| 1. |
- Jadoun, Deependra, 1998-, et al.
(författare)
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Tracking Conical Intersections with Nonlinear X-ray Raman Spectroscopy
- 2022
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Ingår i: Ultrafast Science. - : American Association for the Advancement of Science (AAAS). - 2097-0331 .- 2765-8791. ; 2022
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Tidskriftsartikel (refereegranskat)abstract
- Conical intersections are formed when 2 or more electronic states become degenerate and give rise to ultrafast nonadiabatic processes such as radiation-less decay channels and geometric phase effects. The branching of nuclear wave packets near a conical intersection creates a coherent superposition of electronic states, which carries information about the energy difference of the involved states. X-ray Raman techniques have been proposed to observe the coherent superposition of the electronic states and to monitor the evolving electronic state separation. However, these techniques rely on the coherence generated as the wave packet passes through the conical intersection, and the electronic energy gap before the wave packet passes through the conical intersection is not tracked. In this paper, we theoretically demonstrate how a nonlinear Raman detection scheme can be used to gain further insight into the nonadiabatic dynamics in the vicinity of the conical intersection. We employ a combination of a resonant visible/infrared pulse and an off-resonant x-ray Raman probe to map the electronic state separation around the conical intersection. We demonstrate that this technique can achieve high contrast and is able to selectively probe the narrow electronic state separation around the conical intersection.
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| 2. |
- Kornienko, Vassily, et al.
(författare)
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The Space-Charge Problem in Ultrafast Diagnostics : An All-Optical Solution for Streak Cameras
- 2024
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Ingår i: Ultrafast Science. - 2097-0331. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The field of ultrafast science is dependent on either ultrashort laser pulse technology or ultrafast passive detection. While there exists a plethora of sub-picosecond laser pulse solutions, streak cameras are singular in providing sub-picosecond passive imaging capabilities. Therefore, their use in fields ranging from medicine to physics is prevalent. Streak cameras attain such temporal resolutions by converting signal photons to electrons. However, the Coulomb repulsion force spreads these electrons spatiotemporally aggravating streak cameras’ temporal resolution and dynamic range—an effect that increases in severity in ultrafast applications where electrons are generated nearly instantaneously. While many electro-optical solutions have been proposed and successfully implemented, this issue remains as a challenge for all subpicosecond streak camera technology. Instead of resorting to electro-optical solutions, in this work, we present an all-optical approach based on the combination of photon tagging and spatial lock-in detection with a technique called periodic shadowing—that is directly applicable to all generations of streak cameras. We have demonstrated that this accessible all-optical solution, consisting of a single externally applied optical component, results in (a) a >3× improvement in dynamic range, (b) a 25% increase in temporal resolution, and (c) a reduction of background noise levels by a factor of 50, which, when combined, allows for a markedly improved accuracy in the measurement of ultrafast signals.
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| 3. |
- Plach, Marius, et al.
(författare)
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Spatial Aberrations in High-Order Harmonic Generation
- 2024
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Ingår i: Ultrafast Science. - 2097-0331. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the spatial characteristics of high-order harmonic radiation generated in argon and observe cross-like patterns in the far field. An analytical model describing harmonics from an astigmatic driving beam reveals that these patterns result from the order and generation position-dependent divergence of harmonics. Even small amounts of driving field astigmatism may result in cross-like patterns, coming from the superposition of individual harmonics with spatial profiles elongated in different directions. By correcting the aberrations using a deformable mirror, we show that fine-tuning the driving wavefront is essential for optimal spatial quality of the harmonics.
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