How to Build a Laser Death Ray

Reflective Resonant Cavities

To get around the limitations of self amplified spontaneous emission, you can stabilize the beam using a resonant optical cavity. The simplest form is to use two mirrors that reflect the light back and forth between each other. These mirrors are typically slightly curved, to focus the beam slightly inward (as you can imagine, if the mirrors were flat, even a miniscule mis-alignment would let the beam leave the mirrors eventually. The slight focusing prevents this).

If a rod of gain material is placed in this cavity, with the rod pointing at each of the mirrors, any light which is emitted by the rod toward one of the mirrors will be reflected back and forth indefinitely, passing through the rod and being amplified many times. This serves to average out fluctuations in the beam, giving more predictable and stable output. A well machined set of mirrors will also give a high quality, coherant beam. Although the resulting beam may have a moderately large divergence, it can be focused using mirrors or lenses into a diffraction limited spot because it is coherant.

To extract the beam from the optical cavity, one of the mirrors is typically made slightly transparent. Then, while much of the beam is being reflected back into the cavity, some will escape in the form of a the light beam you will use for your death ray.

Back to main death ray page