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The Photonics Spotlight

Beams of Laser Pointers: Visible in Air?

Posted on 2010-01-11 as a part of the Photonics Spotlight (available as e-mail newsletter!)

Permanent link: https://www.rp-photonics.com/spotlight_2010_01_11.html

Author: Dr. Rüdiger Paschotta, RP Photonics Consulting GmbH

Abstract: It is explained why the beam from a green laser pointer is much better visible in air than for a red laser, even though the difference in output power is not that large. The main reason turns out to be the wavelength-dependent sensitivity of the human eye.

Dr. Rüdiger Paschotta

Ref.: encyclopedia articles on laser pointers, laser beams; Wikipedia article on Luminosity function

I have two laser pointers: a small red one, and a larger green one (see the figure).

laser pointer
Figure 1: A green-emitting laser pointer, containing a tiny diode-pumped frequency-doubled solid-state laser.

When I take the green laser and shoot into the night sky, I very clearly see the beam in the air over a large distance. When I do that with the red laser, however, hardly anything is seen.

There are three reasons for that remarkable difference:

In combination, one should expect that the visible brightness of the scattered light from the green laser is much larger than for red light. And this perfectly fits to the experimental experience!

This article is a posting of the Photonics Spotlight, authored by Dr. Rüdiger Paschotta. You may link to this page and cite it, because its location is permanent. See also the Encyclopedia of Laser Physics and Technology.

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