Yoel Fink perfect mirror / Bragg fiber development

MIT doctoral thesis ~1998 developing dielectric mirror via index-of-refraction layering, with quantum-confined reflection. First application: laser surgery fiber optics. Now used for higher-power laser welding.

The electron beam is affected by magnetic fields, and you can manipulate it with magnetic fields; with lasers you use mirrors or fiber optics. One of the advantages in recent years for laser heat sources is the fiber optics have gotten better and better. Professor Yoel Fink of this department did his doctoral thesis developing basically a perfect mirror. You put different layers of different index-of-refraction materials and you can get a quantum effect such that the light cannot go through, so it has to reflect back. The first big application of this, when he was a young professor about 15 years ago, was to make fiber optics for laser surgery — high-value-added medical business. But now people are using some of these things for higher-power lasers such as laser welding. So you can use fiber optics to get the beam there. In the old days you had to use mirrors. And I already told you the problem with mirrors — you get any dust on the mirror, when the laser beam hits it, it couples very well to the dust because the dust is an insulator, not reflective, and you burn a pit right in the surface of your mirror. You can destroy some very expensive optics very quickly.