Femtosecond laser interaction with pulsed-laser deposited carbon thin films of nanoscale thickness

Abstract

The dependence of optical, electronic and thermal penetration zones on the thickness of nanoscale layers grown on silicon wafers is reported. Tetrahedral amorphous carbon (ta-C) and amorphous carbon nitride (a-C x N y ) films were prepared by inverse pulsed laser deposition (IPLD). Single-pulse modification thresholds for femtosecond laser processing proved to be dependent on the actual film thickness below 60 nm for ta-C and 90 nm for a-C x N y . The modification behaviour was governed by multiphoton processes. An effective penetration depth of the laser radiation in a-C x N y was of ca. 110 nm in accordance with two-photon absorption. Both the emergence length of ballistic hot electrons and the heat diffusion length are negligible in these thin film materials. The lower bulk value of the threshold fluence of the a-C x N y films as compared to ta-C is mainly controlled by optical contributions due to nitrogen-related defects.

Pulsed laser ablation and incubation of nickel, iron and tungsten in liquids and air

“…where U is the energy density needed to heat, melt, and vaporize the target material, R the reflectivity, and leff is the effective depth of energy deposition [21][22][23]. In the nanosecond laser interaction with metals, leff is close to the heat diffusion length lT ≈ (τ) 0.5 , where τ is the laser pulse duration,  = /(cp) the thermal diffusivity of the material,  the thermal conductivity,  the density, and cp the heat capacity.…”