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We experimentally study the interaction between intense infrared few-cycle laser pulses and an ultrathin (∼2 µm) flat liquid sheet of isopropanol running in vacuum. We observe a rapid decline in transmission above a critical peak intensity of 50 TW/cm2 of the initially transparent liquid sheet, and the emission of a plume of material. We find both events are due to the creation of a surface plasma and are similar to processes observed in dielectric solids. After calculating the electron density for different laser peak intensities, we find an electron scattering rate of 0.3 fs-1 in liquid isopropanol to be consistent with our data. We study the dynamics of the plasma plume to find the expansion velocity of the plume front.

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.

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.

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 cmsup-1/sup. 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 cmsup-1/sup(0.65 eV), which we attribute to energy transfer from the Qsubx/subtransition 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.

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.

Wepresent the first measurement of the vectorial response of strongly dressed helium atoms probed by an attosecond pulse train (APT) polarised either parallel or perpendicular to the dressing field polarisation. The transient absorption is probed as a function of delay between the APT and the Linearly polarised 800 nmfield of peak intensity 1.3∗1014 W cm-2. The APT spans the photon energy range 1642 eV, covering the first ionisation energy of helium (24.59 eV). With parallel polarised dressing and probing fields, we observe modulations with periods of one half and one quarter of the dressing field period. When the polarisation of the dressing field is altered from parallel to perpendicular with respect to the APT polarisation we observe a large suppression in the Modulation depth of the above ionisation threshold absorption. In addition to this we present the intensity dependence of the harmonic modulation depth as a function of delay between the dressing and probe fields, with dressing field peak intensities ranging from 2∗1012 to 2∗1014 W cm-2.We compare our experimental results with a full-dimensional solution of the single-atom time-dependent (TD) Schrdinger equation obtained using the recently developed abinitio TDB-spline ADCmethod and find good qualitative agreement for the above threshold harmonics.

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 figures

We report the study of extended nanoripple structures formed during the interaction of high-intensity 3.5 fs pulses with a moving silicon wafer. The optimization of laser intensity (8×1013 W cm−2) and sample moving velocity (1 mm s−1) allowed the formation of long strips (∼5 mm) of homogeneous nanoripples along the whole area of laser ablation. The comparison of nanoripples produced on the silicon surfaces by few- and multi-cycle pulses is presented. We find that few-cycle pulses produce sharp and more homogenous structures than multi-cycle pulses.

High-order harmonic spectra are composed of a coherent sum of half-cycle emissions, the cut-off energy of which depend sensitively on different sub-cycle portions of the driving laser field. By selecting the correct focal geometry the half-cycle cut-off emissions can be preferentially selected over the lower energy plateau emissions through phase matching, such that they form macroscopic half-cycle cut-off features in the far-field spectrum. The energy of these macroscopic half-cycle cut-offs can then be used to retrieve the waveform of the driving laser field. The processes through which these macroscopic half-cycle cut-offs are formed and their applications, both for measuring the laser waveform and the generation of wavelength tunable isolated attosecond pulses, are reviewed in detail.

We present a technical review of a beamline built to perform pump-probe experiments with a temporal resolution of < 200 attosecond. This is designed specifically to use the technique of attosecond transient absorption spectroscopy (ATAS) to resolve ultra-fast electron dynamics in atoms and molecules. A non-collinear, interferometrically stable geometry is adopted to allow us to individually control the characteristics of each of the pump and probe arms independent from each other. With the use of an auxiliary interferometer to correct for long-term drifts between the pump and probe arms we measure better than 150as resolution for our time-corrected delay despite having separated beam paths of over 4m in length. In our first experiment we have focused on the time dependence of the electronic states of an atom in a strong laser field. An extreme ultra-violet (XUV) attosecond pulse train (APT) and a precisely synchronized 30fs IR pulse are used in this work. Delay-dependent absorption modulations are observed at even multiples (2 and 4) of the IR dressing field frequency as the pump-probe delay is scanned. We investigate the dependence of the 2ω order absorption modulation amplitude from the transient absorption of laser-dressed helium as the IR dressing field ellipticity is varied, and we discuss the issues in obtaining such results. We present qualitative data indicating a clear anisotropy in the response of the atom to an IR dressing field, and discuss how we will improve this measurement in future experiments.

