dr-ebert
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3 weeks ago I bought a couple of [URL="http://laserpointerforums.com/f39/fs-cheap-diffraction-grating-glasses-3-a-41855.html"]these diffraction glasses[/URL] from Alexzupinhea. After they arrived, I played around with them a bit and came up with two simple-to-do experiments which may have some practical merit for one or the other. The first one is on how to check your lasers wavelength. This one, the second one, has a more qualitative nature: to check the fluorescence spectrum of substances under the influence of a BR laser.
There are two ways you can use your diffraction glasses:
1. Shine your laser through them and watch the beam being split into a multitude of dots.
2. Wear the glasses while shining your laser at a target and also watch a multitude of dots.
In the first case, the laser beam is actually split into multiple beams, each creating their own spot. In the second case, the light reflected from the spots can take multiple paths into your eyes and so you seem to see several spots.
Because the angle of diffraction is wavelength-dependent, generally objects will seem to have a rainbow-colored halo or fuzziness when wearing these glasses. Since lasers have only a single wavelength (actually a very small spread of wavelengths), this does not play a role in case #1 above.
However, if the beam causes fluorescence, the dot will emit other wavelengths as well. The different colors will then be spread into a spectrum in case #2.
And this is how a white piece of cloth looks under a BR beam:
You've probably already noticed that white clothing lights up brightly bluish-white under a BR beam. That's because washing machine detergents contain brighteners that make white look extra-white if there's some UV around.
Here's the spectrum from some Playmobil toy (a torch from the various castles they have), which shines bright pinkish-red under the BR beam:
One of the most famous fluorescents is fluoresceine, which has a yellow-greenish light that is very visible. It is in many of those yellow-greenish transparent plastics you encounter, for example, in some Lego blocks. Here's the spectrum.
I have as yet not found a substance that does not have some fluorescence. The least amount I've encountered (and thus the one that shows the BR color most naturally) is the enamel in bathtubs and white bathroom tiles. Here is the spectrum, you can see that now the fluorescence is much weaker than in the previous cases - it's only barely visible in the first-order diffraction.
And that's it folks.
EXERCISE FOR THE INTERESTED STUDENT:
devise a method to prove that the spectrum in the last picture is really due to fluorescence of the target and not already contained in the laser light (e.g. due to contaminations in the beam path).
There are two ways you can use your diffraction glasses:
1. Shine your laser through them and watch the beam being split into a multitude of dots.
2. Wear the glasses while shining your laser at a target and also watch a multitude of dots.
In the first case, the laser beam is actually split into multiple beams, each creating their own spot. In the second case, the light reflected from the spots can take multiple paths into your eyes and so you seem to see several spots.
Because the angle of diffraction is wavelength-dependent, generally objects will seem to have a rainbow-colored halo or fuzziness when wearing these glasses. Since lasers have only a single wavelength (actually a very small spread of wavelengths), this does not play a role in case #1 above.
However, if the beam causes fluorescence, the dot will emit other wavelengths as well. The different colors will then be spread into a spectrum in case #2.
And this is how a white piece of cloth looks under a BR beam:
You've probably already noticed that white clothing lights up brightly bluish-white under a BR beam. That's because washing machine detergents contain brighteners that make white look extra-white if there's some UV around.
Here's the spectrum from some Playmobil toy (a torch from the various castles they have), which shines bright pinkish-red under the BR beam:
One of the most famous fluorescents is fluoresceine, which has a yellow-greenish light that is very visible. It is in many of those yellow-greenish transparent plastics you encounter, for example, in some Lego blocks. Here's the spectrum.
I have as yet not found a substance that does not have some fluorescence. The least amount I've encountered (and thus the one that shows the BR color most naturally) is the enamel in bathtubs and white bathroom tiles. Here is the spectrum, you can see that now the fluorescence is much weaker than in the previous cases - it's only barely visible in the first-order diffraction.
And that's it folks.
EXERCISE FOR THE INTERESTED STUDENT:
devise a method to prove that the spectrum in the last picture is really due to fluorescence of the target and not already contained in the laser light (e.g. due to contaminations in the beam path).
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