Ultrashort pulse or femtosecond laser materials processing is an emerging technology that potentially can produce substantial cost savings in the manufacture of a wide variety of Navy systems. A laser micromachining testbed facility utilizing two industrial laser systems, a Ti:Sapphire laser capable of producing pulses of less than 150 femtoseconds and a frequency tripled Nd:YLF laser (351 nm, approximately 50 nsec pulsewidth) has been established at the Electro Optics Center (EOC). The testbed provides the EOC with a facility for feasibility testing of laser micromachining applications and a resource for workforce training. In addition, the testbed provides a unique capability of evaluating ultrashort [150 fs, long wavelength (775 nm)] pulses versus longer pulse, short wavelength (351 nm), high photon energy pulses for micromachining applications. Comparison of processing by the femtosecond and uv solid state laser will reveal the optimal processing for an intended application where throughput, stability and quality of the process can be assessed.
The theoretical criterion defining the threshold pulse energy and beam intensity required for melt ejection is proposed. The results of numerical simulation present dependencies of the threshold pulse energy and beam intensity as functions of laser pulse duration and beam radius. The experimental verification of proposed criterion is described and the comparison of theoretical predictions and measurements is presented. The criterion is applied for simulation of laser drilling metal foil with thickness in the range 25 μm - 125 μm using laser beam with 12 μm beam radius and pulse durations 10 ns and 100 ns. The computational results are used to interpret the results of experimental study of laser drilling of 125 μm aluminum foil using a single mode beam of a XeCl laser performed at the Nederlands Centrum voor Laser Research (NCLR) and the University of Twente. Additional results on Nd:YAG spot welds in pure Ni are also presented.
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