Increasing the Sensitivity of Carrier-Envelope-Phase Tagging in Photoemission From Solids by Single-Shot Intensity Correction

The presence of a laser-intensity-related carrier-envelope-phase (CEP) artifact in CEP-dependent non-linear photoemission experiments using a single-shot CEP tagging technique has obscured the detection of weak intrinsic CEP effects. The artifact is found to be correlated with random laser-intensity fluctuations in the experimental setup. We, therefore, remediate this issue by implementing single-shot tagging of the laser pulse energy in addition to the present CEP tagging technique in order to assign a corresponding (pulse-averaged) laser intensity to each detected photoelectron for every laser shot. After applying intensity filtering and an appropriate intensity correction, we demonstrate the capability of detecting weak CEP-dependent photoemission from a bulk tungsten surface with a modulation depth as low as approximately 1% within a measurement time of approximately 30 min at a 10-kHz repetition rate. Our approach has proven successful in increasing the sensitivity of the single-shot CEP tagging technique, which allows the studies of weak CEP effects in atoms, molecules, and solids.