In this presentation, I will talk about femtosecond electronic and vibrational dynamics of common nitrogen defects in diamond as measured by different types of ultrafast spectroscopy techniques. In the first part I present results on the recombination dynamics of electrons that are photoexcited from single substitutional nitrogen (Ns) defects into the conduction band of diamond. Using femtosecond optical pump-Terahertz probe and optical pump-MIR probe measurements we find that the Ns defect not only acts as an electron donor, as is well known, but also as an electron acceptor. The second part deals with broadband transient absorption spectroscopy on the vibronic spectrum of the negatively-charged nitrogen-vacancy (NV-) defect. We find that vibrational relaxation within the phonon sideband occurs on timescales of ~100fs, about two orders of magnitude faster than previously reported. Furthermore, using polarization anisotropy, which is
sensitive to the electronic coherence of the two-fold degenerate electronic excited state, we infer bi-exponential and temperature-dependent dephasing dynamics with time constants between 100fs and 15ps. These dephasing dynamics are partly driven by non-adiabatic transitions at the conical intersection between the two Jahn-Teller-distorted excited states.
Ronald Ulbricht obtained his PhD in 2012 from the University of Amsterdam for his work on time-resolved Terahertz spectroscopy on semiconductors, carried out at the FOM Institute AMOLF. During postdoctoral stays at Nanyang Technological University (NTU) Singapore, Hokkaido University and University of Colorado in Boulder, he worked on transient absorption spectroscopy, picosecond photoacoustics and optical near-field spectroscopy techniques. He is currently a DFG research fellow at NTU Singapore.