[mrterry]

Lasers gets fired at the inner surface of a cylinder (called a hohlraum). The laser heat the surface of the hohlraum which then emits x-rays. The x-rays then deposit energy on the surface of a spherical capsule (this is the "energy absorbed" number).

You start with ~2,000 kJ of laser energy, but some of that gets "backscattered" and never makes it into the hohlraum. Other energy is spent heating the walls of the cylinder. Additionally, some of the x-rays leak out of the hohlraum and do not drive the capsule implosion. After all these losses are taken into account, only about 15 kJ is absorbed in the capsule.