Formation of Hollow Beams Through Coherent
Dhruv Bansal, The Wheatley School,
Harold Metcalf and John Noé,
Laser Teaching Center, University at Stony Brook 11794-3800.
Fiberoptical cables are microscopically thin flexible glass rods which
transmit light through total internal reflection. When a group of these
microscopic cables are fastened together, the result is a fiberoptic
bundle. This bundle passes light unchanged through its length.
Most lasers produce a small highly focused dot of light. It is possible,
through the use of a special Axicon lens, to refocus this light into a
ring without losing too much intensity. The new beam will be a hollow
cylinder. Hollow beams are used to trap atoms when one does not want the
light interactions that might result using a conventional beam.
In the Laser Teaching Center, it was recently discovered that a diode
laser, shined parallel to the axis of the fiberoptical bundle, will
produce a wide dot, just as expected. If the laser is tilted off axis,
however, the dot becomes a ring. This ring has much the same intensity as
the original dot. As a result of this phenomenon, it may be possible to
use simple fiberoptic cables as a means of producing hollow beams as
opposed to using a more expensive and less versatile Axicon lens.
My project involved determining the optics of a fiberoptical bundle. By
varying entrance angles and the aperture of the bundle, I was able to
determine what optical devices were at work inside the cable.
Through the use of a simple photodetector, I will soon be able to measure
the Gaussian profile of the ring.
Hopefully, this new phenomenon will be an alternative to more expensive Axicon lenses in producing hollow beams.