F2 Praktikum: Transient Absorption Spectroscopy

Transient Absorption Spectroscopy

Transient absorption (TA) spectroscopy is a time-resolved nonlinear optical technique that uses short laser pulses to follow fast dynamic processes in solid and liquid material systems after pulsed optical excitation. In contemporary research, TA spectroscopy is widely used to study light-induced processes in organic molecules, nanoparticles, and semiconductors to understand fast microscopic processes and to optimize the performance of optoelectronic and photocatalytic devices.

While conventional optical spectroscopy employs continuous light excitation to measure the static optical properties of matter, TA spectroscopy provides insights into dynamic processes induced by a light pulse. For instance, optically induced charge separation occurs typically on a sub-picosecond or picosecond time-scale and can initiate photochemical reactions with a much slower dynamics on a microsecond time-scale. A detailed insight into the initial electronic processes is needed for the design and optimization of functional nanomaterials and optoelectronic devices that we use in our everyday life.

In a typical TA spectroscopy experiment, the sample is excited by a short intense laser pulse, called the pump pulse. This is followed by a low-intensity laser pulse, termed the probe pulse, which is impinging onto the same spot of the sample with varying delay time. By monitoring the transmission change of the probe pulse, which is induced by the pump pulse, as a function of the delay time, the dynamics of various relaxation, recombination and reaction processes can be investigated.

The aim of this practical course is to perform an experiment to analyse the excitation of Zinc-Tetraphenylporphyrin (ZnTPP), a molecule widely used in applications such as organic-based photovoltaic devices, and the subsequent charge transfer to a fullerene (C70) using nanosecond transient absorption spectroscopy.

Contact: t.lohmueller@lmu.de and Matthias.Kestler@physik.uni-muenchen.de