The femtosecond optical Kerr effect in molten caesium chloride

Femtosecond time-resolved measurements of the optical Kerr effect in molten caesium chloride have been made. Amplified laser pulses of 115 fs duration and 1 mu J energy were used to induce a birefringence. The transmission of a weak probe pulse of the same duration gives a value of 180 fs for the relaxation time of the induced birefringence; this value is consistent with that expected for binary ionic collisions. The magnitude of the Kerr coefficient is estimated to be approximately=3*10-22 m3 V-2 (3*10-13 esu)

Wigner defects bridge the graphite gap

We present findings on the structure, energies and behaviour of defects in irradiated graphitic carbon materials. Defect production due to high-energy nuclear radiations experienced in graphite moderators is generally associated with undesirable changes in internal energy, microstructure and physical properties—the so-called Wigner effect. On the flip side, the controlled introduction and ability to handle such defects in the electron beam is considered a desirable way to engineer the properties of carbon nanostructures. In both cases, the atomic-level details of structure and interaction are only just beginning to be understood. Here, using a model system of crystalline graphite, we show from first-principles calculations, new details in the behaviour of vacancy and interstitial defects. We identify a prominent barrier-state to energy release, reveal a surprising ability of vacancy defects to bridge the widely spaced atomic layers, and discuss physical property and microstructure changes during irradiation, including interactions with dislocations