The 193nm Excimer laser ablates a mark on the diamond in a 'cold' process. This process does not appreciably affect the area around the mark. In the picture below one can see that the surrounding material shows little sign of thermal stress after exposure to laser energy.

With most other lasers the area of thermal stress is nearly as large as the mark itself. Having said this, the 193nm Excimer is not completely free from thermal effects. One must be careful in overlapping marks at the same point, near or on a fractured area. It is possible to initiate a crack, or enlarge a crack with excessive energy, and extended laser duration with some stones. In general, however, it takes quite a large amount of energy and a long dwell time for the 193nm Excimer to risk opening a crack in a diamond.