Monitoring Electronic Excitations in Oorganic Semiconductors with Ultrafast Optical Pump-probe Spectroscopy

Polarization, time and energy-resolved optical pump-probe spectroscopy is a well-established tool to monitor charge-carrier dynamics on ultrafast timescales. The general idea is that an optical excitation changes the linear response (“absorption”) properties of a sample which can be monitored optically, in a contactless, non-invasive fashion. Depending on the degree of complexity of the experiment, the data can identify structure-property relationships. For example, spatial resolution can reveal the role of grain boundaries from the effects of micro-structuring. Full polarization control enables insights into the role of delocalization and intermolecular charge transfer in crystalline samples.

In this presentation, Dr. Sangam Chatterjee, Professor at the Institute of Experimental Physics at Justus-Liebig-University (JLU) Gießen, will cover the basics of femtosecond-pump white-light probe spectroscopy. This includes the experimental challenges and essential control data to ensure reliable data. As an example, charge-carrier dynamics including singlet exciton fission in crystalline molecular films and their heterostructures will be discussed. This includes how pump-probe spectroscopy may be complemented by other time-resolved or structurally sensitive techniques.

Key learning objectives:

• Understand the concept of ultrafast optical pump-probe spectroscopy
• Comprehension of the technical requirements for a successful experiment and how it may be implemented with spatial, temporal, energy, and polarization resolution
• Gain awareness of the strengths and limitations compared to, e.g., time-resolved photoluminescence spectroscopy

Bio:

Dr. Sangam Chatterjee is full professor at the Institute of Experimental Physics I at Justus-Liebig-University (JLU) Gießen. Dr. Chatterjee’s research focuses on ultrafast spectroscopy of quasiparticles in condensed matter systems. Additionally, he oversees the growth facilities including Molecular Beam Epitaxy, Atomic Layer Deposition and Sputtering. Here, he and his group are actively developing ion-beam sputtering sources and equipment based on the RF ion thrusters invented at JLU over half a century ago. Dr. Chatterjee received his diploma in physics from the University of Karlsruhe, Germany (now Karlsruhe Institute of Technology) in2000. He obtained his Ph.D.in optical sciences from The University of Arizona, Tucson, USA, working on exciton formation in (Ga,In) As quantum wells. Next, he moved to Philipps-Universität Marburg, Germany, where his interests shifted to include active semiconductor materials including silicon photonics and molecular materials. He has been a full professor at JLU since 2018.