|MadSci Network: Physics|
There are two possibilities. Number one is that the laser is not really a single line, but there is a faint orange-yellow line present as well. As the laser light passes through the glass the longer wavelengths are refracted more than the shorter wavelengths and thus become separated from the beam. You can test this by passing the beam through a diffraction grating. The grating will split up the beam into its component parts. You could also try a prism, but the grating will work better. The second, less likely, possibility is that you are seeing fluorescence. The glass atoms are absorbing the laser photons then re-emitting photons at a longer wavelength. Usually this will not occur in optically pure glass, but rather it happens in glass that contains some impurities or dye. My guess is that you are seeing the orange-yellow line that is already present in the beam. Argon lasers emit at least four colors of visible light, but the green-blue color is by far the brightest. With a grating you should be able to see violet, blue, blue-green, and orange-yellow light. Good luck!
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