Can a laser beam be seen from the side?

Under most conditions, a laser beam cannot be seen traveling through the air. Since our eyes are essentially light collectors, we can only see light that enters the eye and is imaged onto our retina. When a laser beam encounters dust, mist, or smoke, some fraction of the light is scattered in the direction of the viewer's eyes and therefore becomes visible. Since these particles are rather small and will not stop the entire beam, all the tiny reflections make the beam look solid or continuous. This is why the beam appears to slowly fade as the dust (or scattering medium) dissipates. In the absence of any type of scattering medium, the beam will only be visible as a spot when it reaches its target and energy reflects back to the viewer. This principle can easily be demonstrated by using a flashlight on a dark night: if it is foggy, you can see the cone of light coming from the flashlight; if it is not foggy, you can only see the light as a spot at its target. If you see something that appears to contradict this concept, it is usually just 'movie magic'.