The first campaign, performed in 2012, correspond to the first proof-of-principle results obtain in argon. After analysing these results and modifying the setup, the second campaign in 2013 was performed in neon. These data sets are extremely large due to saving the full 2D intensity image for each scan position. ** Generally each dataset consists of a scan of the delay between the TP and PP as a function of the TP wedge insertion. ** Data marked "CEP" correspond to small wedge insertions, thus modifying the TP CEP with little change in its temporal intensity. ** Data marked "Dispersion" or "DScan" correspond to large wedge insertions such that the TP temporal intensity changed significantly. ** Data marked "Glass" correspond to when a 1mm thick piece of fused silica was inserted into the TP beam to add significant amounts of dispersion. ** Files marked "Repeatability" should be repeated scans with identical settings (when identified by the same scan number on the same day). ** Files marked "SI" correspond to spectral interferometry measurements between the TP and PP. ** Files mark BP800-40 correspond to measurements made with a 40nm bandpass filter (BPF) centred at 800nm inserted into the TP beam. Files marked "R" had the BPF rotated, resulting in a blue-shift of the bandpass central wavelength. ** Data marked "FDI_CEPScan" correspond to HHG spectral intensity measurements of the PP alone as a function of the PP wedge insertion. These were used to optimize the compression of the PP to give the maximum cut-off energy and ensure a near-cosine PP. ** Data marked "PP_CEP" correspond to ARIES measurements as a function of the PP CEP. Note that changes in the PP CEP were also added to the TP CEP due to the experimental implementation