Rationale

In each WFS the 3 laser beams follow indipendent path (or "channels") up to the detector. This means that several devices inside the LgswUnit are installed in triplicate, with one device for each channel. It is the case of pupil motors, piezo mirrors, Pockels cells, patrol cameras.

It was decided to follow a naming convention based on colors rather then on numbers: so instead of having channels 1, 2 and 3 (or even worse 0,1 and 2) we have channels Blue, Yellow and Red. This is just a naming convention, it means nothing in terms of spectral properties (every piece of optics is narrow-bandwidth around 532nm!. The 3 channels are identical in terms of optical properties)

We tried to stick to this convention as much as possible. For instance, in the software there is a PupilMotorBlue, PupilMotorYellow and so on. The cables and the connectors of a device sitting in the BlueChannel have (whenever possible) something blue (a ring of blue tape, a blue-plastic shell, ...)

Definition

The 3 beams reflected by the LgswDichroic focus on the entrance flange of the LgswUnit, at the vertexes of an equilater triangle. Suppose the telescope is pointing at zenith, so that the LgswTable is horizontal. The beam on top (the one more distant from the LgswTable) is the Blue one. The one on bottom-left (on the ConnectorPanel side in the DX unit) is the Yellow one. The one on bottom-right (on the ConnectorPanel side in the SX unit) is the Red one.

This geometry is preserved inside the LgswUnit: the beam passing high over the board, close to the cable duct is the Blue one. The beam on bottom-left (with respect to propagation direction) is the Yellow one. The beam on bottom-right is the Red one.

The same applies to the stored frames and to the CCD viewer: the pupil on top is the Blue one, the pupil on bottom-left is the Yellow one, the pupil on bottom-right is the Red one.

Relation with upward beacons

The relation with upward beacons is shown in the picture (the green beam was then renamed "yellow" to avoid possible misunderstanding with the real light color).

-- LorenzoBusoni - 28 Apr 2013