High Energy Laser Myths

This will take several postings.

Opponents of the High Energy Laser (HEL) development community have a list of reasons that HEL will never work. It is a list of the reasons given by critics who question spending defense funds in an area they consider futile. A reason that almost always appears is that defense against HEL weapons is as easy as painting weapons to reflect the laser energy.

That seems intuitively obvious. We all see our reflection in mirrors and we understand that the reflection is merely light returned to our eyes because the mirror is coated with something that does not let the light pass through. This is a case where intuition turns out to be wrong. Theoretically, you could coat and polish a warhead or weapons platform to reflect the laser energy and in fact, that is exactly what is done on the optics that collect, shape and direct the laser beam in an HEL system. Until the mid-1990s, those optics were cooled using high flow-rate liquid coolant systems. Think of those cooling systems as really big automobile radiators. Hundreds of gallons of coolant were required to keep the optics system from burning up when the HEL hit it. Even then a small flaw in the optic could result in a hot spot and blowout of the optic. A cooled optic could cost millions of dollars to produce and polishing and recoating ran hundreds of thousands. In the mid-1990s, uncooled optics became available. These cost an order of magnitude less than similar sized cooled optics, but still cost tens of thousands for even the smallest. The coating and polishing of the optic is a costly, high-precision job.

Another aspect of HEL optics is that the reflective coating is designed for a particular wavelength. The optic that works well for a deuterium-fluorine HEL works less well for a hydrogen-fluorine HEL. More energy is absorbed by the optic and less reflected when the coating is not optimized for the wavelength. In fact, a coating may enhance the energy adsorption of an HEL beam rather than reflecting it.

So theoretically, weapons platforms and projectiles could be coated and polished to reflect laser beams, but it would be very expensive to do so and it would only be effective if you know the exact characteristics of the laser you are defending against.