A. Jochmann

Absolute charge calibration of scintillating screens for relativistic electron detection

We report on new charge calibrations and linearity tests with high-dynamic range for eight different scintillating screens typically used for the detection of relativistic electrons from laser-plasma based acceleration schemes. The absolute charge calibration was done with picosecond electron bunches at the ELBE linear accelerator in Dresden. The lower detection limit in our setup for the most sensitive scintillating screen (KODAK Biomax MS) was 10 fC/mm(2). The screens showed a linear photon-to-charge dependency over several orders of magnitude. An onset of saturation effects starting around 10-100 pC/mm(2) was found for some of the screens. Additionally, a constant light source was employed as a luminosity reference to simplify the transfer of a one-time absolute calibration to different experimental setups.

Absolute response of Fuji imaging plate detectors to picosecond-electron bunches

The characterization of the absolute number of electrons generated by laser wakefield acceleration often relies on absolutely calibrated FUJI imaging plates (IP), although their validity in the regime of extreme peak currents is untested. Here, we present an extensive study on the dependence of the sensitivity of BAS-SR and BAS-MS IP to picosecond electron bunches of varying charge of up to 60 pC, performed at the electron accelerator ELBE, making use of about three orders of magnitude of higher peak intensity than in prior studies. We demonstrate that the response of the IPs shows no saturation effect and that the BAS-SR IP sensitivity of 0.0081 photostimulated luminescence per electron number confirms surprisingly well data from previous works. However, the use of the identical readout system and handling procedures turned out to be crucial and, if unnoticed, may be an important error source.

Linear and non-linear Thomson-scattering x-ray sources driven by conventionally and laser plasma accelerated electrons

Compact tuneable sources of ultrashort hard x-ray pulses can be realized by Thomson scattering, taking advantage of the comparatively short wavelength of a scattered laser pulse with respect to the period length of conventional undulators. Here, we present a detailed analysis and optimization of the efficiency of linear and non-linear Thomson scattering when the process is driven with relativistic laser pulses and when the conventional accelerator is replaced by a laser-plasma wakefield accelerator.

Optical free-electron lasers with Traveling-Wave Thomson-Scattering

We present a fully analytic model of an all-optical free electron laser (OFEL) undulator based on the Traveling-Wave Thomson-Scattering (TWTS) scheme. The TWTS undulator provides for sub-mm undulator wavelengths, does not require any material or plasma to generate or contain the undulator field and allows for sub-meter saturation lengths. Starting from a fully analytic description of the three-dimensional TWTS field we derive the OFEL pendulum equation for electrons in the TWTS field and discuss the constraints on laser and electron pulse parameters that have to be fulfilled for OFEL operation. We conclude in applying the TWTS OFEL to the realization of compact free electron laser sources at 13.5 nm and 0.2 nm using laser and electron sources in reach of present day technologies.

1-J white-light continuum from 100-TW laser pulses

We experimentally measured the supercontinuum generation using 3-J, 30-fs laser pulses and measured white-light generation at the level of 1 J. Such high energy is allowed by a strong contribution to the continuum by the photon bath, as compared to the self-guided filaments. This contribution due to the recently observed congestion of the filament number density in the beam profile at very high intensity also results in a wider broadening for positively chirped pulses rather than for negatively chirped ones, similar to broadening in hollow-core fibers.

High energy electron crystal spectrometer

A spectrometer has been developed to measure relativistic electrons produced in different types of plasmas, such as tokamak plasmas and laser produced plasmas. The spectrometer consists of nine Y2SiO5:Ce crystals, which are shielded by stainless steel filters. The absolute calibration of the spectrometer was performed at the superconducting electron linear accelerator Electron Linac for beams with high Brilliance and low Emittance. The spectrometer can provide information about energy distribution of electrons and their numbers for the energy range between 4 and 30 MeV. The spectrum is analyzed by means of the Monte Carlo three-dimensional GEANT4 code. An energy resolution of about 10% is achieved.

Characterization of Ytterbium-Doped Calcium Fluoride for Broadband Regenerative Pulse Amplification

DPSSL-systems combined with CPA technique are promising devices for generation of highest peak intensities. We report on investigations of Yb:CaF2 as broadband amplifying medium in a diode pumped regenerative amplifier for millijoule output.