In recent years the use of high-order harmonic radiation to create and control events on attosecond timescales has grown at a phenomenal rate. With the use of carrier-envelope phase (CEP) stabilization and few-cycle laser systems it is possible to probe physical processes on unprecedented timescales. Here, we report the first experimental observation of high-harmonic emission at individual half-cycles of a laser pulse. We show that these half-cycle emissions are extremely sensitive to the CEP, providing a route to a new single-shot measurement technique of the CEP. We use this technique to measure the CEP of an 8.5 fs pulse at a centre wavelength of 800 nm with an accuracy of 20 as (1 as=1×10−18 s). With appropriate spatio-spectral filtering of the harmonic spectra, our calculations show that we can isolate emission from an individual half-cycle cutoff, which corresponds to a single isolated attosecond pulse of duration

We have investigated experimentally the energy transmission and spectral broadening of 30-fs, 700-μJ laser pulses in a neon-filled, 250-μm inner diameter hollow fibre. We implement a differentially pumped fibre, where a vacuum is maintained at the fibre entrance, and compare this to a statically filled fibre. We obtain significantly higher transmission and increased spectral broadening in the differentially pumped case due to a reduction of ionisation defocusing at the fibre entrance. This arrangement provides a method for the generation of near-transform- limited pulses with smoothly varying pulse duration whilst maintaining constant pulse energy, by simple adjustment of the gas pressure. Compression of ∼450-μJ pulses from the differentially pumped fibre to a duration of 6.5 fs has been achieved for pulses with spectra spanning 650–900 nm, by use of negatively dispersive chirped mirrors.

The harmonic spectrum generated by a few-cycle laser pulse propagating through a gas jet is calculated. Two complementary atomic response models are used, one based on the time-dependent Schrodinger equation and the other on quantum orbits in which only a single pair of electron trajectories are taken into account. The role played by individual electron trajectories in determining particular features of the spectrum are considered and phase-matching maps are used to help understand their structure. A method based on this connection is proposed for diagnosing the carrier-envelope phase and the pulse duration of the incident laser field.

We outline a simple approach for determining plateau positions in harmonic spectra that demonstrates very clearly the requirement for carrier–envelope phase and intensity stabilization in the IR laser pulse for reliable attosecond pulse production. Neglecting the phase and intensity characteristics of the laser pulse will lead to large variations in the duration and number of sub-fs pulses produced via high harmonics cut-off windowing.

We report enhancement of third-harmonic generation in a nonlinear optical medium, prepared in maximum coherence by Stark-chirped rapid adiabatic passage (SCRAP). In this technique a strong off-resonant infrared radiation pulse induces an adiabatic passage process by sweeping the transition frequency of a two-photon transition in Krypton atoms through resonance with a near-resonant pump radiation pulse at 213 nm, appropriately delayed with respect to the infrared radiation. During the adiabatic passage process, a transient two-photon maximum coherence is induced, which beats with the pump laser frequency. Detrimental effects of Doppler broadening and collisional dephasing in the medium are reduced during the SCRAP process. The efficiency of third-harmonic generation, yielding vacuum-ultraviolet radiation at 71 nm is enhanced by more than one order of magnitude with respect to the case of conventional frequency conversion in an unprepared medium.

A novel scheme is analyzed for efficient generation of vacuum ultraviolet radiation through four-wave mixing processes assisted by the Stark chirp of two photon resonance. In this three-laser technique, a delayed-pulse of strong off-resonant infrared radiation sweeps the laser-induced Stark shift of a two-photon transition and facilitates maximum two-photon coherence induced by the second ultraviolet laser. A judiciously delayed third pulse beats with this coherence and generates short-wavelength radiation. A numerical simulation of transient processes, which ensure maximum coherence, including those leading to Stark-chirped rapid adiabatic passage, is presented. Potential high power and energy conversion efficiency of the weak long-wavelength radiation to the VUV range is shown for a difference-frequency scheme based on parametric amplification of this signal and strong four-wave coupling at maximum atomic coherence.

Quasifree field-driven electron trajectories are a key element of strong-field dynamics. Upon recollision with the parent ion, the energy transferred from the field to the electron may be released as attosecond-duration extreme ultaviolet emission in the process of high-harmonic generation. The conventional sinusoidal driver fields set limitations on the maximum value of this energy transfer and the efficient return of the launched electron trajectories. It has been predicted that these limits can be significantly exceeded by an appropriately ramped-up cycle shape [L. E. Chipperfield et al., Phys. Rev. Lett. 102, 063003 (2009)]. Here, we present an experimental realization of similar cycle-shaped waveforms and demonstrate control of the high-harmonic generation process on the single-atom quantum level via attosecond steering of the electron trajectories. With our improved optical cycles, we boost the field ionization launching the electron trajectories, increase the subsequent field-to-electron energy transfer, and reduce the trajectory duration. We demonstrate, in realistic experimental conditions, 2 orders of magnitude enhancement of the generated extreme ultraviolet flux together with an increased spectral extension. This application, which is only one example of what can be achieved with cycle-shaped high-field light waves, has significant implications for attosecond spectroscopy and molecular self-probing.

