ELI-ALPS Research Facilities
The ELI-ALPS facility in Szeged, Hungary will be a unique, versatile laser facility with sources spanning an extremely broad range from THz to X-rays. Femtosecond, near-infrared laser pulses, with an unprecedented combination of parameters, will drive various secondary sources resulting in terahertz (THz), mid-infrared (MIR), ultraviolet (UV), extreme ultraviolet (XUV) and X-ray radiation with various, wave length dependent, pulse durations ranging from picoseconds (10‑12 s), femtoseconds (10‑15 s) down to attoseconds (10‑18 s).
The lasers systems will initially operate with modest pulse energy and longer pulses with the secondary pulse generation and user experiments will be available in late 2017. Delivery of duty-end laser amplifier; fine tuning of secondary sources and final design parameters will be realized by 2017.
ELI-ALPS, following the construction phase (2013-2017), can be used for a number of applications related to applied research and development, innovation, as well as multi- and interdisciplinary applications including biology/biophysics, chemistry, materials science and energy research. Biological, medical, and industrial applications are envisaged due to the available unique parameter combination of compact high-brilliance photon sources. The realization of highly brilliant laser-based X-ray sources will offer some parameters comparable to large-scale third-generation synchrotron radiation sources or even fourth-generation self-amplified spontaneous emission (SASE) free-electron lasers (FELs) and thus many experiments and applications, currently running or under development at these large scale facilities, may be performed on a laboratory scale in the foreseeable future.
2. ELI-ALPS infrastructure
Fig. 2.1 shows the majority of the scientific infrastructure and equipment to be installed in the main technological building of ELI-ALPS.
ELI-ALPS will include three main laser systems and additional smaller units. A laser system consists of several optical components and other laser units mounted upon optical tables. The beam delivery is a vacuum beamline system and allows distributing the individual laser beams amongst the secondary sources and the target chambers.
Secondary light sources, if required, will be generated by passing laser pulses through the appropriate medium (gas, solid surface, or optical crystal) and the resultant secondary radiation (X-ray, deep-ultraviolet, far-infrared, THz.) in conjunction with direct laser pulses, when needed, will be used within the experimental chambers for experiments and measurements.
Table 2.1 summaries the primary (laser) and secondary (laser-driven) sources of ELI-ALPS sources. There will be:
A) PW-scale femtosecond infrared laser beams with high repetition rate
B) High repetition rate, high-brightness MIR and THz beams
C) Efficient high-harmonic generation (HHG) sources from atoms (GHHG) or surfaces (SHHG), delivering XUV and X-ray photons between 10 eV and multi-10 keV
D) Relativistic laser-electron Thomson scattering source to deliver up to 100 keV X-ray photons. Available after an intensive development phase (2015-2018)
ELI-ALPS’ unique light sources will draw significant user interest from outside the basic research/attosecond science communities. The envisioned downsizing from large scale facilities to laboratory scale (in size as well as costs) will open the door to many biological, medical and industrial applications, many of which are currently hindered by the limited accessibility of beamtime at international large-scale facilities. Furthermore, many biological and medical applications require highly specialized laboratory environment (e.g. biological safety hutches, medical patient treatment environment) or dedicated cleanroom environment (semiconductor industrial applications). This cannot be realized at traditional large-scale facilities and the ELI-ALPS site offers maximum flexibility and can incorporate these needs.
3. Primary laser sources – Overview
All three major laser sources (Fig. 4.1) will deliver pulses with extremely broad bandwidths; sub-cycle phase control of the generated fields and high repetition rates. These will be realized by optical parametric chirped pulse amplifiers (OPCPA) pumped by state of the art diode-pumped solid-state lasers (DPSSL). The SYLOS and HR lasers also include double CPA with nonlinear filtering via cross polarized wave generation, and modern methods of pulse recompression in hollow core fibers (HCF).
Two custom made auxiliary laser systems will provide the user community with the broadest possible spectral coverage. The first will work in the mid-infrared range with sub mJ level pulses at 160 kHz repetition rate whilst the other will generate Joule-class UV-VIS short pulses using excimer amplifiers and will be synchronized with the HF laser.
