Ultrafast intense laser explosion of hardwood

We studied the interaction of 800 nm, 200 fs laser pulses with wood (oak. maple and beech) surfaces, We observed the generation of positively and negatively charged powders, Melting of wood cellulose has been observed even for single shot scanning. We also measured the relative quantity of positively and negatively charged particles and we found that it is humidity dependent. We believe, this is principally due to phase explosion together with electron migration towards the positive end of polar fragments. (C) 2002 Elsevier Science B.V. All rights reserved.