Process for Structural Alteration of Selected Material ("Micro-Engraving")
Summary This invention is comprised of methods and apparatus required to record and read-out a two- or three- dimensional, information-bearing image (pattern) inside a transparent material, with sub-micron features. The technique involves using an ultra-fast (100 femtosecond) laser to induce localized, high-contrast changes in the material's refractive index, without causing damage to the surrounding material. The method has been demonstrated using various glasses, fused silica, sapphire, ionic crystals, and plastics.
Applications Traditional laser machining technologies use nanosecond pulses of light to ablate material away at its surface. These pulses cannot be used to create high-resolution features inside transparent materials, since they produce cracks in the material surrounding the features. The present invention describes a method for creating crack-free, regularly shaped structures in the bulk of a material. Any wavelength (IR through UV) of light can be used, and information can be written in two- or three-dimensions inside the material. Depending on the method used to write the image, it can be visible by eye under normal lighting, or viewing can require a microscope with proper illumination and focusing. Since the surface of the material is completely unaffected by the writing process, the technology is ideal for creating decorative images in glass or for writing covert markings in fine crystal to prevent counterfeiting.
The technology can also be used for permanent storage of digital information. Up to 100 Terabits of information can be stored on a CD-ROM sized disk, and can later be read out with a variety of (potentially inexpensive) microscopes. As the technology can be applied to virtually any micromachining task performed inside the bulk of a material, it can also be used to create optical elements such as diffraction gratings and waveguides.
Glezer, Eli N.
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