Wednesday, August 17, 2016

Cleaning the collimator main group

The next bunch of RSS lenses to be attended to was the collimator main group - the most complicated of the lens groups.  This unit contains 2 singlets + a triplet consisting of a sodium chloride lens (yes: SALT!), sandwiched between 2 spectacular chunks of calcium fluoride, with coupling fluid filling both the gaps (the butter in the sandwich, if we're inclined to overdo the analogy).

A dusty eyeball
The collimator doublet leaked some of its lens fluid at some point & this oily liquid had found its way down onto the top of the triplet - seen here as the messy streak at 6 o'clock.  Ugh :{

We've found the mystery smudge!
A set of "before" throughput measurements was made on the dirty main group, then Ockert could dive in & do his cleaning magic.

Okkie super-focused on the task!
The powerful combination of sodium lauryl sulphate, de-ionised water & alcohol once again did the trick, even removing the nasty streak of dry lens fluid.

Washing windows
The curvature on the top CaF2 lens in the triplet is really extreme!

Going after those hard-to-reach places
With the outer surface clean, one can more easily see the small droplets of the original lens fluid that still stubbornly refuse to mix with the new coupling fluid.  Fortunately these don't seem to have a huge effect on the optical performance.

Streaks & droplets of the original lens fluid are impossible to remove
The throughput tests were repeated after the cleaning & showed a huge improvement across the entire wavelength range - a gain of approximately 8%!  Awesome :)

Throughput measurements before (red) & after (blue) the cleaning of the main group
An already brilliant day that'd included thunder, lightning & loads of rain (technically impossible in the middle of winter!) + excellent throughput gains got even better when Ockert spotted a meerkat through the north window of the control room!  The more we looked, the more of them we saw & pretty soon a bunch of us were staring at a bunch of them.  From the pic below, one might argue that they were staring at us!  Absolutely delightful creatures :D

Who's watching who?!
So there you have it - we're finally starting to develop SALT/MeerKAT synergies!  We haven't seen these little guys out here before, but presumably they're heading north towards Carnarvon to go run their telescopes?

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