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We have developed dielectric-lined rectangular waveguide structures for terahertz (THz)-driven ultrafast deflection of 100 keV electron beams. The structures were designed to achieve THz phase velocity matching with co-propagating electron bunches. The phase-matching capability was experimentally confirmed through time-frequency analysis of the broadband coherent THz transmission measured by electro-optic sampling. The analysis determined both the frequency-dependent propagation constants in the electron interaction region and the propagation characteristics of the integrated THz tapered coupler.

An experimental area has been constructed dedicated to investigating the effectiveness of numerous structures at mediating terahertz-electron interactions. Initial experiments will involve terahertz driven bunch compression and longitudinal diagnostics with terahertz driven accelerating structures to follow.

The recent emergence of spintronic terahertz (THz) emitters has provided a low-cost source of high field-strength, broadband THz radiation, exploiting the laser-induced electron spin properties in magnetic multi-layers to produce gap-free emission covering 1-30 THz and electric fields up to 300 kV/cm. An interesting property of spintronic emitters is that they have been shown to generate THz radiation polarized perpendicular to the applied magnetic field and independent of the pump laser polarization. We exploit this magnetic field-dependent emission process to create arbitrary terahertz polarization profiles. We show that by applying a specific magnetic field pattern to the source, it is possible to generate a quadrupole-like THz polarization profile. Measurements of the THz electric field at the focus of the beam revealed a polarity flip in the transverse profile of the quadrupole-like mode with a resulting strong, on-axis longitudinal component of 17.7 kV/cm.

Linear accelerators operating at millimeter or sub-terahertz frequencies and short pulse duration have the advantages of lower power consumption and high repetition rate. In this paper planar metallic accelerating structures with different modes operating at 210 GHz were designed. A tolerance study was also carried out to determine the sensitivities of the geometric parameters to the wakefield acceleration performance. The generated Wakefield was simulated using the beam parameter of the Compact Linear Advanced Research Accelerator (CLARA) test facility at Daresbury Laboratory. For a 55 MeV single electron bunch with charge of 250 pC and a bunch length of 0.27 mm (0.9 ps), an equivalent acceleration gradient of 20 MV/m was achieved in the simulation. The relatively modest acceleration gradient was limited by the charge in a single bunch. The acceleration gradient could be further improved by using a bunch train which has larger total bunch charge. From the simulation, the acceleration gradient of 100 MV/m can be generated when it is driven by a 10-bunch beam train.

Advanced acceleration technologies are receiving considerable interest in order to miniaturize future particle accelerators. One such technology is the dual-grating dielectric structures, which can support accelerating fields one to two orders of magnitude higher than the metal RF cavities in conventional accelerators. This opens up the possibility of enabling high accelerating gradients of up to several GV/m. This paper investigates numerically a quartz dual-grating structure which is driven by THz pulses to accelerate electrons. Geometry optimizations are carried out to achieve the trade-offs between accelerating gradient and vacuum channel gap. A realistic electron bunch available from the future Compact Linear Accelerator for Research and Applications (CLARA) is loaded into an optimized 100-period dual-grating structure for a detailed wakefield study. A THz pulse is then employed to interact with this CLARA bunch in the optimized structure. The computed beam quality is analyzed in terms of emittance, energy spread and loaded accelerating gradient. The simulations show that an accelerating gradient of 348 ± 12 MV/m with an emittance growth of 3.0% can be obtained.

We will present the first results from the CLARA research facility at Daresbury Laboratory demonstrating terahertz-driven acceleration of a relativistic 35 MeV electron beam. A polarization-tailored, frequency-tunable, narrowband terahertz source was used to directly excite the longitudinal accelerating mode of a dielectric-lined waveguide structure for collinear phase-velocity-matched THz-electron interaction.

We report on the generation of a terahertz (THz) beam with a quasi-TEM 01 mode by exploiting the interferometric recombination of two linearly polarized emitters in a combined spintronic source. The generated THz beam was used to characterize the accelerating mode of a dielectric-lined waveguide (DLW) to inform on the recent demonstration of relativistic electron beam manipulation achieved with this THz-driven DLW at the CLARA research facility at Daresbury Laboratory.

