confusing units discussion in the manual

[stevengj]

The manual says:

• When the lattice vectors are set, this determines a length scale. Suppose we have a square lattice with a periodicity of 680nm. It might be logical then to choose 1 micron as the base length unit, and to specify all lengths in microns. The lattice would then be set to the vectors (0.68, 0) and (0, 0.68). Since frequency is in units of inverse length, then SetFrequency(1) corresponds to a wavelength of 680nm or a physical frequency of (c/680nm) = 441 THz, and SetFrequency(1.1) corresponds to a wavelength of (680/1.1) = 618nm, etc.

However, if you choose units as µm and set the lattice period to 0.68 (that is, 0.68µm), then doesn't SetFrequency(1) set the wavelength to 1µm/1 = 1000nm, not 680nm?

That is, isn't the frequency set relative to the choice of distance units, not relative to the period per se? We have checked S4's behavior against analytical calculations and it seems to match our understanding.

[victorliu]

Ah yes, you are correct. I will fix this when I get home tonight.

On Mar 13, 2014, at 2:11 PM, Steven G. Johnson [email protected] wrote:

The manual says:

When the lattice vectors are set, this determines a length scale. Suppose we have a square lattice with a periodicity of 680nm. It might be logical then to choose 1 micron as the base length unit, and to specify all lengths in microns. The lattice would then be set to the vectors (0.68, 0) and (0, 0.68). Since frequency is in units of inverse length, then SetFrequency(1) corresponds to a wavelength of 680nm or a physical frequency of (c/680nm) = 441 THz, and SetFrequency(1.1) corresponds to a wavelength of (680/1.1) = 618nm, etc. However, if you choose units as µm and set the lattice period to 0.68 (that is, 0.68µm), then doesn't SetFrequency(1) set the wavelength to 1µm/1 = 1000nm, not 680nm?

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