Transient material properties during defect-assisted laser breakdown in deuterated potassium dihydrogen phosphate crystals

We investigate theoretically the transition from solid dielectric materials to warm solid density plasma during laser-induced breakdown in DKDP crystals (KD2PO4). Evidence taken from the experimentally measured wavelength dependence of the breakdown threshold suggests that the material excitation mechanisms mainly consist of a sequence of one-photon absorptions between short-lived vibronic defect states spanning the band gap with a quasi-continuum of states. The transition between excitation paths involving different number of photons yields information about the role of temperature in determining the width of the transition and corresponding threshold conduction band density prior to initiation of breakdown. This physical system is well adapted to study a plasma warming up at solid density leading to the so-called warm dense matter. (C) 2014 AIP Publishing LLC.