2.Is the diffraction possible if laser light is replaced by ordinarylight?
Answers
Answer:
Most of what you think you know about lasers is false.
Lasers can (but aren’t necessarily) be very collimated (nearly diffraction limited) and very narrow band (quasi-monochromatic.)
Such light can be easily focused to a very tiny spot of high intensity or can travel hundreds of feet before diverging.
If a laser beam is expanded in a high quality telescope, it can be focused hundreds of kilometers away on a spot not much larger than a basketball.
Lasers are used to measure the distance to the moon, however, the spot on the moon may be a few kilometers wide. To do better we could use adaptive optics and a 3.5 meter telescope and get a spot only about 200 meters in diameter at the moon’s surface. But that’s about the limit for now. Get a 100 meter diameter telescope and we can get that spot down to less than 10 meters, about the size of a one car garage.
The thing that most people recognize is that most laser beams are collimated much better than ordinary light sources. You could collimate regular light like that, but the efficiency would be so tiny that it would be ridiculous. A laser pointer spreads at an angle of 3 to 5 arc minutes. A very high quality flashlight will spread at 5 to 10 degrees. The main reason is the the flashlight needs to be small and not waste too much light.