Beam Laser Pointer

Beam Laser Pointer

Why we cant see red laser pointer beam (we have to use smoke to reflect the beam)?

but we can see green laser beam without smoke. Is that because of power , if so could someone explain in details it.

Actually, you can only *see* the laser beam when the laser light scatters off air molecules or air particles and the scattered light goes towards your eye. So, when you add more particles, like smoke, there are more chances for the light to scatter toward your eye.

Now that we we've discussed how you *see* a laser beam, I can answer your question about red versus green light. Laser light comes in different wavelengths, the shorter the wavelength the more blue the light looks, and the longer the wavelength, the more red the laser light looks to us. How well laser light scatters off air molecules depends on it's wavelength. The shorter the wavelength, the better it scatters light. This is called Rayleigh scattering, and it is proportional to 1/(wavelength)^4. So where is this all going? The green laser beam emits light of a shorter wavelength than the red laser does, so it scatters off just the air well enough for you to *see* the beam.

Your question about power also is relevant. If the power emitted by the red and green lasers was the same, then what we discussed about Rayleigh scattering would apply. If you increase the power of the laser, you increase the number of photons of emitted (the quantitized packets of light, if you haven't heard of these before, don't worry about it, but you can think of them as tiny particles of light). When you increase the number of photons, you increase the chance that enough photons will scatter off the air molecules so that you can *see* the laser beam.

Hope this helps! Let me know if you want to know more!

Beam Laser Pointer

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