3.1 High repetition rate (HR) laser
A white-light continuum with an octave-spanning bandwidth is generated by the fiber-amplification of a split fs pulse from an Ytterbium-doped fiber laser oscillator. After carrier envelope phase (CEP) stabilization with a feed-forward technology at 100 kHz, the stretched pulses are fed into the first OPA stages and are pumped by fiber amplifiers derived from the second part of the oscillator beam ensuring a high level of optical synchronization between the pump and seed pulses. The second amplifier branch utilizes innoslab technology which increases the pulse energy to the mJ range. The power amplifier, to be implemented in the second stage, is pumped by thin disk lasers, resulting in a five-fold (and more) increase in pulse energy .
3.2 Single cycle (SYLOS) laser
The SYLOS laser will provide the scientific backbone of the research facility and thus an extremely robust system with extreme CEP and energy stability coupled with high level of laser command and control has been commissioned. In the first stage of implementation, 30 mJ pulses with sub-7 fs duration will be generated from cross-polarized wave generated and further amplified pulses via nonlinear pulse compression in high energy HCF. In the second implementation stage (Fig. 3.2), optical parametric amplifiers further enhance the pulse energy beyond the required 100 mJ. This assumes that developments in DPSSL technology will provides, within this timeframe, a reliable pump lasers with sub-ns pulse duration and squared beam shape. The single cycle regime will be explored by 2020.
3.3 High Field (HF) laser
The petawatt class component is designed to deliver optical pulses with a 1-3 PW peak power with parameters that combine ultra-high temporal contrast (C~1012); the shortest possible pulse duration and highest repetition rate (Fig. 4.3). The PW power arm will operate at 5-10 Hz, while the second arm has a higher repetition rate with a slight reduction in output (100 Hz, 0.5 J). The HF will be synchronized with the SYLOS system enabling joint interaction experiments. During the first implementation stage, both arms of the laser will be almost completed (shown in blue in Fig. 3.3).The OPCPA stages of the PW arm will deliver <10 fs pulses with 1 J at 10 Hz, while the compressor will be scaled to accept optical pulses with energy >60 J and bandwidth supporting sub-10 fs pulses. The final stage (shown in violet) will be accomplished in the second stage of implementation and may rely on Ti:sapphire technology, since gain narrowing in this stage has be low enough to support sub 15 fs pulses. Substantially shorter pulses can be achieved with an optical parametric duty amplifier but the parametric superfluorescence contrast and substantial level of laser command control has to be yet demonstrated for PW OPA stages.
4. Attosecond sources
The primary function of all of the laser sources is to produce extremely short (attosecond) light pulses. As the pulse length of visible laser pulses cannot be made significantly shorter than the oscillation cycle of light (~2.5 fs for most laser systems), the wavelength of the laser pulse has to be reduced by high harmonic generation (HHG). The production of a broad spectrum of high harmonics in the extreme ultraviolet spectral domain enables the generation of pulse with duration of tens to several hundreds of attoseconds..
High harmonic generation is well established with laser-atom interactions enabling the construction of standard attosecond beamlines based on laser interaction with gases (HGGH) for user experiments. High harmonic generation with solid targets (SHHG) is also planned and the features and scaling of this attosecond pulse production method is under current investigation. SHHG is expected to achieve higher photon fluxes and even soft X-ray attosecond pulses.
The various maturity levels of attosecond technology means that ELI-ALPS facility will host numerous of attosecond beamlines each optimized for each of the laser systems involved and for the needs of source development vs. user requirements. This will result in individual solutions for the laser pulse energies and repetition rates. Source development beamlines will be dedicated for the investigation and further development of the attosecond pulse generation processes, whereas user beamlines will be provided for internal and external groups for ground breaking time-resolved experiments of various atomic, molecular and solid-state systems.
4.1 GHHG attosecond beamlines
Current predictions for the ELI-ALPS GHHG source, operating at 1 kHz repetition rate, will generate isolated pulses with excellent spatial coherence, ranging from the spectral region 10-40 eV with 200 nJ/pulse and >60 asec pulse duration to 200-330 eV with 1 nJ/pulse and >6 asec pulse duration. Attosecond pulse trains typically have an order of magnitude higher pulse energy. 1nJ/pulse, ~50 asec pulses delivered at 100 kHz rep rate will provide an outstanding environment for coincidence and low cross section studies (Fig. 4.1).
