The flow of current through a wire is limited to the size of the wire. Water through a pipe is limited by the size of the pipe. What about light? Is it limited in a similar way? Let's say I drill a 1,000nm hole in a piece of 1/4 inch steel. I then shine a 5mw red laser through the hole. Does the hole restrict how much light can pass through the hole at any given moment? Let's say I increase the light through the hole by adding more lasers. Will the hole slowly start to restrict light's passage. Is there a limit to how much light can "fit" through the hole at the same time? Example Experiment: I shine the laser through the hole. I then measure the light with a photo diode and let's say I get 1 volt. Now I increase the amount of light through the hole by adding another laser of the same size. Would I now see 2 volts? What if do this again? Would I see 3 volts? Would each additional laser produce the same gain as the one before it? I understand the lasers would all have to be angled toward the hole by the same amount to actually perform this test. I also understand may need to perfect the measuring device, but I think you get the point.
Light consists of photons which are boson. Bosons like to exists in the same state. So if you can manage to let one photon pass through a specific hole, then you can pass an arbitrary number of identical photons through that same hole. In other words, the size of the hole does not put any limit on the number of photons (or the amount of light) that can pass through that hole.
There are always boundary conditions that only become relevant when you scale the process. You want to see an effect with a small hole, otherwise you would simply make your hole so large that no effect occurs.
If the hole is small enough so that diffraction effects occur behind it, the metal around the hole will melt if the light intensity is high enough.