*Perspective* **Probing C60 Fullerenes from within Using Free Electron Lasers**

**Nora Berrah**

> Physics Department, University of Connecticut, Storrs, CT 06268, USA; nora.berrah@uconn.edu

**Abstract:** Fullerenes, such as C60, are ideal systems to investigate energy redistribution following substantial excitation. Ultra-short and ultra-intense free electron lasers (FELs) have allowed molecular research in a new photon energy regime. FELs have allowed the study of the response of fullerenes to X-rays, which includes femtosecond multi-photon processes, as well as time-resolved ionization and fragmentation dynamics. This perspective: (1) provides a general introduction relevant to C60 research using photon sources, (2) reports on two specific X-ray FEL-based photoionization investigations of C60, at two different FEL fluences, one static and one time-resolved, and (3) offers a brief analysis and recommendations for future research.

**Keywords:** fullerenes; C60; photoionization; fragmentation; free electron laser; femtosecond; dynamics; pump probe
