other factors the same, a picosecond laser would be 1000 times more powerful than a nanosecond laser, with peak bursts in the megawatts. Generally speaking, a picosecond laser is able to cut all the super-hard materials now used for tooling, while a nanosecond laser would be excellent on PCD and PCBN but limited in its applicability to the other materials. To be more specific, Schaeffer said lasers with pulse durations under about 10 picoseconds are “non-wavelength spe- cific,” while above this point you begin to see small dif- ferences in absorption in otherwise transparent materials, depending on the wavelength.


A picosecond laser can also sublimate the material, converting it directly from solid to gas, without any trans- fer of heat energy into the material. Even on PCD and PCBN, a nanosecond laser first heats and melts the ma- terial before vaporizing it, albeit on a very tiny scale. In practice such a laser typically heats an area, a plasma forms around this area, and then material evaporates.


Nanoseconds Versus Picoseconds


As Claus Dold, EWAG AG’s head of process technol- ogy explained, “You can’t cut pure diamond with a nano- second laser because it would be transparent. [EWAG is part of the United Grinding group, with its US head- quarters in Miamisburg, OH.] But if you were trying to cut MCD-Yellow, for example, there would be a 10–12% ab- sorption using 532-MHz light with a nanosecond pulse. That’s because there is nitrogen and other elements in it that can absorb the radiation. This is just enough to start the process. Once you ablate a little bit of the diamond, you graphitize it. And graphite absorbs all the radiation. So once the process starts you can cut this material. The problem with this is you get thermal damage which can cause defects to the cutting edge.” The differences are difficult to measure and there is some secrecy among the players. For example, Rollomatic (Le


Landeron, Switzerland with US headquarters in Mundelein, IL), won’t say what laser is used in their


AdvancedManufacturing.org LF13


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