Integrated Calendar

First-passage processes are pervasive in the world around us, yet a general framework for understanding their response to external perturbations remains elusive. In this talk, I will present a universal linear response theory for first-passage times, showing that the response of the mean first-passage time to a rare perturbation depends only on the unperturbed mean and variance, and the mean completion time after perturbation onset. I will demonstrate how this simple, yet powerful, result offers a tool for predicting the impact of perturbations on first-passage processes across various scenarios, including non-trivial ones such neural network training. I will also demonstrate how the result can be used in reverse to infer fluctuations from mean first-passage times, opening the door for the extraction of single-molecule fluctuations from bulk (concentration) measurements.FOR THE LATEST UPDATES AND CONTENT ON SOFT MATTER AND BIOLOGICAL PHYSICS AT THE WEIZMANN, VISIT OUR WEBSITE: https://www.bio

Laser-wakefield accelerators (LWFAs) have demonstrated the ability to generate high-quality, monoenergetic electron beams. Yet, efforts to achieve higher electron energies and improved accelerator efficiency remain limited by several fundamental constraints, most notably electron dephasing and beam diffraction. One promising approach to mitigating these limitations is the use of structured light to control the on-axis propagation velocity within LWFAs. By combining the diffraction-resistant characteristics of Bessel beams with spatiotemporal pulse shaping, this method promises an improved balance of extended acceleration distances and strong accelerating gradients.In this talk, we report the first experimental observation of wakefields driven by such structured-light beams as well as the first experimental evidence of the mitigation of dephasing in electron acceleration. Spatiotemporally engineered laser pulses are focused using a specialized mirror to produce a quasi-Bessel beam, and the resulting wakefields are directly measured using femtosecond relativistic electron microscopy. Numerical simulations support the experimental observations and provide new insight into this largely unexplored regime. We experimentally demonstrate control over the on-axis propagation velocity of the wakefield and follow its evolution throughout the focal region. Furthermore, we investigate how targeted spatiotemporal modifications affect both the wakefield structure and its propagation velocity. Finally, we present the first successful acceleration of electrons using these wakefields. We compare the electron profiles obtained by wakefields traveling at different velocities, demonstrating that the faster wakefield is able to achieve a higher electron cutoff energy. By combing our data with insights from simulations, we suggest the first successful partial mitigation of dephasing with such techniques. Together, these results lay the groundwork for leveraging structured-light-based techniques to overcome dephasing limitations in LWFA systems.