Laser is a single-wavelength light source with good coherence performance and is widely used in scientific research and industry. Laser optics generally refers to optical elements and devices used in the internal and external optical paths of lasers, such as laser focusing mirrors, mirrors, beam expanders, and laser cutting heads. In order to let the friends intuitively understand the concept of laser focusing and collimation.

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 energy fibers. laser. For our industrial laser industry, we talk about collimating mirrors basically for the laser from the energy transmission fiber.

The light coming out of the energy fiber is a point light source with a divergence angle (θ). This parameter can generally be found. If we place this point light source at the focal point of a fiber collimator, we know that the light emitted from the focal point of a focusing lens (the collimator actually uses the focusing lens in reverse) will change after passing through the focusing lens. Become a parallel light. Many people ask me how big the beam diameter is after passing through a collimating lens. Today I will give you the answer, which is 2F*tag (1/2*θ), if the divergence angle is 10°, Fu003d150mm, then The diameter of the beam coming out of the collimator is 2*150*tag (5°)u003d26.2466mm. This formula is of reference significance for the selection of galvanometers for welding machines that use optical fiber transmission. Continue to talk about what people in the optical fiber cutting machine industry want to know. After passing through the fiber collimator, the laser enters the focusing lens of the fiber cutting machine. According to theory, the focal length of the collimator ÷ the focal length of the focusing lens u003d the ratio of the energy density after focusing to the previous density. For example, the focal length of the collimator is 75mm, The focal length of the focusing lens is 150mm, 75÷150u003d1/2, which means that the area of u200bu200bthe focused spot after the focusing lens is twice as large as the area of u200bu200bthe point light source just coming out of the energy fiber, and the energy density is 1/2 of the original .

Someone asked, why should the energy density be reduced? Isn’t it better to concentrate the energy density? There are several reasons here:

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 not deep 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: First: Use a long focal length optical fiber collimator, which requires a larger lens diameter, which will lead to more troublesome mechanical design. Second: use The long focal length of the fiber collimator 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 focus lens a little bit, the phenomenon of impenetrability will appear. This is why the focus of our general fiber cutting machine is generally between 60-100mm.

Beam expansion

In practical applications, it is often necessary to expand the laser beam. To achieve this function, at least two lenses are required. Most laser beam expanders are designed in Galileo style and consist of a combination of a positive lens and a negative lens. Because of the low expansion coefficient, simple and compact structure, it is widely used. The beam expander can achieve a smaller focusing spot by amplifying the laser beam.

In order to minimize the phase difference, it is best to choose this plano-convex and plano-concave lens, and place them on the flat side. Using the central part of the lens can further reduce the phase difference, so choosing a larger size lens will help. This kind of beam expansion design is called Galileo beam expansion. The use of two positive focal length convex lenses can also achieve the beam expansion function, which is called Kepler beam expansion, but this design has a longer size. The BEX series of beam expanders of Nanjing Wavelength Optoelectronics has complete specifications and can also be customized according to customer needs. In addition, there are also some beam expanders with specific requirements such as high-power beam expanders, which are mainly used in 1030-1090nm fiber lasers and beam expanders. The fused silica material is used to meet high-power applications, and it is connected through the C interface. In addition to the fixed zoom beam expander, there is also a zoom beam expander that can cover from ultraviolet to infrared, and the zoom range can be customized.