7 research outputs found
Attosecond Delays in X-ray Molecular Ionization
The photoelectric effect is not truly instantaneous, but exhibits attosecond
delays that can reveal complex molecular dynamics. Sub-femtosecond duration
light pulses provide the requisite tools to resolve the dynamics of
photoionization. Accordingly, the past decade has produced a large volume of
work on photoionization delays following single photon absorption of an extreme
ultraviolet (XUV) photon. However, the measurement of time-resolved core-level
photoionization remained out of reach. The required x-ray photon energies
needed for core-level photoionization were not available with attosecond
tabletop sources. We have now measured the x-ray photoemission delay of
core-level electrons, and here report unexpectedly large delays, ranging up to
700 attoseconds in NO near the oxygen K-shell threshold. These measurements
exploit attosecond soft x-ray pulses from a free-electron laser (XFEL) to scan
across the entire region near the K-shell threshold. Furthermore, we find the
delay spectrum is richly modulated, suggesting several contributions including
transient trapping of the photoelectron due to shape resonances, collisions
with the Auger-Meitner electron that is emitted in the rapid non-radiative
relaxation of the molecule, and multi-electron scattering effects. The results
demonstrate how x-ray attosecond experiments, supported by comprehensive
theoretical modelling, can unravel the complex correlated dynamics of
core-level photoionization
Experimental Demonstration of Attosecond Pump-Probe Spectroscopy with an X-ray Free-Electron Laser
Pump-probe experiments with sub-femtosecond resolution are the key to
understanding electronic dynamics in quantum systems. Here we demonstrate the
generation and control of sub-femtosecond pulse pairs from a two-colour X-ray
free-electron laser (XFEL). By measuring the delay between the two pulses with
an angular streaking diagnostic, we characterise the group velocity of the XFEL
and demonstrate control of the pulse delay down to 270 as. We demonstrate the
application of this technique to a pump-probe measurement in core-excited
para-aminophenol. These results demonstrate the ability to perform pump-probe
experiments with sub-femtosecond resolution and atomic site specificity.Comment: 55 pages, main manuscript (5 figures) + supplementary materials (25
figures), 30 figures total. Submitted to Nature Photonic
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Experimental demonstration of attosecond pump–probe spectroscopy with an X-ray free-electron laser
Pump–probe experiments with subfemtosecond resolution are the key to understanding electronic dynamics in quantum systems. Here we demonstrate the generation and control of subfemtosecond pulse pairs from a two-colour X-ray free-electron laser. By measuring the delay between the two pulses with an angular streaking diagnostic, we characterize the group velocity of the X-ray free-electron laser and show control of the pulse delay down to 270 as. We confirm the application of this technique to a pump–probe measurement in core-ionized para-aminophenol. These results reveal the ability to perform pump–probe experiments with subfemtosecond resolution and atomic site specificity
Enhancing photodynamic therapy of refractory solid cancers: Combining second-generation photosensitizers with multi-targeted liposomal delivery
Contemporary photodynamic therapy (PDT) for the last-line treatment of refractory cancers such as nasopharyngeal carcinomas, superficial recurrent urothelial carcinomas, and non-resectable extrahepatic cholangiocarcinomas yields poor clinical outcomes and may be associated with adverse events. This is mainly attributable to three factors: (1) the currently employed photosensitizers exhibit suboptimal spectral properties, (2) the route of administration is associated with unfavorable photosensitizer pharmacokinetics, and (3) the upregulation of survival pathways in tumor cells may impede cell death after PDT. Consequently, there is a strong medical need to improve PDT of these recalcitrant cancers. An increase in PDT efficacy and reduction in clinical side-effects may be achieved by encapsulating second-generation photosensitizers into liposomes that selectively target to pharmacologically important tumor locations, namely tumor cells, tumor endothelium, and tumor interstitial spaces. In addition to addressing the drawbacks of clinically approved photosensitizers, this review addresses the most relevant pharmacological aspects that dictate clinical outcome, including photosensitizer biodistribution and intracellular localization in relation to PDT efficacy, the mechanisms of PDT-induced cell death, and PDT-induced antitumor immune responses. Also, a rationale is provided for the use of second-generation photosensitizers such as diamagnetic phthalocyanines (e.g., zinc or aluminum phthalocyanine), which exhibit superior photophysical and photochemical properties, in combination with a multi-targeted liposomal photosensitizer delivery system. The rationale for this PDT platform is corroborated by preliminary experimental data and proof-of-concept studies. Finally, a summary of the different nanoparticulate photosensitizer delivery systems is provided followed by a section on phototriggered release mechanisms in the context of liposomal photosensitizer delivery systems