The facility will provide conventional methods for GHHG based on fiber and gas jet targets and it will implement innovative sources developments to increase the photon flux and reduce the attosecond pulse durations. The beamlines are designed to allow either XUV-pump XUV-probe or MIR/IR/UV-pump/probe XUV-probe/pump experiments and will enable the study the induced ultrafast temporal evolution of biological, molecular and material target systems.
Simulations of the SHHG performance for the ALPS HF laser parameters predict pulse energies of the order of 10 mJ/pulse at <100 as pulse durations for low photon energies (20-70 eV) and 10 mJ/pulse at ~5 as for high photon energies (0.4 - 1 keV). The SHHG beamline of ELI-ALPS is the first user-oriented beamline aiming at full XUV beam characterization, including temporal, spatial and spectral characterizations. The ELI-ALPS SHHG beamline is intended to boost the understanding of the generation of high flux and ultrashort attosecond pulses especially the characterization of the fundamental processes occurring during SHHG.
4.3 Novel attosecond sources
Novel types of attosecond sources are also planned using laser irradiation of nm-thin foils for coherent Thomson scattering from ultrashort relativistic electron bunches and THz-assisted HHG sources. Source development beamlines would work at 1Hz. The nonlinear motion of electrons in relativistically intense laser pulses forms the basis for the emission. However, all electrons in a nm-thick foil can move coherently in the laser field. A well-timed counter-propagating laser pulse can be backscattered from this ultra-dense electron sheath and undergo relativistic Doppler-shift resulting in a higher frequency pulse. The electron bunch can be decoupled from the driver field by the addition of a second foil which reflects the driver but is thin enough to let the electron sheath pass before the counter-propagating pulse is reflected. The mirror-like reflection can be maximized because the driver field is “switched” off. The upscaling of recent results in ELI-ALPS suggests that the attosecond pulse parameters are expected to have photon energies <1 keV; pulse energy <1 mJ; photon flux >1012 photons and pulse duration < ~ 10 as.
4.4 Detection and measurement equipments
Fig. 4.2 shows the various versatile detectors and peripheral instrumentation will be made available to the user community. There will be double-sided (electron-ion) velocity map imaging spectrometers; reaction microscopes; XUV-non-linear interferometers; XUV-pump-XUV-probe delay stages; XUV-IR cross-correlators; high spatial resolution ion microscopes; high resolution electron, ion and photon spectrometers and other diagnostic.
5.1 Particle acceleration
ELI-ALPS will host two electron acceleration sources. One will be driven by the SYLOS 1 kHz laser source and the other will be powered by the HF 10 Hz laser system. For the 1 kHz electron accelerator beamline, 2D and 3D PIC simulations predict relativistic electron bunches with an electron energy in the range of 1-100 MeV; a peak current of around 500 A; an emittance at the accelerator output of the order of 1 π mm mrad; a bunch length of a few femtoseconds and a small relative energy spread (<10% r.m.s ). One-stage and two-stage (injection-acceleration) laser plasma acceleration schemes have been considered for the 10 Hz electron beamlines. For such schemes, scaling laws, supported by 3D PIC simulations, predict that 1-10 PW class laser beams, like the HF system of ELI-ALPS, will provide high quality quasi-monochromatic few-GeV electron beams with sub-nanocoulomb charges and relative energy spreads in the 5-10 % range.
Experimental generation of the electron accelerator beamlines in both frequencies will be based on two-chamber designs. The first vacuum chamber hosts electron generation and the second vacuum chamber (or a chain of smaller vacuum chambers) will be for detectors and diagnostics.
The 1 kHz electron acceleration source can also be used as secondary light source as it is comparable to Thomson or/and Compton backscattering sources for numerous experiments in coherent transition and diffraction radiation. A high flux of MeV gamma rays photons can be made by passing the electron beam through a suitable high mass density Bremsstrahlung source target and the 10 Hz electron accelerator beamline may suitable to use for producing intense x-ray beams, energetic Compton, betatron, or Bremsstrahlung x-ray sources.
The HF laser will also drive a laser-ion source within in a separate experimental chamber. A versatile set of detection systems will be available to monitor the properties of the generated ion beam; the electrons; plasma formation , target density, and radiation dose. ELI-ALPS is ideally positioned to explore entirely new concepts of laser-driven post-acceleration using intense THz pulses. The laser-driven ions would serve also for supporting regional researches on radio-biology and radio-medicine.
