| MadSci Network: Physics |
Hi Raja,
Thank you for your question. I've been reading up a bit on white lasers. The only broad-spectrum laser I was familiar with is the Ti:Sapphire laser [1], but that lases in the red part of the spectrum. It also has a very high power density (chiefly because the pulses are so short), making it impracical for the purpose you describe.
I think the laser you are discussing is the one in [2, 3]. Basically, the researchers created "white" light by combining red, green and blue light from a laser. They did this by modifying the lattices in their laser cavities. What is also impressive is that they are quite efficient.
The reason I put "white" light between brackets is because true white light contains "all" wavelengths. I am not sure there is an universally agreed definition of what white light is, but I think sunlight comes quite close (the Sun only looks yellow because the blue light is scattered over the sky; it looks quite white from space. On Earth, the best we could do to approximate this is a black body [4] with a temperature roughly equal to that of the Sun, which is 5800 K or so [4].
Now, with this laser, red, green and blue light are created. When this hits a white objects, say a piece of paper, the light is reflected. To our eyes, this looks like white. However, the light is not really white. This is evident when it hits something that is not white. As an example, if the "white" light hits something orange that reflects a narrow range of colors it will look greyish instead of its true color. In other words, by making the laser emit something closer to real white light, it would need to produce more than three colors - the more the better, provided they are distributed over the spectrum.
This brings me to the question: is it possible to produce more colors? The technique used seems generic enough, although it is technically challenging to add more colors. Furthermore, even though you would have more colors, getting a true continuum might be quite hard, as each laser still requires its own optical cavity.
Have a good day,
Bart
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