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In addition to the primary laser characteristics, there are several factors to consider for achieving a stable process. Beam quality, in conjunction with lens focal length and input beam diameter, will determine the focal spot size, and the depth of focus, essentially the “drill bit” diameter and length. Assist gases are also used for several reasons. One reason is to protect the lens or cover slide from ejected matter. Gas can also infl uence the drilling rate. Gases can also assist in removal (O2) or help reduce oxides (N). Pressure/fl ow must be balanced to protect the lens without suppressing the expelled material. Gases should be free of moisture. Laser drilling has been demonstrated at aspect ratios (depth/diameter) of greater than 20.


Micromachining with Lasers Laser micromachining involves the machining of small features into various materials using lasers through material removal. By “small,” the feature size is usually less than 1 mm, with a material thickness less than 1 mm, and both are usually a lot less.


Lasers are used for a variety of reasons. First, the noncontact nature minimizes the risk of damage to the material and does not introduce tool wear. The feature resolution when using UV lasers is unmatched by any traditional machining technology, with the smallest attainable features on the order of a few microns, using UV lasers and high-quality optics. By choosing the correct wavelength and energy density on target, selective material removal can even be achieved. Finally, the use of lasers provides great fl exibility espe- cially in the prototyping and R&D stages. For micromachining applications, the key to clean and low taper processing is peak power inten- sity: energy density per unit area. In other words, the best results are obtained using lasers with high-pulse energy and short-pulse length where the laser spot is focused to a small size. This is one reason USPs (ul- trashort pulse, meaning picosecond and femtosecond lasers) are becoming popular: The short-pulse length greatly increases peak power at the target, even with relatively low pulse energy.


The First Step to Reliable Laser Performance


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