Issue Eur. Phys. J. Appl. Phys. Volume 47, Number 3, September 2009 Article Number 30702 Number of page(s) 6 Section Photonics DOI 10.1051/epjap/2009100 Published online 10 June 2009

Eur. Phys. J. Appl. Phys. 47, 30702 (2009)
DOI: 10.1051/epjap/2009100

Influence of the pulse number and fluence of a nanosecond laser on the ablation rate of metals, semiconductors and dielectrics

I. Vladoiu, M. Stafe, C. Negutu and I.M. Popescu

Physics Department, Faculty of Applied Sciences, University “Politehnica" of Bucharest, Splaiul Independentei 313, 060042 Bucharest, Romania

vladoiu@physics.pub.ro

Received: 19 November 2008 / Received in final form: 30 March 2009 / Accepted: 1st April 2009 / Published online: 10 June 2009

Abstract
We investigated the pulsed laser ablation of metallic (Al), semiconductor (Si), and wide bandgap dielectric (LiNbO₃) targets in air at normal atmospheric conditions by using 4.5 ns pulses at 532 nm wavelength. We determined the dependence of the ablation rate on the pulse number and laser fluence. The number of consecutive laser pulses hitting the target on the same area was between 5 and 40, and the laser fluence was varied in the range of 10–250 J/cm² by changing the irradiated area at the target surface. We find that the ablation rate of the three targets is approximately constant when the pulse number is smaller than 15. Further increase of the pulse number leads to a decrease of the ablation rate, the fastest decrease of the ablation rate with pulse number being observed for the dielectric target. The dependence of the ablation rate on the laser fluence indicates two different regimes. In the first regime, which is for values of the fluence smaller than the threshold value (~70 J/cm² for Al, ~90 J/cm² for Si, and ~180 J/cm² for LiNbO₃), the ablation rate increases approximately logarithmically with the fluence. In the second regime, characterized by values of the fluence greater than the threshold value, there is a steep increase of the ablation rate. This sudden jump of the ablation rate at the threshold fluence is due to the transition from normal vaporisation to phase explosion, and to the changes in the dimensionality of the plasma-plume hydrodynamics from one-dimensional to three-dimensional.

PACS
42.62.-b - Laser applications.
61.82.Bg - Metals and alloys.
61.82.Fk - Semiconductors.
61.82.Ms - Insulators.

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