Laser ???' Microwave ovens use a magnetron oscillator to produce a electromagnetic wave of 2,4 GHz. This frequency heats water molecules, and since most food have water in it, it will heat almost any kind of food more or less uniformelly depending of the water contents and distribution in the food.

There's still some debate about the safety of microwave ovens, not in shielding but on food changes. Since the food is heated at a molecular level, it is believed that proteins can decompose and turn to unknown compounds that may be toxic. By daily experience you have noticed for sure that some heated food behaves like rubber and it taste quite different when heated in thermal ovens.