Towards an Intrinsic Doppler Correction for X-ray Spectroscopy of Stored Ions at CRYRING@ESR

We report on a new experimental approach for the Doppler correction of X-rays emitted by heavy ions, using novel metallic magnetic calorimeter detectors which uniquely combine a high spectral resolution with a broad bandwidth acceptance. The measurement was carried out at the electron cooler of CRYRING@ESR at GSI, Darmstadt, Germany. The X-ray emission associated with the radiative recombination of cooler electrons and stored hydrogen-like uranium ions was investigated using two novel microcalorimeter detectors positioned under 0∘ and 180∘ with respect to the ion beam axis. This new experimental setup allowed the investigation of the region of the N, M → L transitions in helium-like uranium with a spectral resolution unmatched by previous studies using conventional semiconductor X-ray detectors. When assuming that the rest-frame energy of at least a few of the recorded transitions is well-known from theory or experiments, a precise measurement of the Doppler shifted line positions in the laboratory system can be used to determine the ion beam velocity using only spectral information. The spectral resolution achievable with microcalorimeter detectors should, for the first time, allow intrinsic Doppler correction to be performed for the precision X-ray spectroscopy of stored heavy ions. A comparison with data from a previous experiment at the ESR electron cooler, as well as the conventional method of conducting Doppler correction using electron cooler parameters, will be discussed

The parametric optical waveform synthesizer as a platformfor future attosecond-pump attosecond-probe experiments

Optical waveform synthesis allows for generating optical transients withdurations down to the sub-cycle timescale allowing for strong field pumping tobe confined to only one event per pulse.We present our parametric waveform synthesizer, capable of producing waveformswith durations down to 3 fs and a spectrum from 690 nm to 2200 nm, aswell as our in-situ detection method to determine their full electric field.The synthesis of the waveforms is achieved by coherently combining two fewcyclepulses produced in parallel channels based on optical parametric amplifiers.Active stabilization of the system offers us great control and long-term stabilityof the waveforms.Using these waveforms, we could show the direct generation of isolatedattosecond pulses (IAPs) with variable duration, central energy, and bandwidthreaching up to ∼400 eV.Many strong field processes studied in attosecond science are highly fieldsensitive. Therefore, knowing the precise electric fields of the waveforms used togenerate the IAPs and pump the system under investigation is paramount.We will present our pulse characterization technique based on the observationof the perturbative nonlinear response in gas. The extremely broad spectra ofour pulses lead to the overlap of different nonlinear signals. When performinga relative delay scan of the constituent pulses, fringes sensitive to the overallcarrier-envelope phase of the waveform are observed in the recorded spectrogram.From these spectrograms we can determine the entire fields of both constituentpulses and therefore the synthesized waveform up to one global sign using acustom genetic algorithm. This allows us to determine the complete set ofpossible waveforms from a single measurement and the precise temporal overlapof the two pulses.The pulse characterization is performed fully in-situ utilizing the same gastarget used for HHG and can be carried out in parallel to an attosecond experiment.This enables us to monitor the temporal overlap and thus the waveform stability during a measurement.To perform advanced pump-probe experiments the optical waveforms mustbe independently optimized for IAP generation and the strong-field pumpingof the target. We will realize this with an additional dispersion control setupinside our beamline’s pump arm. Additionally, we are investigating ways toindependently control the intensities in both arms, which requires attenuatingour multi-octave spanning spectra

Soft X-ray continua generation via HHG with sub-cycle synthesized laser fields

Isolated attosecond soft X-ray continua are presented as generated with a synthesized infrared laser field. Sub-cycle non-sinusoidal electric fields supersede the need for any gating techniques. A vast scan of multiple synthesis parameters is presented and the interplay of waveform dependent macroscopic effects for synthesized sub-cycle driving pulse are discussed

