News Details
DPSS Lasers Overcome Glass Process Challenges
2012/9/20 13:52:56
Higher-power and higher-beam-quality lasers continue to emerge on the marketplace, and industry continues to find new uses for them. In particular, glass processing has garnered much attention in recent years. Common tasks such as cutting, grooving, milling and drilling are routinely performed in various types of glass and with various types of lasers. More advanced processes such as annealing, welding and refractive index modification �C for waveguide and diffractive optical element fabrication, for example �C are also being explored. Markets and applications using such processes are quite varied, ranging from the routine to the exotic; and they will undoubtedly grow and diversify as industries discover more about what lasers can do in terms of noncontact structuring of glass. Processing glass with lasers is not without challenge. The fact that glass is transparent to the most commonly available laser wavelengths requires that high peak intensities are generated to trigger a nonlinear absorption effect. With good beam quality, high pulse energies and short pulse durations, such high intensities can be generated in the glass with relatively long-focal-length lenses. This, combined with high pulse repetition frequencies of hundreds of kilohertz for high throughput, is helping to make laser glass processing a feasible solution for a growing number of industrial applications. Laser technologies for glass Various types of lasers are used for different types of glass machining tasks. For full-cutting long straight lines in thicker glasses, carbon dioxide (CO2) lasers are commonly used. In one approach, the focused laser beam heats the glass and is followed by a cooling gas or liquid, resulting in a straight-line fracture of the glass achieved at relatively high speeds �C meter lengths can be cut in a matter of seconds. This approach, however, is not generally successful for thinner glasses much below about half a millimeter in thickness. In addition, any desire to cut curved contours cannot be addressed. Compared with CO2 lasers, ultrashort-pulse (USP) lasers with picosecond and femtosecond pulse widths are at opposite ends of the spectrum in terms of cost per watt and technological complexity. But these lasers also are used for glass processing because they can machine various intricate shapes in glass with very high quality. The quality is excellent because nonlinear absorption phenomena allow small irradiation depths, resulting in controlled material removal and corresponding edge chipping dimensions down to 10 µm or less. However, for the same reason that good quality is achieved, the processing also is relatively slow, with centimeter-diameter holes in 1-mm-thick glass requiring minutes of drilling time. This technology is appropriate for value-added applications, in which the high cost and low throughput of the laser are acceptable because of the uniqueness of the result.