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We study the interaction of intense, femtosecond laser pulses with bulk transparent materials and use this interaction for material modification. The intensity of a femtosecond laser pulse can be high enough to cause nonlinear interactions between a transparent medium and the laser field. The material can strongly absorb energy from the laser field, producing free electrons in the material. This absorption can lead to damage or refractive index changes in the irradiated sample. The nature of the interaction between the laser pulse and the material depends on how the laser pulse is focused. When a powerful femtosecond laser pulse is tightly focused into a transparent sample, nonlinear absorption occurs only in the very small focal volume. This localization allows us to create patterns in three-dimensions inside transparent samples such as glass. For example, we have observed structures as small as 200-nm in diameter, offering exciting possibilities for high-precision microstructuring of transparent solids and for minimally disruptive laser nanosurgery.
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Optical data storage in glass using femtosecond laser micromachining. |
Three-dimensional polymer structure fabricated on a glass substrate. |
The nonlinear interaction can also be used to grow structures on the surface of a substrate. By coating substrates with carefully prepared transparent chemical mixtures, we fabricate polymer and metal structures on glass substrates. We apply the method to create devices with applications ranging from photonics to biology. We are optimizing the metal patterning technique to fabricate metamaterials in three dimensions. These metamaterials, which are engineered optical materials, could have applications ranging from superlensing to negative refraction.
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| Plainly Speaking | Usually when light goes through a piece of glass, nothing happens to either the light nor the glass, i.e. the glass is transparent. With a powerfull femtosecond laser pulse, both the laser light and the glass can be changed. When we concentrate the laser light using a microscope lens, we produce a microscopic explosion inside the glass, which leaves behind a minuscule ball-shaped hole. We use microexplosions as a miniature "punch" to make patterns inside glass for such applications as high-density data storage. Microexplosions can also be used as a high-precision laser scalpel -- we have been able to eliminate a single cell in a skin sample, without affecting the neighboring cells!
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Array of microscopic holes in glass produced using a femtosecond laser
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In addition to patterning glass and cutting cells, we can also grow structures in three-dimensions. We use femtosecond laser pulses to grow polymers and metals on glass substrates for applications ranging from cell migration studies, to making engineered optical materials.
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