We have developed a longitudinally excited CO2 laser (wavelength: 10.6 μm) with controllable laser parameters such as a laser pulse shape. A CO2 laser is absorbed at a glass surface due to the high absorption of glass materials. CO2 laser processing is a thermal process, and thermal effects such as cracks and HAZ occur on the glass surface. Thermal effects depend on not only the laser irradiation conditions but also glass materials. There are various types of glass having different physical constants related to heat, such as the thermal expansion coefficient and the softening point. Six types of glass, namely, crown glass, soda-lime glass, borosilicate glass, low-expansion borosilicate glass, alkali-free glass and synthetic quartz glass were irradiated with various types of short CO2 laser pulses. In the conditions of this experiment, no cracks occurred in any material. The size of the HAZ depended on the glass material, while the cutting depth was independent of the glass material.
Piercing and cutting of polyimide film were investigated by our He-free CO2 laser excited by longitudinal pulsed discharge without pre-ionization. The samples were polyimide film with a thickness of 50 μm, 100 μm, 150 μm and 200 μm. The laser pulse was a short pulse with a tail and had a laser energy of 39.6 mJ, a spike pulse width of 384 ns, a tail length of 108 μs, and an energy ratio of the spike pulse to the pulse tail of 1:128 at a repetition rate of 200 Hz. The laser beam was circular flat-top shape. The laser beam was focused to a diameter of 508 μm, with a fluence per pulse of 19.4 J/cm2. The minimum total irradiation fluence required for piercing in the film with a thickness of 200 μm was 389 J/cm2. The minimum scanning speed required for cutting in the film with a thickness of 200 μm was 15 mm/s.
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