Changes in reflectivity of various solid materials upon irradiation with high power (1012 W/cm2) ultrashort (500 fs) KrF excimer laser pulses are reported. The excimer pulse is focused by a cylindrical lens onto a line at the sample surface while a tilted wavefront (45°) probe pulse (λ = 496 nm, 500 fs pulse length) is scanning over the ablated area. Thus the spatial distribution of the reflected probe pulse corresponding to the temporal reflectivity transient, was recorded. For polymeric and semiconductor samples the reflectivity increases with a factor of 1.5-5 compared to the original value when the excimer laser pulse impinges onto the surface. It is shown that increasing the absorption of PMMA samples with naphthalene doping leads to an increase in maximum reflectivity. In case of glass reflectivity decrease is observed. The reflectivity increase or decrease is interpreted as a competing process of formation of high density free electron gas due to fast ionization processes, which leads to higher reflectance, and expansion of the ablation plume which leads to reflectivity decrease due to light scattering processes.
|Number of pages||5|
|Publication status||Published - Jan 1 2000|
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics
- Industrial and Manufacturing Engineering