Laser cutting with a Gaussian beam: “Da” or “Niet”?

The expression “high beam quality” used by laser physicists to describe a beam with the single lowest mode or several lower modes is commonly transferred into the laser material processing world with a new meaning - a laser beam that provides superior cutting speed and quality. Among other things, it is assumed that cutting with a Gaussian beam will result in the deepest cut, smallest heat affected zone, lowest angle of the kerf, and smoothest cut surface. The assumed superior performance of a Gaussian beam has been used as justification for the development of expensive Gaussian or near-Gaussian beam lasers. However, the superiority of Gausian beam performance has not been proven experimentally or theoretically. Experimental verification of this belief is difficult, because it requires a high level of control over the modal composition of the laser beam, that s nearly impossible to achieve in practice. Recently a transient hydrodynamic-thermal model for beam interaction area has been developed for cutting. This model is capable of predicting shape of the front part of the keyhole during laser cutting (or welding) for different conditions including: laser power, beam intensity distribution, beam translation speed, beam caustics profile, and position of the beam waist relative to the sample surface. Using this model, virtual experimentation was performed to simulate shape of the cutting front for a Gaussian and multi mode (top hat) laser beams.