Using fiber lasers to engrave wood should be avoided. There are two main reasons you should not use a fiber laser to engrave wood:
Fire hazard: Applying heat to wood results in the obvious — a fire. Doing so when laser engraving can cause your wood to ignite, which is a very serious safety hazard. The hazard occurs when the beam travels to the wood where there is no controlled absorption due to its shorter wavelength.
Lack of control: Because of the uncontrolled absorption wood has on fiber lasers, it is nearly impossible to make marks that are even or clean. Therefore, they often turn out charred and are sometimes unidentifiable, making it impossible to create clear designs.
While fiber lasers can successfully engrave other materials, you should avoid using them to engrave wood and other organic materials.