The AXSIS project (Attosecond X-ray Science: Imaging and Spectroscopy) aims to develop a THz-driven compact X-ray source for applications e.g. in chemistry and biology by using ultrafast coherent diffraction imaging and spectroscopy.The key components of AXSIS are the THz-driven electron gun and THz-driven dielectric loaded linear accelerator as well as an inverse Compton scattering scheme for the X-rays production.This paper is focused on the prototype of the THz-driven electron gun which is capable of accelerating electrons up to tens of keV.Such a gun was manufactured and tested at the test-stand at DESY.Due to variations in gun fabrication and generation of THz-fields the gun is not exactly operated at design parameters.Extended simulations have been performed to understand the experimentally observed performance of the gun.A detailed comparison between simulations and experimental measurements is presented in this paper.

We describe initial steps in the development of the technology for a THz-driven accelerator that will drive a compact attosecond X-ray light source. THz-driven structures represent a promising emerging technology for compact acceleration of sub-femtosecond electron bunches. The millimeter scale of the driving field offers a favorable compromise between conventional accelerators which are proven and reliable but large and costly, and other advanced accelerators like plasma-based or laser-driven devices where the microscopic accelerator structures make device control difficult and limit the charge payload. By contrast the THz-driven structures are large enough to be fabricated by conventional means leading to a high degree of repeatability and control, can support field gradients that are significantly higher than in conventional accelerators, promising capabilities to produce sub-femtosecond electron bunches. In addition, the strong fields in THz based devices offer potential for compact, strong-field manipulation and diagnosis of electron bunches. Our results pave the way for development of a THz-based light source for sub-femtosecond investigation of material structure.

We present first results on a THz-based electron accelerator using a novel multilayer waveguide structure to utilize strong-field single-cycle THz pulses. It allows for very efficient electron acceleration using transverselycoupled short THz-waveguides with dielectric delay sections which realize phase-matching between electrons and a single-cycle THz pulse. Proof-of-concept experiments are described demonstrating 13 keV energy gain for 57 keV electron bunches from a DC-gun, which is in good agreement with simulation.

The AXSIS (Attosecond X-ray Science: Imaging and Spectroscopy) project aims for development of a compact, fully coherent, THz-driven, attosecond X-ray source. A compact THz-driven gun was developed, produced and tested as a source of the ultra-short electron bunches required for the project. To characterize the low-energy, low-charge beam produced by such a gun tailored diagnostic devices were developed and commissioned at a test-stand chamber in CFEL (DESY). Results of the first experiments on the production and characterization of the electron beam are presented.

The potential of a linear THz accelerator technology is discussed. Theoretical and first experimental results on THz-driven guns and accelerators are presented with a focus on laser based THz generation to drive these devices.

Summary form only given. With the development of modem THz technology [1], which can provide electric fields with GV/m gradients, THz-based control and manipulation of the electron bunches has become possible. THz-driven electron acceleration, compression and streaking have attracted much attention recently [2, 3]. Here, we present a novel THz driven electron streak camera that provides sub-fs temporal resolution using a multilayer structure.

We demonstrate experimentally for the first time a ~40-µJ two-octave-wide passively carrier-envelope phase (CEP)-stable parametric front-end for seeding an ytterbium (Yb)-pump-based, few-optical-cycle, high-energy optical parametric waveform synthesizer. The system includes a CEP-stable white-light continuum and two-channel optical parametric chirped pulse amplifiers (OPCPAs) in the near- and mid-infrared spectral regions spanning altogether a two-octave-wide spectrum driven by a regenerative amplifier. The output pulses are compressed and fully characterized to demonstrate the well-behaved spectral phase of this seed source.

We demonstrate the generation of 100 GHz single-cycle pulses with up to 10 MW of peak power using optical rectification and broadband phase matching via the tilted pulse front (TPF) technique in lithium niobate. The optical driver is a cryogenically cooled Yb:YAG amplifier providing tens of mJ energy, ~5 ps long laser pulses. We obtain a high THz pulse energy up to 65 µJ with 31.6 MV/m peak electric field when focused close to its diffraction limit of 2.5 mm diameter. A high optical-to-THz energy conversion efficiency of 0.3% at 85 K is measured in agreement with numerical simulations. This source is of great interest for a broad range of applications, such as nonlinear THz field-matter interaction and charged particle acceleration for ultrafast electron diffraction and table-top X-ray sources.

A cryogenically cooled Yb:YAG amplifier with 4.7-ps laser pulses is employed to generate 100-GHz pulses in lithium niobate via optical rectification. We obtained a high efficiency ~0.05% at 300 K, close to the theoretical prediction.

We demonstrate the generation of single-cycle 0.1-THz radiation in a lithium niobate crystal using optical rectification and obtain THz output energy of 65 μJ with 31.6 MV/m peak field. This amounts to an optical-to-THz energy conversion efficiency of 0.3% at 85 K, which is in agreement with theory.

We demonstrate a front-end of an Yb-based passively CEP-stable, two-octave wide, two-channel optical parametric synthesizer driven by slightly sub-picosecond pump pulses from a multi-mJ regenerative amplifier at 1 kHz.

We obtained an optical-to-terahertz (THz) energy conversion efficiency of 0.5 cryogenically cooled temperature of 100 K pumped by amplified Ti:sapphire laser pulses with 150 fs pulse duration at 800 nm wavelength. Compared with the optimized conversion efficiency of 0.18 achieved more than 2.5 times enhancement in conversion efficiency upon cryogenically cooling the crystal due to reduction of THz absorption. Further improvements to the conversion efficiency can be made by optimizing the out-coupling of the THz radiation, transportation of pump energy and by further decreasing the THz absorption in the lithium niobate crystal.

Optical rectification with tilted pulse fronts in lithium niobate crystals is one of the most promising methods to generate terahertz (THz) radiation. In order to achieve higher optical-to-THz energy efficiency, it is necessary to cryogenically cool the crystal not only to decrease the linear phonon absorption for the generated THz wave but also to lengthen the effective interaction length between infrared pump pulses and THz waves. However, the refractive index of lithium niobate crystal at lower temperature is not the same as that at room temperature, resulting in the necessity to re-optimize or even re-build the tilted pulse front setup. Here, we performed a temperature dependent measurement of refractive index and absorption coefficient on a 6.0 mol% MgO-doped congruent lithium niobate wafer by using a THz time-domain spectrometer (THz-TDS). When the crystal temperature was decreased from 300 K to 50 K, the refractive index of the crystal in the extraordinary polarization decreased from 5.05 to 4.88 at 0.4 THz, resulting in ~1° change for the tilt angle inside the lithium niobate crystal. The angle of incidence on the grating for the tilted pulse front setup at 1030 nm with demagnification factor of -0.5 needs to be changed by 3°. The absorption coefficient decreased by 60% at 0.4 THz. These results are crucial for designing an optimum tilted pulse front setup based on lithium niobate crystals.