You are wrong, son. Although we think that the laser beam is a straight line and very small, no matter how small the laser beam is, it will have its width and its area. Moreover, the laser beam is Gaussian. What is Gaussian? You will understand by looking at the picture. In fact, the laser cannot be imaged through a concave lens! Is it amazing to see my image? biutiful, the laser that we usually think travels in a straight line is really not a straight line, and because of its own coherence, he and himself will diffract, and there is a diffraction limit, which makes it impossible for this laser to become a very thin line with a certain width forever, and after passing through the lens, this divergence will be even greater. If you don't believe me, you can find a book in the university called Laser Principle, see what it says, see what the laser beam looks like, see what the laser looks like after Fourier transform through the lens, and then look at applied optics and see how the thick lens images, and everything will be understood!