Friday, September 13, 2013

Surviving Friday the 13th...

Sorry to have missed Shireen's farewell in Cape Town today  - we miss you already S!  & Big Up to Luke for spending the day in the car to fetch Ray, allowing me to stay here for the start of the optical alignment process...

While Luke set off for CT, Tech Ops brought the Atmospheric Dispersion Compensator (ADC) down so that Janus could check it out & fix whatever's wrong with it.  This needs to happen before we can install the Fibre Instrument Feed (FIF) & the HRS auto-guider as the ADC can't be taken out while the FIF's in.

Over in the next room, David got the blue camera of Her Royal Spectrographness hooked up to the vacuum pump to get it ready for action.

While Jürgen opened up the Medium Resolution (MR) mode fibres in order to get the fore-optics lined up. 

Having done all this before, he knew where the light should land on the collimator so that it'll reach the dichroic after hitting the grating (once the whole system's aligned).  Thus the bridge holding the fore-optics could be adjusted horizontally & then clamped in place, while the vertical alignment relied on positioning a shim underneath the bridge.

The six fibres for the three sliced modes (MR, HS & HR) were then set up & illuminated so that we could inspect the sliced images formed by the fore-optics.

We needed to set up a camera (the small grey box near the centre of the photo) near the focus to view the sliced images.

Here's the video output from the camera, showing the three sliced modes: HR, HS & MR (from left to right).  This image is rotated 90° as the camera was mounted on its side.

The next task was to install "the tower" - the complicated assembly that carries the mode selection drive, the slit-mask, the shutter, the calibration fibre & the LR fibre outputs.

This shows the slit-mask for the MR, HS & HR modes (from top to bottom) with its vertical & horizontal adjusters visible to the left & below the mask.  The mask needs to be aligned with the images formed by the fore-optics to eliminate any stray light arising within the slicer optics.

With the tower in position, all 8 fibres illuminated & the shutter open, one can see all the outputs & then adjust the slit-mask to line up with the images for the 3 sliced modes.  The (unsliced) LR mode outputs are to the left of the sliced ones.

From left to right in the pic below you see the fore-optics, the tower & the camera that was used to get those 2 sub-systems lined up.

Next to go onto the tower was the mode-selection drive & the shutter assembly.  A nifty eccentric cam system moves the mode selection slot up & down to isolate the desired mode.

On the other side of the mode selection drive is the shutter.  

This fiddly bit gave us some trouble as it refused to open.  We tried the spare shutter & had the same problem, so then swapped to the spare controller & then both the shutters (the spare & the original) worked...

Eddy could then drive the mode selection mask & the shutter from his software running in the electronics room.

Here you can see the mode selection mask (set to the LR mode) through the open shutter.

The Jürgemeister's next trick was to set up a laser over near the collimator so that he could roughly check the alignment of the various elements.  A green laser's Perfect for the task as its wavelength (532 nm) is close enough to the dichroic's cross-over (~555 nm) for the light to be able to negotiate both the red & the blue channels!

Although parallax is a pain & it's tricky to dodge all the laser spots bouncing off the various surfaces, one can adjust the mirrors to get things into reasonable shape.

Green laser spots all over the show!

It's neat to compare photos taken without (left) & with (right) a flash...  The pics below show the green laser going through the blue channel, without any fuss in the shot on the left, but with the addition of red spots in the one on the right.  These spots are presumably the reflections of the bright flash, selectively thrown back at us by the coatings on the blue camera optics which are designed to reject red light.

This is good enough for today's rough pre-alignment, tune in tomorrow for the full treatment!  In the meantime - a big Welcome to HRS Boss Ray Sharples who'll be joining us up here for the next 3ish weeks :)

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