Tunable isolated attosecond pulse generation by sub-cycle synthesized waveforms

The future development of attosecond science will largely depend on the availability of better attosecond pulsesources. In particular, the current generation of laser-based attosecond sources suffers from a low photon-flux,especially in the soft X-ray region, and a limited tunability of attosecond pulse parameters, such as its centralenergy, bandwidth and consequently pulse duration, from a single source. The latter is of particular interestin order to selectively excite electronic transitions and to concentrate the photon flux in the spectral region ofinterest. Moreover, the possibility of controlling the pulse duration can elucidate its impact on the decoherencemechanisms that follow ionization[1].In our group we use tailored IR waveforms, obtained via coherent synthesis of the output pulses from differentOPA sources, to drive the generation of attosecond pulses via HHG. Due to the optical bandwidth of almost2 octaves, these IR waveforms can have FWHM durations down to a fraction of the central optical cycle,allowing to directly generate isolated attosecond pulses (IAPs) without additional gating[2]. Moreover bycontrolling two synthesis parameters, the relative phase among the two combined pulses and the overall CEP,we demonstrated the possibility to tune the central energy and the bandwidth of the IAPs as well as theirduration, in the XUV spectral region[3]. Recently we started investigating the generation of IAPs in the softX-ray region. Preliminary observations, shown in Fig.1, suggests the possibility to obtain IAPs with photonenergies up to ~450 eV. At present, measurements to explore the possibility of increasing IAP generationefficiency in the soft X-ray region by means of non-sinusoidal optical waveforms are underway.We believe that the possibility of tuning the IAP parameters over a wide range offered by waveform synthesiscould be a great stimulus for the development of increasingly sophisticated attosecond experiments

Phase-Matching Water Window Attosecond Pulses with Sub-cycle Waveforms

Water window attosecond pulses are generated in He gas using sub-cycle tailored fields delivered by a parametric waveform synthesizer. High-harmonic spectra and photon flux measurements are carried out with two driving field intensities. Signatures of transient phase matching are identified by observing a strong modulation of the energy cutoff when the relative phase among the synthesizer's constituent pulses approaches zero

Tunable isolated attosecond pulse generation by sub-cycle synthesized waveforms

The future development of attosecond science will largely depend on the availability of better attosecond pulsesources. In particular, the current generation of laser-based attosecond sources suffers from a low photon-flux,especially in the soft X-ray region, and a limited tunability of attosecond pulse parameters, such as its centralenergy, bandwidth and consequently pulse duration, from a single source. The latter is of particular interestin order to selectively excite electronic transitions and to concentrate the photon flux in the spectral region ofinterest. Moreover, the possibility of controlling the pulse duration can elucidate its impact on the decoherencemechanisms that follow ionization[1].In our group we use tailored IR waveforms, obtained via coherent synthesis of the output pulses from differentOPA sources, to drive the generation of attosecond pulses via HHG. Due to the optical bandwidth of almost2 octaves, these IR waveforms can have FWHM durations down to a fraction of the central optical cycle,allowing to directly generate isolated attosecond pulses (IAPs) without additional gating[2]. Moreover bycontrolling two synthesis parameters, the relative phase among the two combined pulses and the overall CEP,we demonstrated the possibility to tune the central energy and the bandwidth of the IAPs as well as theirduration, in the XUV spectral region[3]. Recently we started investigating the generation of IAPs in the softX-ray region. Preliminary observations, shown in Fig.1, suggests the possibility to obtain IAPs with photonenergies up to ~450 eV. At present, measurements to explore the possibility of increasing IAP generationefficiency in the soft X-ray region by means of non-sinusoidal optical waveforms are underway.We believe that the possibility of tuning the IAP parameters over a wide range offered by waveform synthesiscould be a great stimulus for the development of increasingly sophisticated attosecond experiments

Controlling water-window high-harmonic generation with sub-cycle synthesized waveforms

We present the first results concerning synthesizer-driven high-harmonic generation that reach the water-window region. This approach holds the promise of offering greater spectral tunability in the generation of isolated attosecond pulses and at the same time of achieving higher photon-flux, required for attosecondresolved soft X-ray transient absorption experiments

Water Window Attosecond Pulses driven by Sub-cycle Tailored Waveforms

Tunable high-harmonic continua in the water window spectral region are generatedin helium using sub-cycle infrared waveforms from a parametric waveform synthesizer.Yield enhancement is observed with specific driving waveforms