How to test LGSW entrance window transmissivity

Measure LGSW entrance window in transmission

1. Setup the LGSW for daytime activity: deploy calibration source and align the hexapod to feed the LGSW
2. Adjust the current value of the calibration source to get a ~10000 counts/subap on the blue pupil looking at the PnCCD viewer
3. Note the calibration diode number corresponding to blue pupil and its current value
4. Switch off the other 2 diode sources
5. Go up on the telescope, mark the fibers coupling to the diode module in the CalSource rack and then unplug all fibers
6. Plug, once at the time, all the 3 fibers on the active diode source
7. Take a snapshot and write down the flux value on the illuminated pupil

Measure LGSW entrance window in reflection

1. Switch on the LGSW internal source diodes
2. Adjust the current value of the calibration source to get a ~10000 counts/subap on the blue pupil looking at the PnCCD viewer
3. Write down the diode number and current value
4. Switch off the other 2 diode sources
5. Go up on the telescope, mark the fibers coupling to the diode module in the LGSW rack and then unplug all fibers
6. Plug, once at the time, all the 3 fibers on the active diode source
7. Take a snapshot and write down the flux value on the illuminated pupil

Evaluation of the differential LGSW EW transmissivity

The ratio between the pupil flux recorded in transmission and reflection should give a hint of the EW transmissivity. Obviously this is not an absolute transmissivity measurement, but only a differential one with respect to the blue EW value that has been taken as a reference.