DOEs in Infrared Systems for Laser Welding Applications
Diffractive optical elements (DOEs) are widely used in infrared systems, especially where industrial processes are involved. This article focuses on laser welding applications and showcases unique custom solutions that provide competitive advantage to the systems using them.
Infrared laser trends
Infrared lasers, especially in the 1um wavelength region, are the workhorses of the laser material processing industry. The first industrial lasers were CO2 mid-IR lasers. These have been gradually replaced in many applications with Nd:YAG solid-state lasers, and recently fiber lasers. The rapidly increasing power and decreasing cost of multi-kW lasers is making them ubiquitous in many industrial processes such as welding, cutting, sintering and surface treatment.
This article will focus on laser welding, which is one case study for high-powered NIR laser applications.
Introduction to laser welding
Laser welding is used in a wide range of industrial applications, including automotive, aerospace, semiconductors, electronics, medical, power, defense, and others. Compared to other laser material processing applications, these processes stand out in terms of the required laser power (multi kW) and typically use IR lasers.
For many industrial applications and processes, the raw laser beam is not the optimal shape. In the field of welding, brazing, soldering, and other similar processes, shaping the laser beam into a process-specific tailored intensity distribution can offer a valuable advantage and improve process properties. Some of these shapes include:
- Seam height
- Edge smoothness of the joints
While helping avoid unfavorable effects, such as heat affected zones (HAZ), spattering, humping, and weld porosity, DOEs present a simple, cost effective, robust and easy-to-integrate solution for many of these cases.
Diffractive Optical Element Basics
Diffractive optical elements (DOEs) are flat, window-like phase elements that use micro-structures etched into the surface of the element to create a phase delay in a portion of the light, which is illuminated through the element. This process thus modifies the output beam.
A diffractive optical element design can shape the beam into almost any desired intensity profile from splitting the beam to multiple beams sharing similar characteristics as the input beam, to flat-top distributions at any desired geometrical distribution, such as ring shapes or focal shaping, and even combining multiple functionalities on the same optical element to provide custom tailored solutions.
Holo/Or was the first diffractive optical element manufacturer to apply microelectronics fabrication processes to optical elements for commercial applications back in the late 1980’s. Since then, the diffractive optical elements market grew. Today a huge variety of laser applications enjoy the benefits that DOEs can provide.
In the case of using DOEs in infrared systems, the DOEs are fabricated on a material that is transparent to the IR spectrum. This enables high transmission efficiency and eliminates absorption that can heat up the element, causing defects which will degrade its functionality. The anti-reflection (AR) coating is also of high quality to sustain the high IR power.
Customized diffractive optical elements for laser welding applications
Holo/Or offers several different fixed and adjustable DOE solutions for laser welding, including:
- Flexishaper – An innovative solution that combines two DOEs, which enables an adjustable ring-to-spot ratio of the energy from a standard fiber laser, by simply rotating of one of the DOEs against the other. This unique solution can be applied to both single mode and multimode laser systems to find the optimal working point per process.
- C-shaper – A custom diffuser shape that allows nitrogen bubbles a place to escape from the weld area. This improves the width/depth ratio, reduces oxidation and eliminates hot cracking.
- T-shaper – An optimal solution for butt-joint welding that improves post-weld annealing, reduces weld seam angle, and enhances weld strength.
- Brazing Diffuser – A combined beam splitter and diffuser that generates two leading spots and one center spot. When scanned during a brazing process, this DOE melts the wire between the two plates, while preheating and cleaning both sides of the brazed seam.
For more information, contact Holo/Or.