COPPER-VAPOR LASER DRILLING OF COPPER, IRON, AND TITANIUM FOILS IN ATMOSPHERIC-PRESSURE AIR AND ARGON

A copper vapor laser (511 and 578 nm) is used to drill submillimeter diameter holes in 0.025-0.127 mm thick foils of copper, iron, and titanium. Foils are machined in atmospheric pressure air and argon. The laser is repetitively pulsed at 10 kHz with a per pulse energy of 0.5 mJ giving an average power of 5 W at the sample surface for a pulse width of 40 ns. A p-i-n photodiode and a photomultiplier tube detector are connected to a digital-display timing circuit that records the number of incident laser pulses used to drill through the sample. The number of pulses is converted to an average drilling time and can provide an estimate for the average laser energy used to drill the hole. Typical data for all three materials with a per-pulse fluence of 0.7 J/cm2 ranged from 0.1 to 500 s to produce holes of approximately 0.3 mm diameter. Drilling times decreased in some cases by an order of magnitude when machining in air. This is attributed to the increased laser absorption of the metal-oxide layer formed in air and was especially noticeable with titanium. A continuous wave thermal model is used to compare experimental data as well as verify the thermal machining mechanism.