Original Date: 01/27/1997
Revision Date: 01/18/2007
Best Practice : Laser Cutting and Machining
Lawrence Livermore National Laboratory (LLNL) is developing the application of extremely short pulse lasers (pulse widths <200 femtoseconds) for high precision cutting. This technology is exclusive to LLNL. It has the advantages of extreme precision, very high cutting efficiency, and minimal heating of the part being cut. The technology consistently produces kerf widths as small as 20 micrometers through metals one-millimeter thick. There is virtually no heating of the material and no detectable heat-affected zone at the cut edges. Holes drilled with femtosecond pulses are more precise and cleaner than those drilled by conventional methods.
Femtosecond lasers can cut with no collateral damage, higher precision, and higher efficiency than is achievable with conventional lasers. This makes them very useful for drilling through hard tissues such as teeth or bone where collateral damage minimization is essential. New approaches to laser dentistry and surgery are now possible. For example, ultra-short (300 femtosecond) pulses have been used successfully to drill a hole through a one-millimeter wide bone in a human middle ear.
The desirable properties for manufacturing result from the fact that energy deposition and material removal are separated with femtosecond pulses. During the pulse, energy is deposited in a scale less than one micrometer. After the pulse, hydrodynamic expansion of the hot plasma removes material from the interaction region. Therefore, each femtosecond pulse strikes a clean surface with no interference from ejecta.
LLNL built a demonstration and development workstation which serves as a prototype for the production version. This system uses a chirped pulse amplification technique which makes it possible to achieve femtosecond lasers with high peak power. An initial short pulse from a low power commercial laser is stretched in time prior to amplification with a unique LLNL grating design. Amplification by seven orders of magnitude and recompression ultimately produces a very high energy, ultra short pulse as shown in Figure 2-4. The layout for the prototype version of the laser cutter is shown in Figure 2-5.
Figure 2-4. Chirped Pulse Amplification Technique
Figure 2-5. Laser Cutting Project Schematic
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