Waveform Synthesizer-Based Tunable Attosecond Beamline

We present the attosecond beamline we are currently developing based on a parametric waveform synthesizer. This source is based on the coherent synthesis of two phase-stable pulses generated via OPA, the NIR pulse (700–1000 nm) and IR pulse (1200–2200 nm). The delay (relative phase, RP) and CEPs can be controlled to tailor the synthesized waveform. These waveforms supports sub-cycle FWHM durations, therefore can directly generate isolated attosecond pulses via high-harmonic generation (HHG)[1], as confirmed by attosecond streaking in the <100 eV region and by CEP dependence of the HHG continuum >100 eV. The central energy, bandwidth and duration of the isolated attosecond pulses can be controlled by tailoring the waveform via the RP and CEP setpoints[2]. We are currently developing a beamline for attosecond transient absorption spectroscopy. While the main waveform driving the HHG is controlled by RP and CEP set-points, to independently control its weaker replica serving as pump pulse, we exploit a pair of motorised CaF2 wedges placed in the vacuum setup. These allow us to fine tune the dispersion of the 1.7 octave wide pump waveform and to control its CEP, as shown in Fig. 1 (a). Jointly with IAPs tunable in the region of 30–400 eV, shown in Fig. 1 (b), these advances will provide unprecedented flexibility for attosecond pump-probe experiments. Moreover, when sub-cycle waveforms are used to pump via multi-photon or strong-field excitation, attosecond-pump/attosecond-probe will be achieved. To optimize detection efficiency, we have designed a new spectrometer based on a customized multi reflection zone plate[3] provided by Nano Optics Berlin GmbH.