Hc. Liu et al., Early phase laser induced plasma diagnostics and mass removal during single-pulse laser ablation of silicon, SPECT ACT B, 54(11), 1999, pp. 1607-1624
The electron number density and temperature during the early phase (< 300 n
s) of laser-induced plasmas from silicon using a 266-nm, 3-ns Nd:YAG laser
were deduced via spectroscopic methods. These parameters were measured as a
function of delay time vs. irradiance in the range of 2-80 GW/cm(2), and c
ompared with crater volume measurements. A dramatic change in plasma charac
teristics (electron number density, temperature, and degree of ionization)
as well as a sharp increase of mass removal was observed when the irradianc
e was increased beyond a threshold of 20 GW/cm(2). Possible mechanisms such
as inverse bremsstrahlung and self-regulation were used to describe these
data in the low irradiance region. Laser self-focusing and critical tempera
ture are discussed to explain the dramatic changes after the irradiance rea
ches the threshold. (C) 1999 Elsevier Science B.V. All rights reserved.