Glass processing

Forming high-aspect-ratio holes in glass substrates is becoming more important, especially in the semiconductor field. Femtosecond lasers can form low-taper, high-aspect-ratio TGVs in glass at high quality, with low chipping, no cracking, and a smooth inner hole wall.

Femtosecond milling of glass gives high quality but limited throughput. GHz burst mode on the industrial femtosecond laser FemtoLux splits one high-energy pulse into a train of sub-pulses, and 70 pulses at a 2 GHz intra-burst rate deliver sevenfold throughput over single-pulse mode.

Conventional laser milling struggles to achieve high aspect ratio geometries, because ablation debris accumulates in the ablation area and prevents further material removal. Bottom-up milling focuses the laser beam at the bottom of the sample, so all ablation products leave through the backside and deep, taper-free geometries can be formed in glass.

A micro-lens array is fabricated with hybrid laser processing: burst mode combined with bottom-up milling. The device base is cut from a thick fused-silica plate, the lens array is ablated on its surface, and CO₂ laser polishing brings it to optical quality. The same route suits other custom micro-optical elements.

Conventional glass cutting removes material and leaves a kerf. Bessel beam scribing does not: a single femtosecond laser pass writes a line of voids inside the glass, and the part then separates mechanically or thermally. On 4.8 mm soda-lime glass, sidewall roughness stays below 0.5 µm at 80 mm/s.

Glass thinner than 0.5 mm cracks easily, and conventional cutting loads it thermally. Femtosecond pulses keep thermal accumulation low enough that thin substrates survive: borosilicate, fused silica and cover slips are cut, milled and drilled with minimal chipping and no cracking.

Femtosecond laser-induced selective etching is a two-step process: focused pulses modify the material structure, and a chemical etch then removes only the modified regions. It produces taper-free 3D features in transparent materials, with surface roughness in the hundreds of nanometers, and it works at wafer scale.