ANALYSIS: BLUE LASERS
A bright future for blue
Jean-Michel Pelaprat, co-founder of Nuburu, discusses the benefits of materials processing using emerging high-brightness blue diode lasers
industrial laser neighbourhoods – around both 1µm and 10.6µm. The power and brightness together
For decades lasers have offered unmatched flexibility for materials processing applications, but they have been capable of producing rapid high-quality welds in only a few metals. Industrially important metals, such as gold and copper, poorly absorb the infrared wavelengths of traditional materials processing lasers. Now, high-power, high- brightness blue lasers have demonstrated the ability to produce copper welds of unprecedented quality at unmatched speed. In materials processing applications, efficiency and quality are determined by a combination of wavelength, power, and brightness. The wavelength comes into the picture because, as in Figure 1, every material demonstrates different absorption for light of different wavelengths. Aluminium, stainless steel, gold, and especially copper all absorb better in the blue than in any other visible wavelength, and more than ten times better than they absorb in the traditional
determine the energy density that can be delivered to a target material. The key here is to match the energy density to an application’s needs. The beam-parameter- product of an optical system can’t be reduced, but it can be increased, so an ideal system will produce a higher energy density than the application requires. On the other hand, making the basic system too bright doesn’t help – it’s like putting a diesel locomotive engine in a lawnmower: you’re going to need so many modifications to reduce the output that you’ll spend more than necessary and still end up with an inefficient system.
The fundamental mechanism of welding
is the transfer of thermal energy to a workpiece, which melts the target material or materials. The energy transfer locus moves on, and the melted materials mix to create a joint. If too much energy is deposited into the material, it will produce
Figure 1: metals absorb differently at different wavelengths. For example, copper absorbs blue light 13 times more efficiently than it absorbs 1µm infrared radiation
Copper absorption in blue is 13x infrared
Most other metals absorption is 2x to >100x infrared
The recent emergence of blue laser processing shows promise for copper processing applications in e-mobility
miniature explosions that eject material outside of the joint and leave holes behind. Those defects are called spatter and voids respectively, and they degrade mechanical strength and increase electrical resistance of the joint. Spatter and voids are unavoidable
consequences of welding with traditional infrared lasers because the energy required to initiate a weld is much higher than that required to sustain the weld, so the infrared laser always delivers excess energy density. The same thing is true of any laser system that’s too bright. And in welding, it’s all about
Figure 2: higher brightness leads directly to increased energy density at the workpiece. For welding, higher brightness translates into faster weld speeds, increased weld penetration depth, or a combination of both
16 LASER SYSTEMS EUROPE AUTUMN 2019
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