The temporal and spatial evolution of single-cycle THz pulses travelling across a dielectric boundary with effective surface velocity below $c$ has been examined. The resulting subluminal evanescent waves in the near field vacuum region are potential drivers of particle accelerators. The electro-optic temporal and spatial imaging of the THz pulses emitted from the surface were measured in the near field, as a function of distance from the dielectric boundary, and reveal both temporal broadening and field decay that is dependent on the effective velocity of the wave in the plane of the boundary.

Dielectric structures driven by laser-generated terahertz (THz) pulses may hold the key to overcoming the technological limitations of conventional particle accelerators and with recent experimental demonstrations of acceleration, compression and streaking of low-energy (sub-100 keV) electron beams, operation at relativistic beam energies is now essential to realize the full potential of THz-driven structures. We present the first THz-driven linear acceleration of relativistic 35 MeV electron bunches, exploiting the collinear excitation of a dielectric-lined waveguide driven by the longitudinal electric field component of polarization-tailored, narrowband THz pulses. Our results pave the way to unprecedented control over relativistic electron beams, providing bunch compression for ultrafast electron diffraction, energy manipulation for bunch diagnostics, and ultimately delivering high-field gradients for compact THz-driven particle acceleration., 8 pages, 4 figures

We report on the characterisation of an x-ray source, generated by a laser-driven plasma wakefield accelerator. The spectrum of the optimised source was consistent with an on-axis synchrotron spectrum with a critical energy of 13.8 − 1.9 + 2.2 keV and the number of photons per pulse generated above 1 keV was calculated to be 6 − 0.9 + 1.2 × 10 9 . The x-ray beam was used to image a resolution grid placed 37 cm from the source, which gave a measured spatial resolution of 4 µm × 5 µm. The inferred emission region had a radius and length of 0.5 ± 0.2 µm and 3.2 ± 0.9 mm respectively. It was also observed that laser damage to the exit aperture of the gas cell led to a reduction in the accelerated electron beam charge and a corresponding reduction in x-ray flux due to the change in the plasma density profile.

Electro-optic (EO) techniques are increasingly used for longitudinal bunch profile measurements. A bunch profile monitor, based on electro-optic spectral decoding (EOSD), has been developed and demonstrated on the CALIFES beam line at CERN. The EO response is analysed using a frequency domain description, and two methods for extraction of absolute Coulomb field strengths from the electron bunch are demonstrated. Measurements at field strengths up to 1.3 MV/m agree with the expectation based on independent charge measurements.

Terahertz-driven dielectric-lined waveguides (DLWs) have uses in electron manipulation; in particular deflection, acceleration, and focussing. A rectangular DLW has been optimised for deflection of 100 keV electrons using a THz pulse with a centre frequency 0.5 THz. Electron-THz interaction and the effect of electron bunch injection timing on maximising deflection is presented. DLWs and corrugated waveguides are compared to discuss relative advantages and disadvantages., 4 pages plus references. 8 figures (2 figures have two separate sub-figures giving 10 total). Proceedings of EEAC17, submitted to NIM-A

Dielectric laser-driven accelerators (DLAs) can provide high accelerating gradients in the GV/m range due to their having higher breakdown thresholds than metals, which opens the way for the miniaturization of the next generation of particle accelerator facilities. Two kinds of scheme, the addition of a Bragg reflector and the use of pulse-front-tilted (PFT) laser illumination, have been studied separately to improve the energy efficiency for dual-grating DLAs. The Bragg reflector enhances the accelerating gradient of the structure, while the PFT increases the effective interaction length. In this paper, we investigate numerically the advantages of using the two schemes in conjunction. Our calculations show that, for a 100-period structure with a period of 2 micrometer, such a design effectively increases the energy gain by more than 100 % when compared to employing the Bragg reflector with a normal laser, and by about 50 % when using standard structures with a PFT laser. A total energy gain of as much as 2.6 MeV can be obtained for a PFT laser beam when illuminating a 2000-period dual-grating structure with a Bragg reflector., Comment: 7 pages, 4 Figures, Proceedings of EAAC2017 Conference

We consider the non-linear generation of THz with tilted pulse-fronts in three dimensions and show that, contrary to the widely held expectations, coherent phase matching can be obtained for pulse-front tilt angles other the Cherenkov angle.

