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

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 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.