Laser-Solid Interactions for Materials Processing

By focusing femtosecond laser pulses with high numerical-aperture microscope objectives, we micromachine optical glass using energies that are in the range of modern laser oscillators. When a femtosecond laser pulse is tightly focused inside a transparent material, energy deposition occurs only at the focus, where the laser intensity is high enough to cause absorption through nonlinear processes. When enough energy is deposited, a localized change in the index of refraction is produced, i.e. the material is damaged. By scanning the focus through the sample, very precise, three-dimensional microstructuring can be achieved. The diameter of the single-shot damage spots is less than 0.5 mm. We have investigated the dependence of the damage threshold and morphology on the numerical aperture of the microscope objective, the wavelength of the laser, the bandgap of the material, and the energy of the laser pulse. The potential of our technique for producing industrially-relevant structures such as waveguides and Bragg gratings, as well as the advantages of micromachining with only an oscillator instead of a complicated, expensive amplifier chain will be discussed.