The smallest possible cut holes can generally be described as a multiple of the thickness of the material
Generally, it is usually said that the minimum cutable hole diameter is a multiple of the thickness of the material [T] which for a steel sheet up to 15mm is ...
1 x T for gas cutting
1-1.5 x T for Plasma Cutting
0.3-0.5 x T for Laser cutting
With laser cutting, however, you can create significantly smaller holes through so-called laser drilling.
Translation in progress
Drilling using laser through vaporization of material.