Resonance effects in Brunel harmonic generation in thin film organic semiconductors

TL;DR

This study investigates how resonance effects influence Brunel harmonic generation in thin film organic semiconductors, specifically porphyrin-based films, revealing the role of electronic excitations and interband processes in enhancing harmonic signals.

Contribution

It provides the first combined experimental and theoretical analysis of resonance effects in Brunel harmonic generation in organic semiconductor thin films, highlighting the impact of specific electronic transitions.

Findings

Resonant excitation enhances the 5th harmonic generation.

Interband processes significantly contribute to harmonic generation.

Resonance effects are likely present in other organic materials.

Abstract

Organic semiconductors have attracted extensive attention due to their excellent optical and electronic properties. Here, we present an experimental and theoretical study of Brunel harmonic generation in two types of porphyrin thin films: tetraphenylporphyrin (TPP) and its organometallic complex derivative Zinc tetraphenylporphyrin (ZnTPP). Our results show that the $\pi$-$\pi^\ast$ excitation of the porphyrin ringsystem plays a major role in the harmonic generation process. We uncovered the contribution of an interband process to Brunel harmonic generation. In particular, the resonant ($S_0 \rightarrow S_2$ transition) enhanced multiphoton excitation is found to lead to an early onset of non-perturbative behavior for the 5th harmonic. Similar resonance effects are expected in Brunel harmonic generation with other organic materials.