We generate 9 fs 1.7 μm 300 μJ pulses by hollow fiber compression. Complete 3D simulations show good agreement across a range of fiber pressures and elucidate the role of shock formation and Kerr effect saturation.

We demonstrate attosecond streaking on thin Au films. This is the first streaking measurement on Au, and also the first demonstration of streaking on a non-crystalline, non-UHV-prepared sample.

We investigate the performance and carrier-envelope phase (CEP) stability of hollow- fiber pulse compression for high-energy, close to single-cycle duration pulses. We find the onset of an ionization-induced CEP instability, which saturates above 1.25mJ.

The interaction of high-intensity short pulse (fs) lasers with atomic or molecular vapors permits the conversion of visible light to intense coherent radiation in the vacuum ultraviolet spectral region. We demonstrate sum frequency mixing of a high-intensity short pulse (fs) laser with a conventional long pulse (ns) laser to extend the accessible wavelength range of harmonic generation. The mixing process does not rely on meeting resonances and can in principle be implemented with any intense short pulse (fs) laser system in any nonlinear medium. The efficiency of the sum frequency mixing process is comparable to the efficiency of harmonic generation of a similar wavelength with the high-intensity short pulse (fs) laser alone. We propose the application of conventional tunable long pulse (ns) lasers to permit the generation of broadly tunable picosecond radiation in the vacuum ultraviolet.

We have studied the generation of vacuum ultraviolet radiation (at 123.6 nm) produced in a resonant four-wave-mixing scheme in krypton, enhanced by electromagnetically induced transparency. The interplay between the non-linear susceptibility (governing the wave-mixing), the linear susceptibility (governing the absorption and dispersion), and the density-length product was examined both experimentally and numerically. We observe favourable scaling of the yield with density-length product (NL) up to a value of 5×10 16 cm −2 . Above this NL value the yield decreases due to the background wave-vector mismatch (Δ k resid ), which arises from the additional atomic energy levels outside the three considered in the EIT enhanced mixing scheme. Our results suggest that further enhancements in frequency up-conversion can be achieved by employing a buffer gas as a phase matching agent.

The tunnelling of a bound electron out of an atom in a laser field is a well-known quantum-mechanical process. But it happens very quickly, and it takes some fast work with X-rays and lasers to see it in action.

The International Year of Light (IYL) in 2015 is a unique opportunity to celebrate and broadcast the enormous contribution of optics to science, technology and culture. The Journal of Modern Optics...

Summary form only given. 1.7 cycles midIR pulse has been measured via a tunable SEA-F-SPIDER arrangement providing both temporal and spatial characterisation. The intrinsic CEP stability of the pulse is monitored and stabilised from a simple interferometric measurement.A significant part of future development in attosecond science [1] and especially molecular high harmonic generation spectroscopy [2] is likely to require the use of intense and ultrashort infrared laser pulses in the mid-infrared (mid-IR) spectral range. Secondary sources based on Ti:Sapphire laser pumped Optical Parametric Amplifier (OPA) in nonlinear crystals are readily available as commercial systems and their extension to few-cycles mid-IR sources have been demonstrated [3,4]. MidIR pulses at 1.7um are generated by self phase modulation (SPM) of the idler pulse of a HE-TOPAS (Light Conversion) in an Argon filled hollow core fibre and subsequent compression in Fused Silica. The carrier envelope phase (CEP) of such short pulses is of prime interest for strong field physics experiment. Its pulse to pulse passive stability is here assured by the difference frequency generation mechanism in the last OPA stage [4]. Providing a stable pump source (~1% pulse to pulse energy fluctuation) the main source of CEP fluctuation is due to the temporal interferometric jitter between pump and seed in the DFG process.Our temporal characterisation relies on SEA-SPIDER [6] with direct spectral filtering for ancilla preparation (SEA-F-SPIDER [7,8]). A spatio-temporal reconstruction of our single cycle pulse is shown in fig.1 (inset) from which a lineout has been extracted (red curve) and compared to the Fourier Limit (in black). Apulse duration of 9.9fs has been obtained representing 1.7 cycles at 1.7um. Interference fringes at ~700nm are produced from SHG of the seed for one part and SPM of the pump in the last OPA crystal for the other part. The interference of these two almost balanced paths (about 3 meters each) creates fringes that are stabilised and controlled by a piezo actuator added on the pump arm. The evolution of the interferogram as a function of time with a slow loop stabilisation turned on is visible on figure 1 b) for different relative set phases. The stability in each interval is excellent and on the order of 100 mrad standard deviation. Since the stability of this interferometer is directly coupled to the CEP stability of the generated pulse, this measurement is a monitor of an important source of the CEP fluctuations.

