Spot Size Measurements for Ultra-Small Laser Welds

摘要

A desire to weld devices where significant feature sizes are on the order of micronsrnrequires laser spot sizes of similar dimensions. Since the very high power densitiesrntypically found in such tightly focused beams may cause abrupt welding-to-drillingrntransitions, knowledge of the focused spot sizes is essential for adequate process control.rnWhile determination of the focused beam diameter becomes more critical, it is harder orrnimpossible to measure with common beam characterization equipment at such small spotrnsizes. We sought a simple method for process control analogous to the commonly-usedrnKapton film method; however, at diameters of <50 microns, typical Kapton films arern"thick". Instead, we used glass microscope slides deposited with a sub-micron thickrncarbon film. A Nd:YAG 100 W pulsed laser with a 1.01mm intra-cavity aperture focusedrnthrough a 50mm focal length plano-convex microscope lens was used to produce spotsrndown to ～25 microns (～2.5x diffraction limit). We discuss the merits of the carbon-onglassrntechnique relative to Kapton film and CCD camera techniques.