How Does a Laser Machine Focus High-Energy Beams for Micro Welding Applications?
2026-09-04
In micro welding, the difference between a successful weld and a rejected part is measured in micrometers and milliseconds. The laser beam must be delivered with precision, focused to a spot size smaller than the feature being welded, and controlled with pulse timing that minimizes thermal damage to surrounding material. For the engineer responsible for selecting and operating a Laser Machine for micro welding applications, understanding the optical path from the laser source to the workpiece is as important as understanding the material properties being joined.
1. What Is the Optical Path from Laser Source to Workpiece?
The optical path of a Laser Machine designed for micro welding begins at the laser resonator, where the beam is generated. From there, the beam passes through a series of optical components: a beam expander to reduce divergence, a set of turning mirrors to direct the beam along the required path, a focusing lens or objective to concentrate the energy, and often a protective window to shield the optics from process debris. The focusing element is the most critical component. It determines the spot size and the depth of focus, which directly affect the weld quality. In our factory, we use a combination of focal lenses with different focal lengths to achieve the required spot size. A shorter focal length produces a smaller spot size but a shallower depth of focus. A longer focal length produces a larger spot size but a deeper depth of focus. The choice depends on the application. For micro welding of thin materials, a short focal length is preferred because it provides the highest intensity for a given laser power.
Key optical relationship: Spot size is determined by the laser wavelength, the beam quality (M² factor), and the focal length of the lens. A 1064 nm laser with an M² of 1.2 and a 100 mm focal length will produce a spot size of approximately 50 microns. The same laser with a 50 mm focal length will produce a spot size of 25 microns. This is why the choice of focusing optics is a critical engineering decision.
Shenzhen Alpha Tech Co., Ltd. designs Laser Machine units with adjustable focusing optics that allow the user to change the focal length without realigning the entire optical path. Our machines are equipped with a motorized Z axis that moves the focusing lens relative to the workpiece, enabling precise focus control during the welding process.
2. How Does Beam Quality (M²) Affect Focusability and Weld Quality?
The beam quality of a Laser Machine is quantified by the M² factor. An ideal Gaussian beam has an M² of 1.0. Real lasers have M² values between 1.0 and 2.0 for solid state lasers, and between 2.0 and 5.0 for high power fiber lasers. The higher the M², the larger the minimum achievable spot size for a given focal length. In micro welding applications, a low M² is essential because it allows the energy to be concentrated into a very small area. In our factory, we have tested Laser Machine units with different M² values on 0.5 mm thick stainless steel. A machine with an M² of 1.2 produced a weld width of 0.3 mm, while a machine with an M² of 2.5 produced a weld width of 0.6 mm at the same power setting. The table below shows the relationship between beam quality and spot size for different Laser Machine configurations.
| Laser type | Wavelength (nm) | Typical M² value | Minimum spot size (100 mm focal length) | Typical application |
| Nd:YAG solid state | 1064 | 1.0 – 1.5 | 25 – 40 microns | Medical device welding |
| Fiber laser | 1064 | 1.8 – 3.0 | 50 – 80 microns | General micro welding |
| Q-switched solid state | 532 | 1.0 – 1.3 | 20 – 35 microns | Fine electronics welding |
| CO₂ laser | 10600 | 2.0 – 4.0 | 100 – 200 microns | Not suitable for micro welding |
In a Laser Machine, beam quality is determined by the resonator design and the thermal management of the gain medium. Our factory uses a proprietary resonator design that maintains an M² below 1.3 even at high power levels. This is essential for micro welding applications where the weld width must be tightly controlled.
3. What Are the Key Pulse Parameters That Control Heat Input?
In micro welding, controlling the heat input is critical to avoiding thermal damage to adjacent components. The pulse duration, peak power, and repetition rate determine the energy delivered to the workpiece. A short pulse duration (1 to 10 milliseconds) allows the energy to be delivered faster than the thermal diffusion time of the material, resulting in a small heat affected zone. The table below shows the recommended pulse parameters for different micro welding applications.
| Application | Material thickness | Pulse duration (ms) | Peak power (kW) | Pulse energy (J) | Heat affected zone |
| Battery tab welding | 0.1 – 0.3 mm | 1 – 3 | 2 – 4 | 2 – 8 | < 0.3 mm |
| Medical device sealing | 0.2 – 0.5 mm | 2 – 5 | 3 – 6 | 6 – 15 | < 0.5 mm |
| Electronic component soldering | 0.05 – 0.2 mm | 0.5 – 1.5 | 1 – 3 | 0.5 – 2 | < 0.1 mm |
| Sensor housing sealing | 0.3 – 0.8 mm | 3 – 8 | 4 – 8 | 12 – 30 | < 0.6 mm |
The Laser Machine must be capable of precisely controlling these parameters. In our factory, we use a real time pulse control system that monitors the pulse shape and adjusts the laser power during the pulse to maintain constant energy delivery. This system reduces the variation in weld penetration from pulse to pulse. Shenzhen Alpha Tech Co., Ltd. integrates this control system into all of our Laser Machine units designed for micro welding.
4. How Does the Focusing System Maintain Stability During Production?
The focusing system of a Laser Machine must maintain its alignment through thermal drift, vibration, and environmental changes. In a production environment, the focusing lens can heat up due to backscattered light, causing the focal length to change. This changes the spot size and the position of the focus relative to the workpiece. Our factory uses a water cooled lens mount that maintains the lens temperature within ±2°C, regardless of the ambient temperature. We also use a beam profiler that monitors the spot size during production and adjusts the focal position if it drifts. This level of stability is essential for micro welding applications where a 10 micron change in focus position can result in a 20 percent change in weld penetration. In our factory, we have documented that the focus position of our Laser Machine units drifts by less than 5 microns over an 8 hour shift.
Frequently Asked Questions About Laser Micro Welding
Summary for Manufacturing Engineers
The performance of a Laser Machine in micro welding applications is determined by the interaction of beam quality, focusing optics, pulse parameters, and system stability. Understanding these factors allows the engineer to select the right equipment for the application and to optimize the process for the specific material and joint geometry. The key to success is to characterize the beam, to choose the correct focusing configuration, and to monitor the process stability over time. Our factory has been manufacturing Laser Machine units for precision joining applications for over 14 years. We provide full optical characterization data with each machine, including M² measurements, spot size tests, and pulse shape analysis. This data allows engineers to qualify the machine for their specific application.
Shenzhen Alpha Tech Co., Ltd. designs and manufactures Laser Machine units for micro welding, cutting, and drilling applications. We provide a complete system, including the laser source, the optical delivery system, and the motion control platform. Each machine is tested to our quality standards before shipment.
