The collimator lens is for point light sources, and the so-called point light sources, we see more in our lives, such as: match head lighting, old-fashioned flashlight bulbs, and lasers coming out of energy fibers. For the industrial laser industry, the collimator lens basically refers to the laser coming out of the energy transmission fiber.
After passing through the fiber collimator lens, the laser enters the focusing mirror of the fiber cutting machine. According to theory, the focal length of the collimator lens, the focal length of the focusing lens = the ratio of the energy density after focusing to the previous density, such as: the focal length of the collimator lens is 75mm, the focal length of the focusing lens is 150mm, 75/150=1/2, that is, the area of the focused spot behind the mirror is twice as large as the area of the point light source just coming out of the energy fiber, and the energy density is 1/2 of the original.
Someone asked, why do you want to lower the energy density? Isn't it better to concentrate the energy density? There are several reasons:
First: If the focal length of the focusing lens is shorter, the depth of focus of the focusing lens is shallower, and the shallow depth of focus will easily lead to incomplete cutting.
Second: The shorter the focal length, the smaller the focus point, and the smaller the slit. Small slits are not conducive to the falling of the cut slag, resulting in impenetrable cutting. Therefore, we generally try to use the focal length between 120-150mm as the focusing lens of the fiber cutting machine.
In addition, why do we not use a long focal length collimator? Two reasons are involved here: ① The use of a long focal length fiber collimator lens requires a larger lens diameter, which will lead to more troublesome mechanical design; ② Use a long focal length fiber collimator lens will cause it to be very sensitive to the focus point of the fiber cutting machine when focusing. Once it deviates from the focus of the focusing lens a little bit, it will not cut through. This is why the focus of the fiber cleaver is generally between 60-100mm.