We demonstrate that a magnetic field pattern can successfully manipulate the magnetic state of a spintronic terahertz emitter, opening up the possibility to directly tailor arbitrary terahertz polarization modes for novel applications.

We report on the transmission properties of a single-cycle terahertz pulse through a rectangular-shape dielectric-lined waveguide designed for terahertz-driven manipulation of 100 keV electrons.

The original version of this Article contained an error in the abstract, referring to “multi-megawatt-per-metre” instead of “multi-megavolt-per-metre”. This has now been corrected in both the PDF and HTML versions of the Article.

Terahertz(THz)-driven dielectric-lined waveguides have applications in electron manipulation, particularly acceleration, as the use of dielectric allows for phase velocities below the speed of light. However matching a single frequency to the correct velocity does not maximise electron-THz interaction; waveguide dispersion typically results in an unmatched group velocity and so the pulse envelope of a short THz pulse changes along the length of the structure. This reduces field amplitude and therefore accelerating gradient as the envelope propagates at a different velocity to the electron. The effect on net acceleration is demonstrated via an example of a structure excited by a THz pulse of different temporal lengths.

Dielectric laser-driven accelerators (DLAs) based on grating structures are considered to be one of the most promising technologies to reduce the size and cost of future particle accelerators. They offer high accelerating gradients of up to several GV/m in combination with mature lithographic techniques for structure fabrication. This paper numerically investigates the beam quality for acceleration of electrons in a realistic dual-grating DLA. In our simulations, we use beam parameters of the future Compact Linear Accelerator for Research and Applications facility to load an electron bunch into an optimized 100-period dual-grating structure where it interacts with a realistic laser pulse. The emittance, energy spread, and loaded accelerating gradient for modulated electrons are then analyzed in detail. Results from simulations show that an accelerating gradient of up to 1.13 ± 0.15 GV/m with an extremely small emittance growth, 3.6%, can be expected.

The sub-luminal phase velocity of electromagnetic waves in free space is generally unobtainable, being closely linked to forbidden faster than light group velocities. The requirement of sub-luminal phase-velocity in laser-driven particle acceleration schemes imposes a limit on the total acceleration achievable in free space, and necessitates the use of dispersive structures or waveguides for extending the field-particle interaction. We demonstrate a travelling source approach that overcomes the sub-luminal propagation limits. The approach exploits ultrafast optical sources with slow group velocity propagation, and a group-to-phase front conversion through nonlinear optical interaction. The concept is demonstrated with two terahertz generation processes, nonlinear optical rectification and current-surge rectification. We report measurements of longitudinally polarised single-cycle electric fields with phase and group velocity between 0.77c and 1.75c. The ability to scale to multi-megavolt-per-metre field strengths is demonstrated. Our approach paves the way towards the realisation of cheap and compact particle accelerators with femtosecond scale control of particles., Controlled generation of terahertz radiation with subluminal phase velocities is a key issue in laser-driven particle acceleration. Here, the authors demonstrate a travelling-source approach utilizing the group-to-phase front conversion to overcome the sub-luminal propagation limit.

We demonstrate the generation of terahertz radiation pulses with a sub-luminal phase velocity using ZnTe. The pulses are near-single cycle and have been measured over a distance of 4.8 mm. Tunable phase velocities as low as (0.77 ± 0.01) c have been measured and the method employed can readily be adapted to produce velocities over a wider range.

We report a technique for the single-shot measurement of single-cycle THz radiation without the need for ultrashort laser pulses. The nonlinear mixing between a narrow linewidth laser and a THz pulse encodes the THz temporal profile into the envelope of a new optical pulse. The preservation of temporal and spectral information in this process enables retrieval of the THz pulse from a standard FROG measurement of the new optical signal. A system has been built which includes a broadband OPA for amplification of the low energy transposed pulse to a level compatible with single-shot FROG methods. The technique should prove essential in the characterization of ultrashort THz pulses that are generated with large shot-to-shot jitter.

