Ultrashort-pulse laser drilling: Determination of the threshold fluence for thin metal foils and bulk metals

Fenteng, Eric Agyei Owusu (author), Gregorčič, Peter (mentor)

Za nerjavno jeklo 316L in volfram v obliki tankih folij (50 µm) in debelejših vzorcev (3 mm) smo primerjali fluenco praga za ablacijo in inkubacijsko obnašanje pri obsevanju s femtosekundimi laserskimi bliski (300 fs). Fluenco praga za ablacijo in inkubacijske koeficienti so bili izmerjeni z metodo kvadrata premera (D2) pri ponavljalnih frekvencah 1 kHz, 333 kHz in 2 MHz, s številom impulzov od 1 do 1000. Folija in masivni vzorec sta dala podobne rezultate. Mejna fluenca se je zmanjševala s številom impulzov in se približala nasičenju nad 1000 impulzi. Inkubacijski koeficienti so ostali stabilni pri vseh uporabjenih ponavljalnih frekvencah. LIPSS so nastale blizu prage. Pri višjih fluencah so se površine zaradi taljenja zgladile, nato pa so zaradi fazne eksplozije postale še bolj hrapave.

• Language: Slovenian
• Keywords: femtosekundna laserska ablacija lasersko vrtanje prag za laserska ablacijo inkubacijski učinek akumulacija toplote metoda kvadrata premera (D^2) frekvenca bliskanja tanka folija
• Work type: Master's thesis/paper
• Organization: FS - Faculty of Mechanical Engineering
• Year: 2026
• PID: 20.500.12556/RUL-188814
• Publication date in RUL: 29.09.2026

Secondary language

• Language: English
• Title: Ultrashort-pulse laser drilling: Determination of the threshold fluence for thin metal foils and bulk metals

Abstract

The ablation threshold and incubation behaviour were compared for stainless steel 316L and tungsten in foil (50 µm) and bulk (3 mm) forms under femtosecond (300 fs) laser irradiation. The threshold fluence and incubation coefficients were measured using the diameter-squared (D^2) method at repetition rates of 1 kHz, 333 kHz and 2 MHz with number of pulses ranging from 1 to 1000. Foil and bulk samples gave similar results. The threshold fluence decreased with the number of pulses and showed a trend toward saturation above 1000 pulses. The incubation coefficients remained stable at all repetition rates applied. LIPSS formed near the threshold. Surfaces smoothed with melting at higher fluences and roughened further due to phase explosion.

• Keywords: femtosecond laser ablation laser drilling laser ablation threshold incubation effect heat accumulation d-squared method repetition rate thin foil