How does the laser pointer measure the thickness of hair?

You can measure the width of a hair. All you need is a dark room, a Laser pointer, some cardboard, some tape, and some mathematics. Of course, the most important hair. First, wrap the hair strands tightly on the toothpick/pen core in turn, at least dozens of turns, measure the total length with a ruler, and find the diameter of the strands. Secondly, place the strands of hair between two coverslips to make one Air wedge uses equal-thickness interference method to measure the thickness of hair strands. Fix the hair strand, irradiate it with a laser, record and shoot the diffraction pattern, use the principle of diffraction to measure the diameter of the hair strand, and compare the above three methods of measuring the diameter of the hair strand.