In a fixed-field alternating-gradient (FFAG) accelerator, eliminating pulsed magnet operation permits rapid acceleration to synchrotron energies, but with a much higher beam-pulse repetition rate. Conceived in the 1950s, FFAGs are enjoying renewed interest, fuelled by the need to rapidly accelerate unstable muons for future high-energy physics colliders. Until now a 'scaling' principle has been applied to avoid beam blow-up and loss. Removing this restriction produces a new breed of FFAG, a non-scaling variant, allowing powerful advances in machine characteristics. We report on the first non-scaling FFAG, in which orbits are compacted to within 10 mm in radius over an electron momentum range of 12-18 MeV/c. In this strictly linear-gradient FFAG, unstable beam regions are crossed, but acceleration via a novel serpentine channel is so rapid that no significant beam disruption is observed. This result has significant implications for future particle accelerators, particularly muon and high-intensity proton accelerators. © 2012 Macmillan Publishers Limited. All rights reserved.

Due to the combination of fixed magnetic field operation with strong focusing, non-scaling FFAGs have a significant potential for future particle accelerator applications. However, this technology has a number of unique features, which must be fully studied before this potential can be realised. To do this, a proof-of-principle non-scaling FFAG, called EMMA – Electron Model for Many Applications – has been constructed at the STFC Daresbury Laboratory in the UK. It has been designed by an international collaboration of accelerator scientists and engineers. It will demonstrate the principle of non-scaling FFAGs and be used to study the features of this type of accelerator in detail.

Inverse Compton scattering is a promising method to implement a high-brightness, ultra-short, energy tuneable X-ray source at accelerator facilities and at laser facilities using laser wake-field acceleration. We have developed an inverse Compton X-ray source driven by the multi-10-TW laser installed at Daresbury Laboratory. Polarized X-ray pulses will be generated through the interaction of laser pulses with electron bunches delivered by the energy recovery linac commissioned at the ALICE facility with spectral peaks ranging from 0.4 to 12 A, depending on the electron bunch energy and the scattering geometry. X-ray pulses containing up to 107 photons per pulse will be created from head-on collisions, with a pulse duration comparable to the incoming electron bunch length. For transverse collisions the laser pulse transit time defines the X-ray pulse duration. The peak spectral brightness is predicted to be up to 1021 photon/(s mm2 mrad2 0.1% Δλ/λ). Called COBALD, this source will be initially used as a short-pulse diagnostic for the ALICE electron beam and will explore the extreme challenges of photon/electron beam synchronization, which is a fundamental requirement for all conventional accelerator and laser wake-field-acceleration-based sources.

The χ(2) interaction between an intense terahertz (THz) pulse and a weak optical probe is addressed, and a general solution obtained for the situation of an undepleted THz wave. It is shown that the common description of a phase retardation proportional to the THz electric field strength breaks down in strong-field conditions, unless the THz field is suitably slowly varying. The solution is obtained from a consistent description of sum- and difference-frequency generation driven by the THz field, the input optical field, and all optical fields generated through the interaction itself. For an interaction between monochromatic THz and optical waves a minimum of four waves (three optical and one THz) need be considered in the weak-field limit; higher numbers of waves are needed at higher fields, with the extent of the required optical spectrum dependent on field strength, phase matching, and interaction length.

