High-power lasers are used to cut and weld materials by focusing the laser beam to a very small spot. this is like using a magnifying lens to focus the sun's light to a small spot that can burn things. as an engineer, you have designed a laser cutting device in which the material to be cut is placed 7.0cm behind the lens. you have selected a high-power laser with a wavelength of 1.06 \mum. (this distance and wavelength are both very typical values.) your calculations indicate that the laser must be focused to a 7.0\mum-diameter spot in order to have sufficient power to make the cut. what is the minimum diameter of the lens you must install? express your answer with the appropriate units.