Attosecond pulses can be used to generate coherent superpositions of cationic electronic states in molecules through photoionisation. These can drive coherent electronic dynamics, which may decay within a few femtoseconds due to nuclear motion. In this work, we study the impact of the photoelectron on decoherence in the valence electron system of molecules following attosecond photoionisation. To this end, we include the photoelectron as a classical point charge in a quantum-classical simulation of light-induced ultrafast molecular dynamics and consider ionisation by sub-femtosecond pulses with distinct qualities. By disentangling the contributions of photoelectron and nuclei to the overall electronic decoherence, we nd that the photoelectron causes partial decoherence within the rst 50 attoseconds. This timescale is noticed to be independent of the ionising pulse. Full electronic decoherence is only seen when the spatial extension of the nuclear wave packet is considered.

Significance: Over the past decade, laser-based digital holographic microscopy (DHM), an important approach in the field of quantitative-phase imaging techniques, has become a significant label-free modality for live-cell imaging and used particularly in cellular neuroscience. However, coherent noise remains a major drawback for DHM, significantly limiting the possibility to visualize neuronal processes and precluding important studies on neuronal connectivity. Aim: The goal is to develop a DHM technique able to sharply visualize thin neuronal processes. Approach: By combining a wavelength-tunable light source with the advantages of hologram numerical reconstruction of DHM, an approach called polychromatic DHM (P-DHM), providing OPD images with drastically decreased coherent noise, was developed. Results: When applied to cultured neuronal networks with an air microscope objective (20×, 0.8 NA), P-DHM shows a coherent noise level typically corresponding to 1 nm at the single-pixel scale, in agreement with the 1∕ ffiffiffiffi N p-law, allowing to readily visualize the 1-μm-wide thin neuronal processes with a signal-to-noise ratio of ∼5. Conclusions: Therefore, P-DHM represents a very promising label-free technique to study neuronal connectivity and its development, including neurite outgrowth, elongation, and branching.

We demonstrate the measurement of whole-cell biophysical parameters with quantitative-phase digital holographic microscopy and flow assays. For different cell types, whole-cell mechanical properties and refractive index, mean cell thickness and absolute cell volume were obtained.

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