Okay, I'm going to give an answer before I read everyone else's, so if I repeat something forgive me, please.
What you see is what is entering your eye. When the laser light re-enters the atmosphere, the wavelength goes back to whatever it was in the air, then upon entering your eye, whatever the wavelength is in the vitreous humor. "But", you say, "shouldn't that be a shorter wavelength and therefore 'green-shifted?'" "Yes, but the cones in your eye don't care about wavelength. They respond to energy deposition which if frequency dependent. It's the energy of a photon which determines the interaction with a cone (3-different types of cones have been identified on the retina).
All in all, color detection by the eye seems to be frequency dependent, not wavelength. We've just assigned color names to wavelength ranges. I don't know how CCD's work (I guess I could look it up but I'm at home listening to the rain), but I would guess they are photon dependent which means frequency, not wavelength.
Bill Nettles
________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Anthony Lapinski [Anthony_Lapinski@pds.org]
Sent: Friday, April 23, 2010 6:49 AM
To: phys-l@carnot.physics.buffalo.edu
Subject: [Phys-l] refraction question
When sound waves refract, the frequency always remains constant. Thus, if
the velocity decreases, the wavelength also decreases. This same idea
holds for light. When light refracts, the frequency remains constant. But
how does this relate to the COLOR of the light? Does the color depend on
frequency or wavelength?
The reason I ask is that suppose you shine red light (say, 680 nm) from
air into water. Since n = 1.33, both the velocity and wavelength will
decrease by this factor. Thus, (680 nm)/1.33 = 511 nm. This is the
wavelength of green light! We've probably all done this demo with a red
laser, and the beam remains red. So color depends on frequency. In class I
usually say that color depends on wavelength. Lasers are rated by their
wavelength. Instead, should lasers -- like tuning forks -- be rated by
their frequency since this quantity never changes?