Berlin 2018 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 46: Quantum dots and wires: Optical properties III

HL 46.4: Talk

Thursday, March 15, 2018, 15:45–16:00, A 151

Nonlinear modulation of PbS/CdS quantum dots observed by sideband pump-probe technique — •Mirco Kolarczik¹, Christian Ulbrich¹, Pieter Geiregat², Yunpeng Zhu², Laxmi Kishore Sagar², Akshay Singh³, Bastian Herzog¹, Alexander W. Achtstein¹, Xiaoqin Li³, Dries van Thourhout², Zeger Hens², Nina Owschimikow¹, and Ulrike Woggon¹ — ¹Technische Universität Berlin, Germany — ²Ghent University, Belgium — ³University of Texas, Austin, Texas, United States

Optimizing active materials for GBit/s and Tbit/s rates in optical telecommunications demands a characterization of the material on ultrafast timescales. Colloidal PbS/CdS quantum dots (QDs) are a promising system for nanophotonic applications in the near infrared. For characterization purposes, spin-coating of quantum dots onto silicon nitride waveguides is an easy way to integrate nanocrystals into optical fiber networks. However, the overlap of the QDs and the waveguide mode is comparatively small, posing challenges to ultrafast spectroscopy. Douple-chop pump-probe setups provide high sensitivity, but usually lack the phase-sensitivity of heterodyne detection setups. Our hybrid setup provides both: Two parallel lock-in units detect the main heterodyne band and a pump-dependent sideband. Analog signal pre-conditioning allows for the detection of amplitude modulations in the range of 10⁻⁵ and corresponding phase-shifts of few arcseconds. While the ground state lifetime of PbS/CdS QDs is on the microsecond timescale, we observe fast sub-nanosecond modulation due to Auger effects and biexciton decay for high laser repetition rates (75 MHz).