USP Laser Tools in Action

SmartCleave® Glass Cutting: One of the most successful applications of USP lasers is in filament cutting of glass, increasingly used as both structural and functional elements in smartphones and other consumer products. Mechanical methods cannot easily produce the small cutouts and tight curves these applications often need, and they cannot cut chemically strengthened glass used in touchscreens.

In the SmartCleave process, the high peak intensity created by a focused USP laser produces self-focusing of the beam due to the nonlinear Kerr optical effect. This self-focusing further increases power density, until, at a certain threshold, a low-density plasma is created in the material. This plasma lowers the material refractive index in the center of the beam path and causes the beam to defocus. If the beam focusing optics are properly configured, this focusing/defocusing effect can be balanced to repeat periodically and form a stable filament which extends over several millimeters in depth through an optically transparent material. In order to achieve a continuous cut, these laser-generated filaments are produced close to each other by a relative movement of the work piece with respect to the laser beam. The typical filament diameter is in the range of 0.5 μm to 1 μm, enabling very high precision cutting.

Figure 3. Microscope edge view of 20 μm of polyimide on 0.5 mm glass, cut with a femtosecond laser with 40 watts of average power and a pulse width ~350 fs.

In the case of strengthened glass, SmartCleave with a ps laser is sufficient to separate the glass in a single step with high edge quality that requires no postprocessing. Moreover, speed is as high as 2000 mm/s depending on glass thickness. For conventional glass, a localized thermal shock is applied by closely following the USP laser beam with a jet of cold air, or sometimes a focused infrared (CO2) laser. Again, the edges exhibit no microcracking and need no grinding, and there is no residual edge stress. This is critical, because even when force is applied to the center of a glass panel, any break usually initiates at the edge.

The new generation of fs lasers can drive the same process. However, the non-linear absorption of fs pulses means that the same laser can cut disparate transparent materials, all with high edge quality. So laminates (e.g. glass coated with polymide) that are increasingly used in microelectronics and medical devices can be cut in a single pass. The example here shows an edge view of 20 μm of polyimide on 0.5 mm glass, cut with a femtosecond laser with 40 watts of average power and a pulse width ~350 fs. The surface roughness was < 350 nm, as measured with an AFM.

Miniature Metal Gears: USP lasers are ideal for cutting small shapes from thin metal substrates. A standout example involves the small gears used in wristwatches and other precision mechanical systems. The ExactCut is ideal for these tasks with near infrared ps lasers such as the HyperRapid NX being the preferred choice. This combination delivers the requisite edge quality without any post processing requirement, and with no risk of any thermal distortion or discoloration of the gears. A similar setup with an ultraviolet version of the same laser is used to cut the tiny electrodes used in certain neurosurgical implantables.

Surface Texturing of Metals: Lasers have long been used to texture metal surfaces for a variety of reasons. This includes texturing (titanium) dental and other implant surfaces to match the dimensions of osteocyte cells and thereby support optimum bone fusion. It has also included the use of carbon dioxide and excimer lasers to texture the cylinder liners of diesel engines to lower friction and thus extend life and increase fuel economy.

Most early applications used the laser to produce a random pattern of surface features appropriate to the application. But the high peak power and high repetition rates of the new ps and fs lasers enables these to be used to deterministically produce surface features of specific dimensions and in a controlled pattern. A major area of interest for this type of texturing is to manipulate the tribological properties of moving parts in diesel and gasoline engines where a dimpled pattern (like a golf ball) retains lubrication, minimizes friction and wear, and helps manufacturers in their relentless quest for increased fuel efficiency.

Summary

To summarize, USP laser materials processing is a rapidly growing area that is extremely dynamic in terms of the core laser technology. In addition, ongoing advances in laser packaging and integrated tools make these cutting edge products cost effective and practical for the many applications that can benefit from their unique capabilities.

This article was written by Thomas Schreiner, Ernst Treffers, and Michael LaHa, Coherent, (Santa Clara, CA). For more information, contact Mr. Schreiner at This email address is being protected from spambots. You need JavaScript enabled to view it. or visit here .