Regensburg 2025 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 20: Poster Scanning Probe Microscopy: Light-Matter Interactions at the Atomic Scale
O 20.1: Poster
Montag, 17. März 2025, 18:00–20:00, P2
Generation of single cycle terahertz pulses for a THz-STM and improvement of the current measurement noise — •Paul Wiechers, Christian Lotze, Florian Faaber, Vibhuti Rai, and Katharina J. Franke — Freie Universität Berlin, Fachbereich Physik,Arnimallee 14, 14195 Berlin, Germany
Terahertz Scanning Tunneling Microscopy (THz-STM) aims to combine the atomic spatial resolution of STM with the sub-picosecond time resolution commonly achieved through optical pump-probe techniques.
We generate single-cycle terahertz pulses by optical rectification and short optical pulses of various wavelengths. Particular care is taken to minimize pointing deviations of the beams, ensuring proper focusing in the STM junction, even under varying beam delay positions.
In a THz-STM experiment, the measured quantity is the low-bandwidth tunneling current. The THz-induced part of that current, due to the low duty cycle (∼ 10−5) of the THz pulses, is very small. Thus, a thorough understanding of the limiting noise sources in the measurement is important. Here, we characterize a cryogenic low-noise ammeter and increase its prohibitively low bandwidth by more than two orders of magnitude.
Keywords: Terahertz scanning tunnelling microscopy; THz STM; THz generation; Electronic noise; Current measurement