Regensburg 2025 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 61: THz and MIR physics in semiconductors

HL 61.1: Talk

Friday, March 21, 2025, 10:45–11:00, H14

Multi-photon Stark spectroscopy of ultrafast THz waveforms — •Fabian Brütting, Moritz B. Heindl, and Georg Herink — Experimental Physics VIII, University of Bayreuth, Germany

Microscopic electric waveforms can be encoded into luminescence modulations through the quantum-confined Stark effect, enabling ultrafast “videography” of local electric fields up to THz frequencies. This technique, known as Quantum-probe field microscopy (QFIM), relies on the coupling of momentary electric fields with electronic transitions in colloidal quantum dots, with detection achieved via pump-probe microscopy [1].

Here, we propose two-photon absorption (TPA) as a novel probing regime for accessing the THz-driven Stark effect. Unlike conventional Stark spectroscopy, which relies on linear one-photon absorption, TPA operates under different selection rules, resulting in distinct interaction dynamics. In particular, depending on the specific transitions being probed, we observe a sign flip of the nonlinear electro-absorption contribution relative to the linear signal. Consequently, the overall electro-absorption signal is either enhanced, reduced or even inverted compared to the linear signal.

Therefore, two-photon Stark spectroscopy offers potential for improving QFIM detection sensitivity and provides a novel strategy for the ultrafast manipulation of the optical properties in low-dimensional semiconductors.

[1] Heindl, Moritz B., et al. “Ultrafast imaging of terahertz electric waveforms using quantum dots.” Light Sci. Appl. 11.1 (2022): 5.

Keywords: THz; Stark effect; quantum dots; two-photon absorption; electro-absorption