RECOIL PRESSURE AND SURFACE TEMPERATURE IN LASER DRILLING

摘要

To drill sub-millimeters holes one of the way is laserrndrilling. Laser drilling is a well-established industrialrnprocess from decades; however several fundamentalrnquestions are still unsolved about the physicalrnunderstanding of the laser matter interaction. Thernsequential description of the laser drilling process is asrnfollowing. The irradiated surface is heated byrnabsorption of laser energy. Once the surfacerntemperature is higher than the vaporization one, arnvapor flow is normal to the local surface. The recoilrnpressure generated by the evaporation exerts a force onrnthe melted surface and starts expelling the melt layerrnout of the hole by the side. A Mach shock disc appearsrnin the flow, the ejected vapor flow is then supersonic.rnThe surface goes deeper in the target. This paperrnrelates to an original way for measuring pressure andrnsurface temperature on target from the observations ofrnthe supersonic vapor flow. From these observationsrnand with the Prandtl-Meyer function applied on underexpandedrnsupersonic jet one can correlate the surfacerntemperature, the pressure on the melt layer and thernMach number on the supersonic jet. Results showrnbelow 22 MW.cm~(-2) of absorbed intensity the highestrnsurface temperature reached, is in the range of 5000K,rnwith a Mach number of 5 and a recoil pressure aboutrn150 bars.