We demonstrate that full temporal characterisation of few-cycle electromagnetic pulses, including retrieval of the carrier envelope phase (CEP), can be directly obtained from Frequency Resolved Optical Gating (FROG) techniques in which the interference between non-linear frequency mixing processes is resolved. We derive a framework for this scheme, defined Real Domain-FROG (ReD-FROG), as applied to the cases of interference between sum and difference frequency components and between fundamental and sum/difference frequency components. A successful numerical demonstration of ReD-FROG as applied to the case of a self-referenced measurement is provided. A proof-of-principle experiment is performed in which the CEP of a single-cycle THz pulse is accurately obtained and demonstrates the possibility for THz detection beyond the bandwidth limitations of electro-optic sampling., Comment: 7 pages, 4 figures. To be submitted for publication in Optics Express, January 2015

Electro-optic (EO) detection of relativistic Coulomb fields offers a method for non-destructive longitudinal profile measurements of ultrashort bunches. Techniques for single-shot EO characterisation of Coulomb fields which have been developed or demonstrated at the FELIX free electron laser (FEL) facility are discussed. In addition, recent FELIX experiments have used single-shot electro-optic detection to measure the temporal profile of the far-infrared electric field pulse of coherent synchrotron radiation (CSR), initial results of which are reported here. Such time-resolved CSR measurements have the potential for a completely non-invasive bunch longitudinal profile determination, without the ambiguity in profile that is present in CSR spectral measurements.

The interaction of ultrashort laser pulses with krypton clusters at intensity up to 1.3×1018 Wcm−2 has been investigated. Intense Kα and Kβ emission from krypton at 12.66 and 14.1 keV, respectively, has been observed using conventional solid state x-ray detectors. The measured x-ray spectra have broad bremsstrahlung continuum reaching to photon energies up to 45 keV, with evidence that approximately 10% of electrons that are heated to very high electron temperatures, which is consistent with a two-temperature electron distribution. This is ascribed to the presence of a hot electron population, similar to that found in laser–solid interactions. The highest laser energy to x-ray conversion efficiency observed is 9.2×10−7, which is equivalent to 45 nJ x-ray pulse energy from the 12.66 keV krypton Kα transition.

Observations of a directional asymmetry in the sub-ps THz radiation generated from ultrafast excitation of biased GaAs are presented. This asymmetry is inconsistent with the long standing and widely accepted surface-layer current-surge description of the THz emission process. A model based on propagating carrier excitation fronts during spectral-hole-burning is proposed to explain these observations. This model introduces new roles for the semiconductor optical and carrier transport properties in determining the efficiency of the THz generation process.

X rays emitted from Kr clusters illuminated by a femtosecond laser have been observed over a wide spectral region from 3 keV to 15 keV. The measured spectra are characterized by a broad bremsstrahlung continuum and Kα, β lines at 12.66 keV and 14.1 keV. To the best of the authors' knowledge, this is the first observation of Kα, β emission from laser-heated Kr clusters. The bremsstrahlung continuum arising from collisions in the plasma implies a population of hot electrons consistent with a temperature of several kiloelectron volts. The absolute X-ray yield in the 3–15 keV region is found to be of the order of 107 photons per laser pulse. The plasma temperature, estimated from the continuum part of the spectrum as a function of laser intensity and X-ray yield as a function of laser pulse duration, are studied.

Experimental evidence for nonlinear optical behaviour due to the spontaneous formation of wavelength-scale density modulations or gratings in suspensions of dielectric particles is presented. A collection of dielectric par- ticles pumped by a coherent radiation ®eld may simultaneously form a density grating on the scale of the radiation wavelength and a coherently backscattered radiation ®eld. The particle density grating is generated as a result of a periodic ponderomotive potential formed by the interference of the pump and back- scattered ®elds. The experiment used a water suspension of latex microspheres (radiuso56nm) pumped by a green CW laser (532nm, power 45W). A theoretical model of collective scattering of light from dielectric particles has been extended to include the eA ects of viscous and Brownian forces on the particles. This model predicts a small degree of particle bunching from which coherent backscattering of the pump occurs. The results of the theoretical model compare favourably with the experimental evidence. The relation between the results presented here and the phenomenon of Collective Rayleigh Scattering (CRS) is discussed.

An investigation is taking place into a new classical scattering phenomenon called 'collective Rayleigh scattering'. A collection of dielectric particles pumped by a laser radiation field may form a strong density grating on the scale of the radiation wavelength. The particles then coherently scatter the incident radiation. Current theoretical research is confined to collective Rayleigh scattering from particles small compared with the radiation wavelength, for which there are many possible applications in the field of nonlinear optics. However, by considering larger Mie particles, it can be seen that there are also potential applications in the areas of optical particle characterization and discrimination. This paper outlines the theoretical framework of CRS and the first observations from preliminary experiments utilizing a standing-wave gradient force trap.

