Berlin 2008 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 14: Electric, electromechanical and optical properties II
DF 14.2: Vortrag
Donnerstag, 28. Februar 2008, 14:20–14:40, EB 407
Absorption of ultra-short laser pulses in dielectrics — •Stefan Linden and Bärbel Rethfeld — TU Kaiserslautern
If an insulator is irradiated by a laser pulse of sufficient high intensity, non-linear ionization processes lead to an increasing free-electron density in the conduction band of the insulator. Free electrons enhance the absorptivity of the initially transparent material and are responsible for the optical breakdown of dielectrics. The transient free electron density is a fundamental parameter for numerous theoretical and experimental investigations and applications.
To describe the transient electron density in the dielectric several models exist. Commonly, a simple rate equation is applied to describe the evolution of the free-electron density under laser irradiation. Though this equation is proved for nano- to picosecond time scales, it fails on ultra-short processes. Here, the electrons energy distribution has to be taken into account, for example in the frame of the multiple rate equation [1].
In this study we present an extension of the multiple rate equation, taking into account the recombination of excited electrons from the conduction band to exciton states. Such exciton recombination was experimentally found to occur within about 200 fs for the case of SiO2. We introduce the recombination time phenomenologically in the multiple rate equation and seek for an analytical asymptotic solution, giving information about the applicability of different approaches.
[1] B. Rethfeld, Phys. Rev. Lett. 92, 187401, (2004).