Title: Dielectric materials in strong laser fields: measuring and modelling ablation and transient optical properties Speaker: Kristian Wædegaard IFA Time: Thursday, March 8th, 15.15 Place: Phys. Aud. Abstract: Although you would think that the interaction between light and materials is well-understood at present, the excitation of dielectric materials by intense laser pulses is still a topic of great debate. We propose a model describing the interaction between ultra-short laser pulses and dielectrics. The model allows for a self-consistent description of the electronic excitation of the material and the light propagation. The electronic excitation is described in a multiple-rate equations model [1], and includes excitation of carriers by the laser through strong-field excitation, collisional excitation, and absorption in the plasma consisting of conduction-band electrons formed during the pulse itself. By extending the model to include light propagation, the electronic excitation throughout the dielectric material can be modeled [2]. The model is used to predict the temporal evolution of the optical properties of the material as well as the ablation (material removal) rate. The simulations based on this model show that at a certain pulse energy, ablation sets in, and just above this threshold the ablation depth increases rapidly with increasing pulse energy, but it then saturates at high pulse energies. The reflectivity of the dielectric material intially increases with the pulse energy due to the increase in carrier-density, which makes the dielectric metal-like. However, for high pulse energies the reflectivity counter-intuitively decreases again. The model is compared with single-shot experiments on well-defined single-crystal dielectric samples. The experiments reproduce the distinctive dependencies on the pulse energy of both the modeled ablation depths and the optical properties [3,4]. [1] B. Rethfeld, Phys. Rev. Lett. 92, 1187401 (2004) [2] B. H. Christensen and P. Balling, Phys. Rev. B 79, 155424 (2009) [3] M. N. Christensen et al., Appl. Phys A 101, 279 (2010) [4] K. Wædegaard and P. Balling, Appl. Phys A (submitted 2012) Jacob Sherson and Aurélien Dantan Coffee, tea and cake will be served at 11.05 ----------------------------------- Aurelien Dantan Ion Trap Group Department of Physics and Astronomy University of Aarhus Ny Munkegade, bygn. 1520 8000 Aarhus Denmark +4589423602