Abstract:
In recent years, femtosecond lasers have been used for a multitude of micromachining tasks. Several groups have shown that femtosecond laser pulses cleanly ablate virtually any material with a precision that consistently meets or exceeds that of other laser-based techniques, making the femtosecond laser an extremely versatile surface micromachining tool. For large bandgap materials, where laser machining relies on nonlinear absorption of high intensity pulses for energy deposition, femtosecond lasers offer even greater benefit. Because the absorption in a transparent material is nonlinear, it can be confined to a very small volume by tight focusing, and the absorbing volume can be located in the bulk of the material, allowing three-dimensional micromachining. The extent of the structural change produced by femtosecond laser pulses can be as small as or even smaller than the focal volume. Recent demonstrations of three-dimensional micromaching of glass using femtosecond lasers include three-dimensional binary data storage, and the direct writing of optical waveguides and waveguide splitters. The growing interest in femtosecond laser micromachining of bulk transparent materials makes it more important than ever to uncover the mechanisms responsible for producing permanent structural changes.