Sunday, September 15, 2013

Echellograms Wherever You Look!

First things first - Ockert introduced Ray to the SALT coffee machine's Standard Operating Procedure!

He was also provided with the mandatory clean-suit & silly head-gear before getting to check on the progress being made inside the tank.

The main task for the day was to complete the alignment of the optics & so the LR mode fibres were opened up & brightly illuminated with a halogen lamp.  The light emerges through the open shutter on the left in the pic below & heads for the collimator mirror.

The collimator reflects the light towards the grating & produces an elliptical white patch on the échelle (the "white pupil" that defines this particular design).  This patch needs to be centred by adjusting the tip & tilt of the collimator mirror.  A screen placed at the dichroic shows where the resulting spectrum (diverging from the intermediate focus) lands & thus one can adjust the grating position to get the spectrum centred on the dichroic.

This all seemed way too quick & painless when we looked at the red camera barrel & immediately saw an échellogram on the front lens!  WOW :D :D :D

In fact, each other surface we then looked at showed the coloured orders in some form or other.  Presumably due to ghosting as light refects off the mirror-like CCD & travels back through the system...  Here's the blue pupil mirror showing the blue/green orders belonging to that channel.

Likewise on the blue channel's cross-disperser.

& the red/green orders on the red channel's fold mirror.

& on the corresponding VPHG.

Another blueward looking view...

Here's the échelle showing off its array of spectral ghosts.

Then looking through the dichroic towards the red pupil mirror.

& the surface of the red VPHG seen from a different angle.

As above, but focusing on a "deeper" layer of orders on the red VPHG.

This shot shows the MR, HS & HR mode fibres (left) being injected into the fore-optics - the image slicers are in the centre of the photo & L4 is on the right with the dichroic visible behind it.

With the grating aligned & no longer needing to be moved around, the brass counter-weight could be attached to the top of the cell.

So there we have it - the bench with all the main optics aligned! :)

The next job was to set up the optics that will feed the exposure meter.

The idea being to intercept the light coming from the exposure meter mirror (the thin, spherical strip that lurks in the gap between the two halves of the échelle mosaic) & direct it (by means of various lenses & mirrors) to the detector, a photo-multiplier tube that will attach to the outside of the tank.

As always, plenty of other work was going on outside the tank, including David doing the necessary surgery to repair the collimator mirror's damaged temperature sensor.

& more cabling & softwaring & FIF preparations & discussions about the tasks & tests that lie ahead.

Please note that we do Not need to mention the rugby this morning... thank you :(

1 comment:

  1. I'm sure David's hair wasn't as grey as that when he started HRS... ;-)