A general description of electro-optic detection including non-collinear phase matching and finite transverse beam profiles is presented. It is shown theoretically and experimentally that non-collinear phase matching in ZnTe (and similar materials) produces an angular chirp in the χ(2)- generated optical signal. Due to this, in non-collinear THz and probe arrangements such as single-shot THz measurements or through accidental misalignment, measurement of an undistorted THz signal is critically dependent on having sufficient angular acceptance in the optical probe path. The associated spatial walk-off can also preclude the phase retardation approximation used in THz-TDS. The rate of misalignment-induced chirping in commonly used ZnTe and GaP schemes is tabulated, allowing ready analysis of a detection system. © 2014 Optical Society of America.

This report describes the conceptual design of a proposed free electron laser test facility called CLARA that will be a major upgrade to the existing VELA accelerator test facility at Daresbury Laboratory in the UK. CLARA will be able to test a number of new free electron laser schemes that have been proposed but require a proof of principle experiment to confirm that they perform as predicted. The primary focus of CLARA will be on ultra short photon pulse generation which will take free electron lasers into a whole new regime, enabling a new area of photon science to emerge.

The Linac Coherent Light Source at the Stanford Linear Accelerator Center in the USA is producing coherent soft and hard X-rays at a brightness nearly ten orders of magnitude larger than synchrotron sources, heralding a new era in ultrafast science.

Determination of carrier multiplication efficiencies in colloidal quantum dots may be performed using transient absorption or time-resolved terahertz spectroscopy. We aim to find whether terahertz techniques allow these values to be determined more reliably. Initial measurements on commercial dots demonstrate the viability of the technique.

Laser driven terahertz radiation sources have been developed to enable energy modulation of relativistic electron bunches on a sub-picosecond timescale. Photoconductive and nonlinear optical generation schemes capable of providing the required > 1MV cm-1 field strengths, and longitudinal polarisation components, are discussed.

Terahertz time–domain spectral techniques are applied to the characterization of a He discharge plasma. Electro-optically sampling of the electric field of a quasi-unipolar terahertz pulse transmitted through the plasma has allowed both the real and imaginary parts of the plasma permittivity to be simultaneously measured over a large spectral range. The plasma density and the collisional frequency are determined within a 30 ps duration measurement window. An anomalously high collisional frequency has been measured.

Polarized X-ray pulses at 0.6 A have been generated via head-on collision of a laser pulse from the high-field laser facility at Daresbury with a 30 MeV electron bunch in the ALICE energy recovery linear accelerator. The angular distribution of the backscattered X rays was obtained in single-shot using a scintillation screen. The temporal profile of the X ray yield as a function of the time delay between the laser pulse and electron bunch was measured and agreed well with that expected from the collision point dependence of the laser-electron beam longitudinal overlap.

We demonstrate the spectral upconversion of a unipolar subpicosecond terahertz (THz) pulse, where the THz pulse is the Coulomb field of a single relativistic electron bunch. The upconversion to the optical allows remotely located detection of long wavelength and nonpropagating components of the THz spectrum, as required for ultrafast electron bunch diagnostics. The upconversion of quasimonochromatic THz radiation has also been demonstrated, allowing the observation of distinct sum- and difference-frequency mixing components in the spectrum. Polarization dependence of first and second order sidebands at omega(opt) +/- omega(THz), and omega(opt) +/- 2 omega(THz), respectively, confirms the chi((2)) frequency mixing mechanism. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3449132]

Laser-plasma wakefield-based electron accelerators are expected to deliver ultrashort electron bunches with unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment. We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5 J, 45 fs, 800 nm laser and a ZnTe-based electro-optical setup, we demonstrate the duration of laser-accelerated, quasimonoenergetic electron bunches [best fit of 32 fs (FWHM) with a 90% upper confidence level of 38 fs] to be shorter than the drive laser pulse, but similar to the plasma period. © 2010 The American Physical Society.

