The coherent artifact in modern pulse measurements

TL;DR

This paper investigates why common ultrashort pulse measurement techniques like FROG and SPIDER often fail to accurately reveal pulse structures in unstable pulse trains, highlighting a fundamental measurement artifact.

Contribution

The study demonstrates through simulations and analysis that FROG and SPIDER can misrepresent pulse characteristics in unstable ultrashort pulses, revealing a fundamental measurement artifact.

Findings

FROG shows disagreement between measured and retrieved traces in unstable pulses

SPIDER underestimates pulse duration but retrieves spectral phase correctly

Analytical calculations confirm the measurement artifacts in both techniques

Abstract

We simulate multi-shot intensity-and-phase measurements of unstable ultrashort-pulse trains using frequency-resolved-optical-gating (FROG) and spectral phase interferometry for direct electric-field reconstruction (SPIDER). Both techniques fail to reveal the pulse structure. FROG yields the average pulse duration and suggests the instability by exhibiting disagreement between measured and retrieved traces. SPIDER under-estimates the average pulse duration but retrieves the correct average pulse spectral phase. An analytical calculation confirms this behavior.