5.2 High-intensity THz sources
Pulsed THz electromagnetic radiation with extremely high peak intensities offers unique possibilities with immense scientific discovery and potential applications which are impossible to obtain by using other types of radiation. One such possible application is the manipulation of charged particles. These applications are derived from the specific degrees of freedom in matter (molecules, nanostructures, condensed matter and biomaterials) accessible by wavelength of THz radiation.
At ELI-ALPS, intense and ultra-intense THz sources (centered around 1 THZ) will be available to facilitate new applications and the user community needs. Multispectral single-shot imaging and nonlinear THz spectroscopy are current applications that requiring intense THz sources and the next generation of more intense THz pulses (multi-mJ pulse energy) with extremely strong THz fields (up to 100 MV/cm) sources available at ELI-ALPS will herald a new class of applications. These include THz-assisted attosecond pulse generation; studies of the effects of extremely high THz fields, manipulation and characterization of relativistic electron beams and the post-acceleration of proton beams generated from laser plasma accelerators. THz pulses can also be used for attosecond streaking with a large time window and some of these applications will require femtosecond synchronization with ultrashort pulses in other spectral ranges. These developments will allow new types of spectroscopic studies as well as manipulation of matter from accelerated particles over molecules to nanostructures, including the enhancement of attosecond pulse generation. The coupling of high-intensity pulsed THz radiation with the various ELI-ALPS sources, from X-ray to infrared, combined with ultrashort pulse durations will enable an unprecedented variety of structural and dynamical studies for users.
6. Support Facilities
A complex network of in-house service units will be established to support experimental and theoretical research for users and staff scientists. This will be supported by highly educated technical staff. The key requirements for all of these units is the highest quality , sufficient capacity, short delivery times, creative engineering support for design.
Optical preparation and coating laboratory will be capable of design and production of custom multilayer optics for large apertures covering different wavelength ranges from IR to X-ray. A facility for electron beam lithography and plasma etching will also be available.
Optical metrology laboratory equipped with a suite of quality assurance diagnostics. Laser interferometry will be used for substrate surface, bulk quality and optical coatings characterization. The measurement suite should include a phase-shifting interferometer for 3D wavefront topography determination; a pulsed-laser-driven interferometer for gas jets characterization; a travelling microscope for the measurement of bubble/inclusion content and coating defects; a spectrophotometer for the optical characterization of coatings; a Stylus-type profiler system; a scatter measurement device; a white-light interferometer for group delay dispersion characterization and a femtosecond damage threshold testbed with a dedicated short-pulse light source.
A state-of-the-art target fabrication laboratory enables the production of targets for demanding applications, including intense high-repetition-rate sources.
6.2 Diagnostics labs and IT support
A microscope laboratory equipped with optical microscopes, AFM/STM, SEM, and possible NMR will complement the optical metrology and target fabrication capabilities.
A computer cluster with significant computational resources is required by numerical simulations supporting for example laser-plasma experiments or multi-layer mirror development. Additional service units/teams include a chemistry laboratory, a DAQ & IT group to support users in DAQ, measurement evaluation and modelling, as well as to maintain the computer facility.
6.3.1 Mechanical workshops
Special, custom-made optomechanical and vacuum elements will be designed and manufactured in-house, with close collaboration between the scientists, laser and experimental areas technicians and workshop engineers. The workshop will have to be equipped with high-precision mechanical machines including CNC-driven lathes, small, medium-sized and large milling machines, metal bending, mechanical and laser cutting machines, a sawing machine, normal and vacuum welding equipment.
6.3.2 Electronic workshops
The manufacturing of custom-made electronic components and system integration of measurement setups, beam delivery and control will be carried out on-site by trained technicians and engineers. The electronic workshop will also undertake repairs of defect facility equipment and, in special circumstances and urgent cases, user equipment. The primary focus of ELI-ALPS is ultrafast events and thus many subcomponents, lasers and detectors requiring precision timing and custom-made electronics. The workshop will subsequently be equipped with special tools and diagnostics for the broadband frequency ranges including high-end oscilloscopes, frequency generators, frequency counters, spectrum analysers as well as tools for system integration of the laser control, interlock, safety, detection and data acquisition subsystems.