We describe the newly created free-electron laser facility situated at the University of Strathclyde in Scotland, which will produce ultra-short pulses of high-power electromagnetic radiation in the terahertz frequency range. The FEL will be based on a 4 MeV photoinjector producing picosecond 1 nC electron pulses and driven by a frequency tripled Ti:sapphire laser thus ensuring synchronism with conventional laser based tuneable sources. A synchronised multi-terawatt Ti:sapphire laser amplifier will be used in the study of laser/plasma/electron beam interactions and as a plasma based X-ray source. A substantial user commitment has already been made in support of the programme.

Precise measurements of the temporal profile of ultrashort electron bunches are of high interest for the optimization and operation of ultraviolet and x-ray free-electron lasers. The electro-optic (EO) technique has been applied for a single-shot direct visualization of the time profile of individual electron bunches at FLASH. This paper presents a thorough description of the experimental setup and the results. An absolute calibration of the EO technique has been performed utilizing simultaneous measurements with a transverse-deflecting radio-frequency structure that transforms the longitudinal bunch charge distribution into a transverse streak. EO signals as short as 60 fs (rms) have been observed using a gallium-phosphide (GaP) crystal, which is a new record in the EO detection of single electron bunches and close to the physical limit imposed by the EO material properties. The data are in quantitative agreement with a numerical simulation of the EO detection process.

Inverse Compton scattering is a promising method to implement a high brightness, ultra-short, energy tunable X-ray source at accelerator facilities. We have developed an inverse Compton backscattering X-ray source driven by the multi-10 TW laser installed at Daresbury. Hard X-rays, with spectral peaks ranging from 15 to 30 keV, depending on the scattering geometry, will be generated through the interaction of laser pulses with electron bunches delivered by the energy recovery linac machine, initially known as energy recovery linac prototype and subsequently renamed accelerators and lasers in combined experiments. X-ray pulses containing 9 × 107 photons per pulse will be created from head-on collisions, with a pulse duration comparable to the incoming electron bunch length. For transverse collisions 8 × 106 photons per pulse will be generated, where the laser pulse transit time defines the X-ray pulse duration. The peak spectral brightness is predicted to be ~1021 photons/(s mm2 mrad2 0.1% Δλ/λ).

The longitudinal profiles of ultrashort relativistic electron bunches at the soft x-ray free-electron laser FLASH have been investigated using two single-shot detection schemes: an electro-optic (EO) detector measuring the Coulomb field of the bunch and a radio-frequency structure transforming the charge distribution into a transverse streak. A comparison permits an absolute calibration of the EO technique. EO signals as short as 60 fs (rms) have been observed, which is a new record in the EO detection of single electron bunches and close to the limit given by the EO material properties.

Inverse Compton scattering is a promising method to implement a high brightness, ultra-short, energy tunable X-ray source at accelerator facilities. We have developed an inverse Compton backscattering X-ray source driven by the multi-10 TW laser installed at Daresbury. Hard X-rays, with spectral peaks ranging from 15 to 30 keV, depending on the scattering geometry, will be generated through the interaction of laser pulses with electron bunches delivered by the energy recovery linac machine, initially known as energy recovery linac prototype and subsequently renamed accelerators and lasers in combined experiments. X-ray pulses containing 9 107 photons per pulse will be created from head-on collisions, with a pulse duration comparable to the incoming electron bunch length. For transverse collisions 8 106 photons per pulse will be generated, where the laser pulse transit time defines the X-ray pulse duration. The peak spectral brightness is predicted to be 1021 photons/(s mm2 mrad2 0.1% Dl/l).

[Abstract unavailable]

The electro-optic effect between an ultrafast optical probe pulse and an ultrashort terahertz pulse is shown to depend on the time derivatives of the product of the probe and terahertz electric fields. Application of this theory to temporally resolved single-shot terahertz detection techniques, where the electro-optic effect is temporally localized within an optical probe pulse, shows that the description presented here differs fundamentally and verifiably from that commonly used in literature.