Published on: Thu Nov 11 2010
Today I stopped by the LTC and Dr Noe was explaining to me how a laser works by reflecting light back and forth between two mirrors, one which is 1% transparent which is where the visible laser beam emerges from.
This lead to a plot showing the gain vs the frequency, and Dr Noe was talking about the modes of the laser. I had not heard of modes before, and wanted to know more about them. So the length of the gas filled tube between the two mirrors is equal to the number of Nodes times the wavelength divided by two.
Inside the Gain vs Frequency plot, the frequencies are really only amplified at a few specific frequencies (which are somewhat distributed (fuzzy?) because of the Doppler shift). Those amplified frequencies are the modes of the Laser. I think the change in frequency between each mode was this Very Important Formula: Delta f = c/2L
We also looked at an open cavity laser (Neon Hydrogen! it's spectrum was huge), so I could see how the light bounced back and forth from the gas between the two mirrors. We looked at the Temporal (Length / Longitudal) and the Spatial Mode (HG Mode).
Modes are a set of numbered solution functions.