We report on high-order-harmonic generation in nanoparticle-containing laser ablation plasmas using a Ti:sapphire driving laser at a repetition rate of 1 kHz and on the relation of the harmonic signals with the morphological and spectroscopic characteristics of the ablation deposits. The study of the deposits has allowed the definition of ablation conditions, leading to the generation of a plasma containing nanoparticles of similar sizes to the ones used as target material. The corresponding plasma plumes lead to efficient conversion of the IR photons towards the short-wavelength range through high-order harmonic generation and show superior performance to those corresponding to bulk targets of the same metallic element. © 2013 American Physical Society.

We have investigated the generation of the high order harmonics (q=5-15) of a 150 fs Ti:S laser operating at 780 nm in the intensity range 2.5*1013-1015 W cm-2. We report, we believe for the first time, high order harmonic generation from gases of pure organic molecules (butane C4H10 and 1,3-butadiene C4H6). By comparison with xenon under nominally the same irradiance and gas density conditions, we infer that the conversion efficiency in the molecular systems is approximately an order of magnitude less than that from xenon. We report broad similarity between butane and butadiene under these conditions, with butane being more efficient at higher irradiances. In contrast, at the lowest irradiances investigated (2.5*1013 W cm-2) harmonic generation in butadiene becomes relatively more efficient, when compared to butane, which we tentatively attribute to the presence of the pi delocalized electrons in this molecule.

We present a variant of spatially encoded spectral shearing interferometry for measuring two-dimensional spatio-temporal slices of few-cycle pulses centered around 2 μm. 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).

We report studies of high-order harmonic generation in laser-produced manganese plasmas using sub-4-fs drive laser pulses. The measured spectra exhibit resonant enhancement of a small spectral region of about 2.5 eV width around the 31st harmonic (~50eV). The intensity contrast relative to the directly adjacent harmonics exceeds one order of magnitude. This finding is in sharp contrast to the results reported previously for multi-cycle laser pulses [Physical Review A 76, 023831 (2007)]. Theoretical modelling suggests that the enhanced harmonic emission forms an isolated sub-femtosecond pulse.

We report on the spatially resolved full amplitude and phase characterization of mid-infrared high intensity laser pulses generated in a three stage OPA. We use a spatially-encoded arrangement (SEA-)SPIDER with spectral filters for ancilla generation for spatially resolved characterization. Using five interchangeable filter sets we are able to characterize pulses from 1 to 2{\mu}m with one single device with minimal adjustments., Comment: 6 pages, 5 figures

We report on the observation of enhanced high harmonics from a carbon plasma using sub-5-fs laser pulses. The efficiency of harmonic generation in the range of 14\char21{}25 eV was up to five times higher in the case of a plasma medium (graphite ablation) compared with gas (argon) under similar experimental conditions. The harmonic enhancement can be attributed to the presence of carbon nanoparticles in the ablation plumes.

We report on the spatially resolved full amplitude and phase characterization of high intensity few-cycle laser pulses. The sub-4-fs pulses are generated in a single stage hollow core fiber system with subsequent compression by ultrabroadband chirped mirrors. We use a spatially-encoded arrangement(SEA-)SPIDER with spectral filters for ancilla generation to fully characterize the sub-4-fs pulses with spatial resolution in a single shot.

Recently the use of isolated attosecond pulses has allow unprecedented temporal resolution of charge motion in gases and condensed matter [1,2]. A surface science apparatus has been constructed to allow the ultrafast charge dynamics on rough and structured surfaces to be investigated. The system is connected to the Attosecond source at Imperial College allowing isolated attosecond bursts of XUV radiation to be used as a probe Fig.2.

We examine trajectory selection and resulting yield modulation in high harmonic generation using a multicolor field composed of an 800nm fundamental and its perpendicularly polarized second harmonic.

