Crown Glass Drilling by Short-Pulse CO₂ Laser with Tunable Pulse Tail

Hole drilling in crown glass with a large thermal expansion coefficient of 94 × 10⁻⁷ /K by a longitudinally excited short-pulse CO₂ laser with a tunable laser pulse tail was investigated. The CO₂ laser produced short laser pulses with a pulse width of about 250 ns, a pulse tail with a length of 31.4 to 134.7 μs, a spike pulse to pulse tail energy ratio of 1:7 to 1:92, and a fluence per single pulse of 6.0 to 37.9 J/cm² at a repetition rate of 1 to 400 Hz. Sample cooling was not employed in the drilling process. At a repetition rate of 1 to 90 Hz, the CO₂ laser pulses produced cracks. At a repetition rate of 100 to 140 Hz, the CO₂ laser pulses occasionally produced cracks and crack-free holes. At a repetition rate of 150 to 400 Hz, the CO₂ laser pulses produced crack-free holes. Under various irradiation conditions, the hole depth and estimated hole volume per total irradiation fluence depended on the fluence per single pulse but did not depend on the laser pulse waveform or repetition rate.