The Physics of Light Propulsion

The Physics of Light Propulsion

Imagine a mode of transportation which allows a craft to ride upon a beam of light. This craft uses virtually no fuel, simply the air around us. The uses for such a craft would be endless, launching small satellites into orbit and in the future launching vessels much like today’s shuttles. This idea is no longer a product of science fiction but rather a reality. It is all made possible by the physics which controls everything in our everyday lives.

There are two main components to this light propelled craft. The light source is a precision high-powered laser beam. The craft is a large, highly polished parabolic mirror that is designed to capture the laser beam. With the laser in a fixed position on the ground the mirror focuses the beam, rapidly heating the air, creating a wave of heated air out the back. This forces the vehicle in the opposite direction. As the beam is rapidly pulsed, the vehicle is continuously propelled forward.

The laser pointer which many people now carry around on key chains was not thought as such a trivial toy or gadget ten years ago. The laser technology itself is a very complicated endeavor. The simple circuitry has evolved from years of work to make the theory behind the amplification of light possible.

Light Amplification by the Stimulated Emission of Radiation or LASER, is best understood by beginning at the atomic level where the basis of an atom and its energy levels can be identified. In even the most basic chemistry class the atomic structure is one of the first lessons which is taught. The circular shells of an atom are placed around the nucleus with the electrons placed on these levels. Two in the first layer, eight in the next continuing on to the appropriate number.

These shells are formed because electrons are limited to a series of fixed values, this is an example of quantization1. The law of conservation of energy is applied in that an electron may fall to a lower shell, but in doing this it must give up an amount of energy equal to the difference between the two levels. This energy is given up as light.

Light is also considered to be quantized. It can be represented as groups of photons. Each photon carries one quantum of light energy. The amount of energy in a quantum depends on the wavelength of the light or the frequency.