Re: Specific light wavelengths amplification and visualization

Hmmmm. I can think of a very easy way, a not-so-easy way, and a nearly impossible way to see only light of some specific wavelength; it all depends on what you mean by "intensify" in your question. Let's go in order of simplicity.

If you just want to REMOVE light of all other wavelengths, so that you see only the natural light within a certain narrow passband coming from your surroundings, all you need to do is look through a filter. You can find plenty of cheap narrowband filters, if you don't care which wavelength in particular you will see.

For example, many companies make filters which allow you to look safely at the Sun. Some of these filters allow only a very narrow range of wavelengths to pass through, rejecting over 99.99% of the incoming light. The most common choice for the permitted wavelength is about 656.3 nm, called "Hydrogen alpha" or "Balmer alpha". Light of this wavelength is emitted and absorbed by hydrogen atoms in an excited state, and there's a lot of excited hydrogen in the Sun's photosphere. Looking at the Sun through these filters reveals details that are overwhelmed when all wavelengths are mixed together. Compare this image taken through an H-alpha filter to this image in ordinary white light (a mix of all wavelengths).

How much do these special filters cost? Small filters -- about the size of ordinary eyeglasses -- can be purchased for about $50 and up, while large examples -- a foot or more in diameter -- can cost over one thousand dollars.

Okay, that was the "easy" solution. Let's move on to "not-so-easy."

If you want some particular wavelength that isn't one of the commonly available choices, or if you want to change the wavelength while you watch, then it gets more expensive. There are devices called "tunable filters" which can do what you want. Some of them work by breaking the light into different colors with a diffraction grating. Diffraction gratings, which are simply flat surfaces with many very closely spaced parallel grooves, act much like prisms: bounce light off them, or through them, and you get a rainbow. You can read a bit more about them in this lecture describing diffraction. Light of each wavelength bounces off the grating at a different angle; by changing the tilt of the grating, you can make light of any desired wavelength bounce into a camera or into your eyes.

Another type of "tunable filter" works on a different principle. It uses liquid crystal materials, like the ones in wristwatch or some laptop displays. LCDs induce a "twist", called polarization, into the light rays which interact with them. By combining several layers of polarizing material, one can cause more or less light of all wavelengths to pass through some material -- creating a display with different shades of grey, from dark black to bright white. It might help to look at a very simple description of this procedure at this lecture about polarization and LCDs. Now, with additional layers of material and some ingenuity, one can arrange it so that only certain wavelengths of light will interfere constructively with internal reflections as they pass through a special type of LCD; and by changing the voltage applied to some layers, one can choose exactly which wavelengths will appear bright. So one could build a "tunable filter" this way, too.

You can expect to pay many thousands of dollars for tunable filters, which will also require control electronics, power supplies, and maybe a computer.

You wrote that you wanted to "intensify" light of a specific wavelength. One way to do that is to start by looking through a filter which passes only a small range of wavelengths. The view will be dim, of course, because most of the light is being blocked. You can boost the light level to some degree by sending the filtered light into an image intensifier, or intensified camera. These devices convert a single photon of light into tens or hundreds of photons, making a scene appear brighter. You can read a bit about how they work, or look in the references in that page for more details. You may have seen image intensifiers in action if you watch TV shows or movies about soldiers using night-vision goggles. You can purchase image intensifiers for as little as $1000 or so, though the really good ones cost much more. These devices aren't perfect: they add some noise, like the "snow" you see on old TV sets, to their views.

Okay, let's move on to the "nearly-impossible" answer to your question. In theory, if you want to make a very cleanly intensified version of the light in a very, very small range of wavelengths, you can use a laser. The acronym "L-A-S-E-R" stands for "Light Amplification by Stimulated Emission of Radiation," after all. The basic idea of a laser -- and I'm simplifying a LOT -- is to set up a situation in which a bunch of atoms are all in some particular excited state. They sit there, waiting, waiting, waiting .... When light of the right wavelength passes through this material, it causes one of these excited atoms to emit a perfect copy of the photon: same wavelength, same direction, same phase. The two photons continue on their way, and each can cause another excited atom to emit another copy; that makes 4 photons. Each of THESE continues, and may cause another copy to be emitted; that makes 8. And so on, and so on, and so on. The original beam of light, which might have been very weak, turns into a stronger copy of itself. You can read more about lasers in all sorts of books and web sites; one place to start is the How Stuff Works entry for "laser".

This would be the "best" way to make an intensified version of a scene in some particular wavelength -- the most faithful copy -- but it would be expensive and very difficult to arrange in a practical way.