Alia Sabur, Harold Metcalf and John Noé, Laser Teaching Center, Department of Physics and Astronomy, University at Stony Brook.

When a laser beam is passed through a coherent fiber optic cable at an angle to the axis of the cable, a hollow beam (or ring) is formed. The diameter of this beam is proportional to the angle that the laser makes with the cable. Hollow beams are used in atom trapping instead of a traditional laser beam, so the atoms are in a dark spot and will not interact with the photons. Hollow beams are typically produced by using Axicon lenses, but Axicon lenses are expensive and fragile to use. I am trying to see if fiber-optic cables can replace Axicons in producing hollow beams. I have been using a photo detector to measure the light intensity profile using a 632.8 He-Ne laser, which I have found to be Lorentzian, not Gaussian (as I expected), like the original laser beam. Also, the ring is not polarized, unlike the original laser beam. The procedure I used was to first pass the laser light through a 3mm hole (not pinhole or there would be diffraction), then into the center of the fiber optic cable and then onto a screen. Because of the way the laser box is built, it was not possible to accurately determine the angle from where the laser starts, because I do not accurately know where the tip of the laser is. My procedure allowed me to measure the angle from the hole to the cable accurately. My results appear to show that fiber optic cables can be used to produce hollow beams in place of Axicon lenses. I would like to do further research with various fiber optic cables and different lasers to confirm this.

Celebration of Undergraduate Achievements 2 May 2001