Alexander Buck

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.

Ultra-high-contrast few-cycle pulses for multipetawatt-class laser technology.

We report the generation of few-cycle multiterawatt light pulses with a temporal contrast of 10(10), when measured as close as 2 ps to the pulses peak. Tens of picoseconds before the main pulse, the contrast value is expected to spread much beyond the measurement limit. Separate measurements of contrast improvement factors at different stages of the laser system indicate that real contrast values may reach 10(19) and 10(14), when measured 50 and 25 ps before the pulses peak, respectively. The combination of the shortest pulse duration and the highest contrast renders our system a promising front-end architecture for future multipetawatt laser facilities.

A high resolution, broad energy acceptance spectrometer for laser wakefield acceleration experiments.

Laser wakefield experiments present a unique challenge in measuring the resulting electron energy properties due to the large energy range of interest, typically several 100 MeV, and the large electron beam divergence and pointing jitter >1 mrad. In many experiments the energy resolution and accuracy are limited by the convolved transverse spot size and pointing jitter of the beam. In this paper we present an electron energy spectrometer consisting of two magnets designed specifically for laser wakefield experiments. In the primary magnet the field is produced by permanent magnets. A second optional electromagnet can be used to obtain better resolution for electron energies above 75 MeV. The spectrometer has an acceptance of 2.5-400 MeV (E(max)/E(min)>100) with a resolution of better than 1% rms for electron energies above 25 MeV. This high resolution is achieved by refocusing electrons in the energy plane and without any postprocessing image deconvolution. Finally, the spectrometer employs two complimentary detection mechanisms: (1) absolutely calibrated scintillation screens imaged by cameras outside the vacuum chamber and (2) an array of scintillating fibers coupled to a low-noise charge-coupled device.

Generation and applications of sub-5-fs multi-10-TW light pulses

We report on the development and relevant characteristics of an optical parametric synthesizer light source delivering sub-5-fs pulses with 80 mJ energy. The first applications of the system are attosecond and relativistic laser-plasma physics.

Generation of 8 fs, 125 mJ Pulses through Optical Parametric Chirped Pulse Amplification

We report generation of three-cycle, 8 fs, 125 mJ optical pulses in a noncollinear optical parametric chirped-pulse amplifier (NOPCPA). These 16 TW laser pulses are compressed to within 6% of their Fourier limit.

Sub-5-fs multi-TW optical parametric synthesizer

The endeavour of generating shorter and shorter light pulses lead to the optical parametric chirped pulse amplification (OPCPA) technique, which provides considerable broader gain bandwidth corresponding to a pulse duration of one to three optical cycles. Systems with such a short duration and multi-terawatt to petawatt power levels provide a unique tool for attosecond [1] and laser-plasma physics [2]. This way the generation of single attosecond pulses with unprecedented energy opens up the route to nonlinear X-ray science.

Pulse Cleaning of Few-Cycle OPCPA Pulses by Cross-Polarized Wave Generation

We present the successful implementation of cross-polarized wave generation into our few-cycle Terawatt laser system, Light Wave Synthesizer - 20 leading to a contrast improvement by more than four orders of magnitude.

Attosecond Slicing of an LWFA Produced Electron Beam

Recent years have seen rapid improvement in the quality of electron beams produced by wakefields in plasmas. The electron beams produced have inherently short durations and high peak current. To further shorten the pulse duration of these beams for future applications, an experiment is proposed to produce a single sub-femtosecond slice of electrons via an Inverse Free Electron Laser interaction (IFEL) with a few cycle laser pulse. The IFEL is followed by a combined function, permanent magnet quadrupole triplet chicane that both disperses the beam transversely while simultaneously focusing, allowing for efficient energy collimation to select the attosecond slice. Simulations are presented showing the expected electron slice characteristics.

Diagnostics of electron beams and plasma wave in laser-plasma accelerators

Relevant techniques for temporal characterization of laser-driven electron bunches as well as accelerating plasma waves are discussed. Emphasis is placed on a combination of two state-of-the-art approaches providing unique temporal information about laser plasma acceleration process and on its applicability to conventional lasers.

Dynamics of electron acceleration in plasmas

We report the first direct temporal observation [1] of self-injected and shock-front injected [2] laser-driven electron acceleration. The dynamics of the plasma wave and an electron bunch duration of 6 fs is obtained.