FRAME: femtosecond videography for atomic and molecular dynamics

Many important scientific questions in physics,chemistry and biology require effective methodologies to spectroscopically probe ultrafast intra-and inter-atomic/molecular dynamics.However,current methods that extend into the femtosecond regime are capable of only point measurements or single-snapshot visualizations and thus lack the capability to perform ultrafast spectroscopic videography of dynamic single events.Here we present a laser-probe-based method that enables two-dimensional videography at ultrafast timescales(femtosecond and shorter)of single,non-repetitive events.The method is based on superimposing a structural code onto the illumination to encrypt a single event,which is then deciphered in a post-processing step.This coding strategy enables laser probing with arbitrary wavelengths/bandwidths to collect signals with indiscriminate spectral information,thus allowing for ultrafast videography with full spectroscopic capability.To demonstrate the high temporal resolution of our method,we present videography of light propagation with record high 200 femtosecond temporal resolution.The method is widely applicable for studying a multitude of dynamical processes in physics,chemistry and biology over a wide range of time scales.Because the minimum frame separation(temporal resolution)is dictated by only the laser pulse duration,attosecondlaser technology may further increase video rates by several orders of magnitude.

Simultaneous multiple time scale imaging for kHz-MHz high-speed accelerometry

Fast transient events,such as the disintegration of liquid bodies or chemical reactions between radical species,involve various processes that may occur at different time scales.Currently,there are two alternatives for monitoring such events:burst-or high-speed imaging.Burst imaging at ultrahigh speeds(~100 MHz to THz)allows for the capture of nature's fastest processes but only for a narrowly confined period of time and at a repetition rate of~10 Hz.Monitoring long lasting,rapidly evolving transient events requires a significantly higher repetition rate,which is met by existing~kHz to 1 MHz high-speed imaging technology.However,the use of such systems eliminates the possibility to observe dynamics occurring on the sub-microsecond time scale.In this paper,we present a solution to this technological gap by combining multiplexed imaging with high-speed sensor technology,resulting in temporally resolved,high-spatial-resolution image series at two simultaneous time scales.We further demonstrate how the collection of such data opens up the tracking of rapidly evolving structures up to MHz burst rates over long durations,allowing,for the first time,to our knowledge,the extraction of acceleration fields acting upon the liquid bodies of an atomizing spray in two dimensions at k Hz frame rates.

The Space-Charge Problem in Ultrafast Diagnostics:An All-Optical Solution for Streak Cameras

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 sub-picosecond 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.