There are multiple methods being developed to ignite nuclear fusion for power generation, including inertial confinement fusion (ICF). This method uses high-power lasers to super-heat and implode a fuel pellet to such a point that the hydrogen isotopes within the pellet collide and combine in a burst of energy. Researchers at the Naval Research Laboratory have recently demonstrated focal zooming on the Nike laser; the world's largest krypton fluoride gas laser.
As the fuel pellet implodes, the lasers have to continue to shine on it, to ensure it continues collapsing to the point of initiating fusion. However, because the pellet is shrinking in size, some energy can be wasted by the laser dot covering an area larger than the pellet. This is where focal zooming comes in as it allows the focus of the laser to shrink and thereby follow the collapse of the pellet.
If the lasers used in an ICF system were capable of focal zooming, the researchers predict the size of the needed lasers could be 30% less than lasers without that feature. The smaller size will increase the efficiency of the system while also decreasing both construction and operating costs.
Source: Naval Research Laboratory