Collimators are for point light sources, and the so-called point light sources we see more in life, such as match heads, old-fashioned flashlight bulbs, and laser light from energy optical fibers. For our industrial laser industry, we talk about collimators mainly for the laser light coming out of the energy transmission fiber.
The light from the energy optical fiber is a point light source with divergence angle（ θ) This parameter can generally be found. If we place this point light source on the focus of the optical fiber collimating mirror, we know that the light emitted from the focus of a focusing mirror (the collimating mirror actually uses the focusing mirror in reverse) becomes parallel light after passing through the focusing mirror. Many people ask me what the diameter of the beam coming out of a collimator is. Today, Jiatai is here to give you the answer: 2F * tag (1/2* θ)， If the divergence angle is 10 °, f = 150mm, then the beam diameter from the collimator is = 2 * 150 * tag (5 °) = 26.2466mm. This formula is of reference significance to the selection of galvanometer for optical fiber transmission galvanometer and welding machine. The following is what people in the fiber cutting machine industry want to know. After passing through the optical fiber collimating mirror, the laser enters the focusing mirror of the optical fiber cutting machine. According to the theory, the focal length of the collimating mirror ÷ the focal length of the focusing mirror=the ratio of the energy density after focusing to the previous density. For example, the focal length of the collimating mirror is 75mm, the focal length of the focusing mirror is 150mm, and 75 ÷ 150=1/2. That is to say, the area of the focused spot after passing through the focusing 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 one.
Some people ask why the energy density should be reduced. Isn't it better to concentrate energy density? There are several reasons:
First, if the focal length of the focus lens is shorter, the focal depth of the focus lens will be shallower, which will easily lead to poor cutting.
Second: The shorter the focal length is, the smaller the focus is, and the smaller the kerf is. The smaller the kerf is, it is not conducive to the fall of the molten slag cut out, resulting in incomplete cutting. Therefore, we generally try to use the focal length between 120-150mm as the focus lens of the optical fiber cutting machine. In addition, there are two reasons why we don't use a long focal length collimator. First, using a long focal length fiber collimator requires a larger lens diameter, which will lead to more trouble in mechanical design. Second, using a long focal length fiber collimator will cause sensitivity to the focus point of the fiber cutting machine when focusing. Once it deviates from the focus of the focus lens a little, it will appear imperceptible. This is why the focus of our general optical fiber cutting machine is generally 60-100mm.
Then let's talk about the beam expander. The beam expander also has the function of collimation, but the beam expander is for beams (beams with a certain divergence angle). The light from many lasers on the market is light beam, such as CO2 glass tube, CO2 RF tube, lamp pumped YAG laser, fiber laser with QBH, end pumped 355nm 532nm 1064nm laser, etc. The light from these lasers is light beam, And they are not strictly parallel light (when the beam quality M2 of a laser is 1, the light of this laser has no divergence angle, but this can only be an ideal state, which does not exist in real life. Generally, it is good if the M2 coefficient of the laser on the market reaches 1.2). Now let's talk about why the beam expander can play the role of collimation. As we all know, the beam expander can expand the beam. In professional terms, it is to expand the beam waist radius. The product of the laser beam waist radius and divergence angle is a fixed value. When the beam waist radius increases (i.e. beam expansion), the divergence angle decreases (to achieve the role of collimation). One conclusion is that after a N times beam expander, The divergence angle of the laser beam is reduced to 1/N of the original. For example, after passing a 4-fold beam expander, the divergence angle is reduced to 1/4 of the original. This is why we try to use a larger multiple of the beam expander (provided that the beam size after the beam expander does not exceed the size of the galvanometer spot).
The beam expander includes: CO2 beam expander, 532nm beam expander, 355nm beam expander, 1064nm beam expander and 650nm beam expander. The multiples are: 22.5 3 4 5 6 8 10 12 16 20 30 50 100 and so on.
The collimator includes: the collimator of the optical fiber welding machine (focal length 100 120 150 180mm); Optical fiber cutter collimating mirror: 30f100 diameter collimating mirror (two pieces combined), 28f60 diameter collimating mirror (two pieces combined), 25.4F75 diameter collimating mirror (two pieces combined), etc.