We report on our recent development of a femtosecond infrared laser system based on self-phase-stabilized seed by difference-frequency generation of supercontinuum obtained with so-called hollow fiber compression technique and two-stage optical parametric amplification. After the final amplifier, we obtained pulses with duration of 500 μJ and as a first demonstration of this new laser system, we generated high-harmonics up to 47th order in a tube target filled with Xe gas.

Reported is the spectral shifting observed when a ≈ 1 ps, 1 μm laser pulse is focussed into a cell containing argon at pressures from 0–10 bar. Focal intensities of 1–5×10 15 W cm -2 would be expected in vacuum for the ‖/8 focussing used. Instead evidence is found in the spectra of a significant decrease in the focal intensity reached when higher gas pressures are used. For the first time the spatial distribution of the shifted spectra is investigated. Spectral shifts are found to increase off-axis in the transmitted beam profile. The distributions show many peaks and minima and contain much extra detail. A two-dimensional numerical propagation model shows good general agreement with the experimental results.

We report the observation of harmonics up to the 119th in helium, generated using a 1.053-\ensuremath{\mu}m, 1-ps chirped-pulse-amplification laser at intensities up to 3\ifmmode\times\else\texttimes\fi{}${10}^{14}$ W/${\mathrm{cm}}^{2}$, and the measurement of their far-field spatial distribution. Complex spatial distributions are found for harmonics in the plateau region and near the cutoff; their angular distribution narrows to approximately that predicted by lowest-order perturbation theory.

Ultrafast science has begun to tackle the measurement of electronic and chemical processes taking place on the few-femtosecond-to-attosecond timescale. This field requires high-power, extremely short-duration laser pulses. Here we review progress towards the generation of such pulses by Raman scattering in a medium whose component molecules oscillate in phase, which modulates the optical polarizability of the medium and generates high-order Raman sidebands on a field propagating through it. This process may occur with high efficiency and thus lead to sufficient bandwidth for supporting few-femtosecond to attosecond pulses. Significant progress has recently been made in the use of this technique to deliver useable ultrashort pulses in the visible to ultraviolet regions of the spectrum.

We demonstrate control of short and long quantum trajectories in high harmonic emission through the use of an orthogonally polarized two-color field. By controlling the relative phase ϕ between the two fields we show via classical and quantum calculations that we can steer the two-dimensional trajectories to return, or not, to the core and so control the relative strength of the short or long quantum trajectory contribution. In experiments, we demonstrate that this leads to robust control over the trajectory contributions using a drive field from a femtosecond laser composed of the fundamental ω at 800 nm (intensity ∼1.2×10(14) W cm(-2)) and its weaker orthogonally polarized second harmonic 2ω (intensity ∼0.3×10(14) W cm(-2)) with the relative phase between the ω and 2ω fields varied simply by tilting a fused silica plate. This is the first demonstration of short and long quantum trajectory control at the single-atom level.

In this contribution we present a method for multi-color waveform synthesis in the IR spectral region using optical parametric amplification (OPA). With this synthesizer, we demonstrate shot-to-shot reproducible pulses formed by a combination of incommensurate frequencies. Control of the reproducible multicolor waveform generation is demonstrated by using different CEP sensitive methods: i) nonlinear spectral interferometry; ii) directional ATI electron emission; iii) THz emission by tunneling microcurrent.

We report observations and analysis of high harmonic generation driven by a superposition of fields at 1290 nm and 780 nm. These fields are not commensurate in frequency, as in previous experiments such as Ref. [1], and the superposition leads to an increase in the yield of the mid-plateau harmonics of more than two orders of magnitude compared to using the 1290 nm field alone. Significant extension of the cut-off photon energy is seen even by adding only a small amount of the 780 nm field. Fig. 1 plots the observed yield enhancements against harmonic energy and scanned over the temporal delay between the peaks of the two pulse envelopes. The figure shows two different intensity ratios, as stated in the caption. In both cases yield enhancement of up to two orders of magnitude is seen below 40 eV, together with smaller enhancements up to 80 eV, the limit of the MCP detector. This is a promising route to provide a greater photon number in attosecond pulse production [2], for applications in XUV imaging and time-resolved experiments [3].

