Laser micro milling is a process whereby cavities and pockets can be created in the surface of a piece of material by laser ablation. It's main benefits over photo-etching are that laser micro machining can achieve very smooth surfaces whereas photo etching can only reveal the grain pattern that is rolled into the stock.
Laser micro milling is also used to put the finishing touches on very fine though slots, slots that cannot be made accurate enough by any other method.