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The problem with a single laser is, that, in order to achieve bigger working widths, it would have to be able to rotate very accurately, very fast and not shoot your crops at the same time. Especially the latter makes it impossible to use a single one.
You also dont have to “burn” the weeds. It is enough to destroy certain cells to stop them from growing.
The problem is not that you need to run a single laser, but multiple lasers in order to have some form of usable working width. Then you also need to power the cooling and the computer for the plant detection. If you build some form of small scale robot it should work with solar, but any machine that is designed to get the job done relatively quick probably won’t work.
The Problem is, that these machines are hella expensive. I heard about costs of about 1.00.000€ + support. The one that I saw also has a newer version, that is probably even more expensive. Additionally you can not even closely match the efficency of herbicides, since equipment designed to apply herbicides has a working range of up to 40m and you can drive with much higher speeds.
So even tho laser looks like a promising solution they are not even anywhere close to being able to replace pesticides. There are other options for mechanically reducing weeds that may not match the efficiency, but are economically far more viable.