| 1. |
- Maroju, P. K., et al.
(författare)
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Analysis of two-color photoelectron spectroscopy for attosecond metrology at seeded free-electron lasers
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:4
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Tidskriftsartikel (refereegranskat)abstract
- The generation of attosecond pulse trains at free-electron lasers opens new opportunities in ultrafast science, as it gives access, for the first time, to reproducible, programmable, extreme ultraviolet (XUV) waveforms with high intensity. In this work, we present a detailed analysis of the theoretical model underlying the temporal characterization of the attosecond pulse trains recently generated at the free-electron laser FERMI. In particular, the validity of the approximations used for the correlated analysis of the photoelectron spectra generated in the two-color photoionization experiments are thoroughly discussed. The ranges of validity of the assumptions, in connection with the main experimental parameters, are derived.
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| 2. |
- Kumar Maroju, Praveen, et al.
(författare)
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Attosecond pulse shaping using a seeded free-electron laser
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 578, s. 386-391
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Tidskriftsartikel (refereegranskat)abstract
- Attosecond pulses are central to the investigation of valence- and core-electron dynamics on their natural timescales. The reproducible generation and characterization of attosecond waveforms has been demonstrated so far only through the process of high-order harmonic generation. Several methods for shaping attosecond waveforms have been proposed, including the use of metallic filters, multilayer mirrors and manipulation of the driving field. However, none of these approaches allows the flexible manipulation of the temporal characteristics of the attosecond waveforms, and they suffer from the low conversion efficiency of the high-order harmonic generation process. Free-electron lasers, by contrast, deliver femtosecond, extreme-ultraviolet and X-ray pulses with energies ranging from tens of microjoules to a few millijoules. Recent experiments have shown that they can generate subfemtosecond spikes, but with temporal characteristics that change shot-to-shot. Here we report reproducible generation of high-energy (microjoule level) attosecond waveforms using a seeded free-electron laser. We demonstrate amplitude and phase manipulation of the harmonic components of an attosecond pulse train in combination with an approach for its temporal reconstruction. The results presented here open the way to performing attosecond time-resolved experiments with free-electron lasers.
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| 3. |
- Maroju, Praveen K., et al.
(författare)
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A Novel Attosecond Timing Tool for Free-Electron Laser Experiment
- 2020
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Ingår i: High Intensity Lasers and High Field Phenomena 2020. - 9781943580736
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Konferensbidrag (refereegranskat)abstract
- We demonstrate a novel timing tool for Free-Electron Lasers to determine the delay between an attosecond pulse train and infrared pulse with sub-optical-cycle resolu-. tion.
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| 4. |
- Bengtsson, S., et al.
(författare)
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Experimental observation of longer trajectories than previously observed in high-order harmonic generation
- 2023
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Ingår i: Physical Review A. - 2469-9926. ; 108:1
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Tidskriftsartikel (refereegranskat)abstract
- We experimentally observe longer than long trajectory influence in high-order harmonic generation (HHG) by varying the peak intensity of the driving laser field either through direct attenuation or by chirping the laser pulse. Using a theoretical Gaussian beam model to simulate spatial interference resulting from quantum path interference, we show that the measured interference patterns cannot be solely explained by the well-established short and long trajectories. The structure change is most prominent for the more divergent, off-axis components of the lower plateau harmonic region, affecting the direction and amplitude of the extreme ultraviolet light emitted, and is thus of importance for understanding and controlling the fundamentals of the HHG process.
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| 5. |
- Maroju, Praveen Kumar, et al.
(författare)
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Complex attosecond waveform synthesis at fel fermi
- 2021
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 11:21
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Tidskriftsartikel (refereegranskat)abstract
- Free-electron lasers (FELs) can produce radiation in the short wavelength range extending from the extreme ultraviolet (XUV) to the X-rays with a few to a few tens of femtoseconds pulse duration. These facilities have enabled significant breakthroughs in the field of atomic, molecular, and optical physics, implementing different schemes based on two-color photoionization mechanisms. In this article, we present the generation of attosecond pulse trains (APTs) at the seeded FEL FERMI using the beating of multiple phase-locked harmonics. We demonstrate the complex attosecond waveform shaping of the generated APTs, exploiting the ability to manipulate independently the amplitudes and the phases of the harmonics. The described generalized attosecond waveform synthesis technique with an arbitrary number of phase-locked harmonics will allow the generation of sub-100 as pulses with programmable electric fields.
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| 6. |
- Olofsson, A., et al.
(författare)
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Opto-optical modulator (OOM) for extreme ultraviolet pulses
- 2020. - 7
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Ingår i: Attosecond Physics. - : IOP Publishing. - 1742-6588. ; 1412
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Konferensbidrag (refereegranskat)abstract
- There is a profound, almost symbiotic relation between electrons and photons. When light interacts with matter the electrons in the material will start to move and oscillate. When a charged particle, such as an electron, oscillates it will act as a dipole and emit light. We utilize this symbiotic relation and extend the control of light to the extreme ultraviolet (XUV) region using the newly developed XUV opto-optical modulator.
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| 7. |
- Olofsson, A., et al.
(författare)
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Phase reconstruction of high-order harmonics by quantum path interference
- 2020. - 7
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Ingår i: Attosecond physics. - : IOP Publishing. - 1742-6588. ; 1412
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Konferensbidrag (refereegranskat)abstract
- We present a method to retrieve the phase of XUV light generated through high-order harmonic generation, by observing the intensity dependence of the interference pattern in the far-field. This interference pattern arises from electron trajectories in the generation process. These trajectories spend different time in the continuum and the phase of the generated light will therefore depend differently on the instantaneous intensity of the driving field. By changing the intensity of the driving field the phase of the contributing trajectories can be extracted.
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| 8. |
- Simpson, E. R., et al.
(författare)
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Probing Stark-induced nonlinear phase variation with opto-optical modulation
- 2019
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Ingår i: Physical Review A. - 2469-9926. ; 100:2
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Tidskriftsartikel (refereegranskat)abstract
- We extend the recently developed technique of opto-optical modulation (OOM) to probe state-resolved ac-Stark-induced phase variations of a coherently excited ensemble of helium atoms. In a joint experimental and theoretical study, we find that the spatial redirection of the resonant emission from the OOM process is different for the low-lying 1s2p state as compared with the higher-lying Rydberg states, and that this redirection can be controlled through the spatial characteristics of the infrared (IR) probe beam. In particular, we observe that the intensity dependence of the IR-induced Stark phase on the 1s2p emission is nonlinear, and that the phase accumulation changes sign for moderate intensities. Our results suggest that OOM, combined with precise experimental shaping of the probe beam, could allow future measurements of Stark-induced phase shifts of excited states.
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