We've had a quiet day up at SALT with all the locals off enjoying Hertiage Day & the longish weekend. David continued his relentless onslaught on the HRS documentation.
& we got going on the throughput tests in the blue, using bright LEDs with peak wavelengths of 460 nm & 505 nm.
The test setup actually works really well & we were heartened to get the same results at 460 nm using two different calibrated diodes. The second diode runs out at 500 nm so we could only repeat the bluest measurement, but this was enough to give us confidence that our numbers are sensible.
Along the way we found that one of the High Stability (HS) mode fibres was substantially down in throughput. We went in to take a look at the scrambler ends & soon found the problem...
Fibre HSN was broken just inside the silica ferrule, where it goes into the stage on the input side of the scrambler. One can clearly see the light bleeding from the wounded fibre on the right - compared it to the non-glowing ferrule plugged into the stage on the left.
By projecting the light emerging from the fibres onto a screen we could see that the spot on the right's fainter & bears an ugly scar.
Fortunately, this is about the best possible place to suffer a break as the fibre can be repaired fairly easily, & of course we have two spare fibres in position as well. We can't find the spare glass ferrules & suspect that they may still be in Durham, so instead we'll just swap in one of the spare fibres.
To do this, we first had to break the glue that attaches the fibre to the lens.
& then remove the glass ferrule that's bonded into the stage. This was trickier & required the whole piece to be soaked in acetone in order to dissolve the glue. Hence the rest of the repair became "a job for tomorrow".
Besides - being Heritage Day meant that we're culturally obligated to have a braai. Pierre managed to lend additional ceremony to the occasion by bringing Luke a wicked slice of birthday cake from Cape Town, & then setting fire to it with an impressive number of candles!
The weather was Perfect & the evening seamlessly morphed into a spectacularly clear Karoo night with the Milky Way blazing overhead. This kept Jürgen & his beloved Astrotrac extremely busy :) Some pics to follow once he's done all the processing!
Supreme Braai Masters Garith & Deon (from the unlikely quarters of IT & Software, respectively) did the honours, cooking us up a storm! Thank you guys - the HRS team needed to see how this is done :)
Now for the shot of the night: our awesome IT duo, in uniform & sporting their special-issue Sutherland antennae... For the record - this perfect chance-alignment was captured completely unintentionally, no Photoshop required!