Mounts for toys & physio for a spectrograph

As much as Francois seemed to enjoy crawling around on the floor to play with the interferometer & CGH, the new vertical mount on the optical table lends a considerable level of class to the operation...

& while the bazooka look worked for Darragh, the alignment telescope does better in its mount as well...

Meanwhile, in the spectrometer room, the Robert Stobie Spectrograph (RSS) crowd's been very busy getting the optics back in & aligned, then testing the various mechanisms... Looking good!

Cosmology in the clean room

The SALT Image Quality problem would appear to be a cruel manifestation of Dark Energy! Our recent interrogation of the M4/M5 pair with a wavefront camera has yielded startling results: we are able to trace the history of the Universe (from the initial fireball, through inflation, galaxy formation and finally our accelerated expansion toward oblivion) by simply running the wavefront camera through focus. See it all in our pinhole astrophysics clip below...

Diet Coke + Mentos reaches Sutherland!

We now have the null lens the manufacturers used to test M2 so once the chaps figure out how to mount & align the various components, we'll be able to repeat that test to check the figure of M2.

The alignment telescope will come in useful too so it's time to check out how that works.

Since most people here weren't familiar with the extraordinary Diet Coke & Mentos phenomenon, it was decided that a demonstration was in order. Carl obliged & managed to avoid being showered, but next time we need a deployment mechanism for the Mentos & some sort of nozzle!

Our eagerness to get back to Cape Town was no match for the urge to learn a new Zemax trick from the guru in the driver's seat - not much worse than chatting on a cell phone while driving ;)

Pinhole scans with the wavefront camera

We spent time playing around with the wavefront camera - more fun than it sounds! By moving the pinhole around in X & Y about the position for the best image & following it with the wavefront camera, you clearly see coma - the dominant off-axis aberration in a system. The analysis software also determines the contributions from the other aberrations: astigmatism, spherical, trefoil & more. Images were obtained for a 5x5 grid with 0.5 mm offsets in X & Y - the resulting sets of point spread functions & interferograms are shown below.

Drilling & pinning M4!

M4 looks like an upside-down mushroom. The stalk's bonded into an invar cup, which is bolted into a steel cup that's attached to the 3 vanes that make up the M4 spider. The idea was to insert a pin to thoroughly secure the invar to the steel cup to be sure that M4 can not move around At All.

The man for the nerve-wracking assignment of taking a drill to the SAC was Craig. Part of the extensive preparations included reserving a space for him in an undisclosed Northern Cape branch of the Witness Relocation Programme on the off chance that things might go badly.

With M5's cover in place, an optical diaper on M4 & a lot of plastic in place to catch any swarf the vacuum cleaner might miss, the drilling jig was attached.

We decided to make this seem easy by taking the super-structure off after Craig had psyched himself up for drilling with it in place - much better idea!

James on Swarf-Sucker duty...

It was all done before we knew it & Craig could go off for a hard-earned smoke break - great job!

We're baaaack!

Drove back up yesterday admiring the Hex River valley's autumn colours & first snow of the season...

& a classic Karoo scene: a person idly waving a small red flag at the side of the road for no apparent reason. A bit further on, another one. Then around a sharp corner one promptly discovers the huge flock of sheep they were alluding to - OH, Right!

The mechanical chaps set about trying to stabilize the jittering fringes we were getting with the interferometer. The pneumatic isolators were tuned up & a wooden strut bracing the interferometer against the simulator super-structure succeeded in eliminating the offending mode. A more elegant solution will follow soon...

Next it was time to remove the CGH so that the M4/M5 wavefront test gear could go back into the hole in M3.

The little baffle suspended between M2 & M3 (aka Blackbeard's Patch) also had to come out before the long tube could be pushed up into place.

With the M4/M5 wavefront test ready to go again, Darragh could at last get back to some artificial observational astronomy - chasing pinhole images around to characterise the system before the M4 interventions scheduled for tomorrow...

2 years since his last IQ-related visit, we're joined by the chief engineer from SALT North for the next 2 weeks - welcome back John!

CO2 snow & a midnight raid on the gym

Extremely cool to get to see the primary mirror cleaning system in action today! A huge arm with a nozzle attached swings over the array, blasting CO2 snow over the segments.

I also relished the chance to play with a fisheye lens again, what a treat :) Note the plume of CO2 just to the left of the centre of the array.

Back in the clean room, Eben & James had finished installing the framework for attaching the dial gauges & LVDTs to the SAC.

We also spent time testing a new setup for measuring the reflectivity of M5. This involved shining a red laser down through the hole in the super-structure platform & getting the return to land on a photodiode mounted next to it. The effect of the laser hitting M4 along the way is shown below - the translucent gold-coloured Zerodur that the mirrors are made of lights up beautifully!

Further effort went into adjusting the CGH fringes obtained with the interferometer...

The incredible sensitivity of the interferometer's essential to us, but being capable of measuring to fractions of a wavelength of light also has its drawbacks! The system easily registers the disturbance caused by a car driving up towards the plateau, let alone the effects that pumps, fans, people & wind have on the building.

We decided that more weight on the NRS simulator might help damp out some of the jittering so a posse rushed down to the gym & made off with all the weights. The poor little bakkie barely made it back up the hill again...

Other than the exhausting amounts of pool being played, this was the most exercise we've had in a month. It added a whole new dimension to Clean Room Olympics, but alas did little to stabilize the fringes.

That's it for now - we're heading back to Cape Town tomorrow for a much needed recharge, tune in again when we return on 1 June!