TEM investigations of thermal effects on material structure induced by femtosecond and nanosecond laser processing

Abstract

Holes drilled in Aluminum using nanosecond and femtosecond laser pluses are characterized by Transmission Electronic Microscopy (TEM). Hence we present a method for quantifying the dimensions of the heat affected zone (HAZ) surrounding micro-holes by analyzing the grain size evolution. Drilled samples investigations are performed after electrolytic thinning down to 100 nm. The experiments require a real time imaging system to shot close to the located thinner zone with an accuracy in the micrometers range. Thin Al samples are drilled both in nanosecond and femtosecond regimes using het same pulses number and the same Ti-Sapphire laser source. The regeneratively amplified ultra-short pulses are utilized at a low fluence regime, while the longer pulses are obtained from the regenerative amplifier without oscillator seeding. The main conclusion is that a 40 micrometers wide HAZ is induced by nanosecond pulses, whereas the femtosecond regime does not produce any TEM observable HAZ. It has to be noticed that the width of the femtosecond HAZ is roughly less than 2 micrometers , which is our observation limit.