Andrea Cavalleri

Abstract:

The dynamics of ablation from different absorbing and non-absorbing solid materials after excitation with 100 fs laser pulses were investigated. Using ultrafast time-resolved microscopy, the reflectivity of the excited surface was measured with both femtosecond time and micrometer spatial resolution. Transparent insulators ablation was found to be initiated by optical breakdown and plasma formation. A comparison of transient reflectivity data with the results of post mortem interference microscopy indicated that there is no significant removal of material without prior formation of a surface plasma. Quantitative measurements yielded threshold values of about 1013W/cm2, with little variation among different materials.

Abstract:

Time of flight (TOF) distributions of evaporated particles from the surface of GaAs were measured in order to determine its maximum temperature during femtosecond irradiation. A quadrupole mass spectrometer (QMS) provided the TOF distribution over a given particle mass after laser excitation. This article discusses the results of the study.

Abstract:

Femtosecond laser induced ablation from solid surfaces has been investigated by means of time resolved microscopy. On transparent materials ablation is initiated by dielectric breakdown and formation of a dense and hot surface plasma. Measurements of the plasma threshold yield values of a few times 10(13) W/cm(2) with little variation among different materials. This indicates that microscopic surface properties are responsible for surface breakdown. On absorbing semiconductors and metals near-threshold ablation is brought about by hydrodynamic expansion of the lasergenerated hot and pressurized matter. Upon expansion into vacuum initially metallic materials transform into a transparent state with a high refractive index. The observed behavior is related to general properties of matter in the liquid-gas coexistence regime.

Abstract:

Theoretical investigation has proposed fullerenes as precursors of a new family of carbon nanostructures: schwarzite, hollow diamonds, nanowires, etc. In order to explore new synthetic routes we have studied the laser-induced modification of fullerite. Ordered graphitic micro- and nano-structures have been produced by pulsed laser irradiation of fullerite under controlled atmosphere. Our experiments show the possibility of etching periodic mesoscopic structures from fullerite surfaces. Starting from fullerite, it is also possible to produce thin layers of a composite material formed by oriented graphitic nanofibers embedded in an amorphous matrix. (C) 1998 Elsevier Science Ltd. All rights reserved.