Tibor Wittmann

Time-resolved reflectivity measurements on a plasma mirror with few-cycle laser pulses

We present time-resolved reflectivity measurements on a plasma mirror and demonstrate the contrast improvement of sub-10-fs pulses. Detailed characterization of the spatial peak and the average reflectivity, the spatial and temporal properties of the reflected pulses for p- and also for s-polarization are discussed. A complete third-order correlation is measured to compare the temporal structures of the pulses before and after the plasma mirror. Simulation of the hydrodynamic expansion of the plasma supports the measured pulse properties after the reflection.

Attosecond control of tunneling ionization and electron trajectories

We demonstrate the control of electron tunneling in the high-order harmonic generation process and subsequent positive-energy wavepacket propagation until recollision with the unprecedented precision of about 10 attoseconds. This is accomplished with waveforms synthesized from a few-cycle near-infrared pulse and its second harmonic. The presented attosecond control of few-cycle-driven high harmonics permits the generation of tunable isolated attosecond pulses, opening the prospects for a new class of attosecond pump–probe experiments.

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.

Next Generation Driver for Attosecond and Laser-plasma Physics

The observation and manipulation of electron dynamics in matter call for attosecond light pulses, routinely available from high-order harmonic generation driven by few-femtosecond lasers. However, the energy limitation of these lasers supports only weak sources and correspondingly linear attosecond studies. Here we report on an optical parametric synthesizer designed for nonlinear attosecond optics and relativistic laser-plasma physics. This synthesizer uniquely combines ultra-relativistic focused intensities of about 1020 W/cm2 with a pulse duration of sub-two carrier-wave cycles. The coherent combination of two sequentially amplified and complementary spectral ranges yields sub-5-fs pulses with multi-TW peak power. The application of this source allows the generation of a broad spectral continuum at 100-eV photon energy in gases as well as high-order harmonics in relativistic plasmas. Unprecedented spatio-temporal confinement of light now permits the investigation of electric-field-driven electron phenomena in the relativistic regime and ultimately the rise of next-generation intense isolated attosecond sources.

Plasma mirror with few-cycle laser pulses

In this paper, the prepulses or the pedestal is intense enough to generate preplasma, which prevents the main pulse from interacting with a steep plasma. The plasma mirror is a promising technique for improving the pulse contrast. We used a Ti:Sa laser system providing 7 fs pulses with an energy of 400/spl mu/J on the target to generate and characterize the plasma mirror. The pulses are focused inside a vacuum chamber onto a glass target, which was rotated during the experiment and was replaced every two million shots. In conclusion we present an application-ready plasma mirror technique for few-cycle pulses, which improves the pulse contrast by two orders of magnitude and provides stable and well focusable pulses over an extended period of time (approx. one hour at 1 kHz pulse repetition rate).

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.

Sub-2-cycle laser-driven wakefield electron acceleration

Summary form only given. The idea of electron acceleration by laser wakefield in plasma has been suggested [1] and proved [2] to give an accelerating gradient up to several orders of magnitude higher than conventional RF based linac. The unique property of laser plasma not only offers the opportunity to build a compact X-ray source [3] but also can be used as an electron diffraction source with high temporal resolution and brightness due to the natural property of laser plasma wave.We report on experimental results of electron acceleration with LWS-20 (Light Wave Synthesizer-20) [4], which is a sub-5 fs, 16 TW OPCPA system. LWS-20 is the worlds first multi-TW sub-2-cycle light source. Our target is a supersonic He nozzle combined with shock-front injection [5]. The nozzle gives a plateau-like density profile with gas density on the order of few times 1019 cm 3, and the shock front was generated by a razor blade put into supersonic flow. The target is designed as an energy tuneable electron source by changing injection position with the blade position. The laser pulses are focused by an f/4 off-axis parabolic mirror which generates on target peak intensity of about 1019 Wcm 2. The total charge, beam profile and divergence were detected by a scintillating screen imaged onto a CCD, while the electron spectra were measured by using a carefully calibrated permanent magnet equipped with scintillating screens as detectors.Laser plasma acceleration was achieved after optimizing the most important laser and plasma parameters such as pulse duration, energy, focusing, plasma density, shock front position, etc. In a certain range of these parameters we obtained electron beams with 2.5 Hz repetition rate. We got a few pC of charge per shot within 1/e2 of electron distribution with about 25 mrad divergence in this unique regime. Typical single shot electron spectrum shows a mono-energetic dark-current-free feature with tuneable peak energy about 8-11 MeV and about 30% energy spread as shown in Fig. 1. Such an electron source has high potential for many applications such as time-resolved electron diffraction [6] or external injection source of a cascaded electron accelerator.

Stronger seed for a multiterawatt few-cycle pulse OPCPA

Summary form only given. Optical parametric chirped pulse amplification is a unique tool for amplification of ultra-broadband pulses to highest energies. In this this paper, we implement a stronger seed source which delivers muJ -level seed pulses with excellent temporal contrast. A 1 kHz, 1 mJ Ti:sapphire amplifier is used as front-end. The output pulses of the Ti:sapphire amplifier are broadened in a hollow-core fiber (HCF) obtaining ultra-broadband pulses with 400 muJ energy. A fraction of this output (50 muJ) is used to generate the seed for a broadband OPCPA in the near infrared.