In the few-cycle regime, the light-matter interaction becomes extremely sensitive to the pulse shape and it is highly advantageous to use techniques such as frequency resolved optical gating (FROG) and spectral phase interferometry for direct electric field reconstruction (SPIDER) to obtain a full amplitude and phase characterization of the pulse. A unique advantage of SPIDER is a direct and rapid algebraic field reconstruction that makes it well-suited for online monitoring and optimization of the pulse. High intensity few-cycle pulses are typically generated by nonlinear spectral broadening in a gas-filled hollow core fiber (HCF) or a filament followed by compression using chirped mirrors. Using HCFs, pulse energies up to 5 mJ and pulse durations below 4 fs [1] have been previously demonstrated. Both these methods can lead to pulses with spatially-dependent temporal properties, but to-date, only a few spatially resolved pulse characterization measurements have been made and only for many-cycle pulses [2, 3].

High-order harmonic generation in laser-produced plasma was demonstrated on metal surfaces using a high pulse repetition rate laser (1 kHz). It was found that if sufficiently thick bulk targets were used thermal conduction was sufficient to prevent any deterioration in the metal plasma plume production at this repetition rate. Under appropriate conditions harmonic yields were found to remain stable for >105 laser shots without the need to move the target. The high repetition rate allowed both short and long electron trajectories to be clearly identified during harmonic generation from the metal plasmas. © 2011 Taylor & Francis., This research was supported by a Marie Curie International Incoming Fellowship within the 7th European Community Framework Programme, EPSRC programme (Grant EP/ E028063/1), and FASTQUAST ITN. M.E. Lo´pez-Arias acknowledges CSIC for a JAE-pre contract.

The Artemis facility for ultrafast XUV science is constructed around a high average power carrier-envelope phasestabilised system, which is used to generate tuneable pulses across a wavelength range spanning the UV to the far infrared, few-cycle pulses at 800nm and short pulses of XUV radiation produced through high harmonic generation. The XUV pulses can be delivered to interaction stations for materials science and atomic and molecular physics and chemistry through two vacuum beamlines for broadband XUV or narrow-band tuneable XUV pulses. The novel XUV monochromator provides bandwidth selection and tunability while preserving the pulse duration to within 10 fs. Measurements of the XUV pulse duration using an XUV-pump IR-probe technique demonstrate that the XUV pulselength is below 30 fs for a 28 fs drive laser pulse. The materials science station, which contains a hemispherical electron analyser and five-axis manipulator cooled to 14K, is optimised for photoemission experiments with the XUV. The end-station for atomic and molecular physics and chemistry includes a velocity-map imaging detector and molecular beam source for gas-phase experiments. The facility is now fully operational and open to UK and European users for twenty weeks per year. Some of the key new scientific results obtained on the facility include: the extension of HHG imaging spectroscopy to the mid-infrared; a technique for enhancing the conversion efficiency of the XUV by combining two laser fields with non-harmonically related wavelengths; and observation of D3+ photodissociation in intense laser fields.

We describe a simple, high throughput, LiF prism monochromator for the vacuum ultraviolet (VUV). The instrument throughput is 30% at 145 nm and the output can be tuned within the range 120–185 nm. The very high dispersion of LiF in the VUV means that neither narrow slits nor high precision are required. The suitability of this instrument for separation of coherent VUV radiation, generated by four-wave mixing, from the intense fundamental laser radiation (at 212 nm and the visible) is demonstrated. General advantages in throughput, polarization and resistance to radiation damage of such a prism instrument compared to a diffraction grating monochromator are discussed.

Understanding the role of coherent electronic motion is expected to resolve general questions of importance in macromolecular energy transfer. We demonstrate a novel nonlinear optical method, angle-resolved coherent wave mixing, that separates out coherently coupled electronic transitions and energy transfers in an instantaneous two-dimensional mapping. Angular resolution of the signal is achieved by using millimeter laser beam waists at the sample and by signal relay to the far field; for this we use a high energy, ultrabroadband hollow fiber laser source. We reveal quantum electronic beating with a time-ordered selection of transition energies in a photosynthetic complex.

We describe a new study of the odd-parity doubly excited spectrum of Ca I, in which a tunable coherent VUV source was used to scan over an energy range previously investigated by classical spectroscopy using synchrotron radiation. A vast improvement in the quality of the data, especially as regards the available spectral resolution, results from the use of a four-wave mixing source and enables the comparison between theory and experiment to be pushed further than ever before for doubly excited states in alkaline-earth spectra. Some remaining limitations of the theoretical computations are brought to light and discussed.

Techniques for measuring the sub-optical cycle electron dynamics from the HHG spectrum are identified and control methods to optimize HHG, which may soon be used in practice, are treated theoretically.