The flat is a Thorlabs dielectric coated mirror that is 6 mm thick. I bored the 5/32 inch hole myself with a diamond drill. This is quite easy to do.
Simply mount the mirror face down on another small piece of glass with optical pitch and bore the hole from the back side while immersed in water.
After drilling carefully clean off ALL the drilling debris and then heat up the assembly and carefully float the mirror to the edge of the glass plate and off, then clean up with acetone.
Dielectric coatings (or protected aluminum coatings) are rugged enough to survive this treatmentt undamaged.
The star image is guided quite accurately in the middle of the slit which produces a Gaussian profile centred on the 75um width. Isis handles this just fine.
However it is another story for the tungsten flats.
Here is the profile for my flat in order 32. Notice the increased noise near the peak of the blaze, right where you would expect less noise!
If I generate a profile in MaximDL from the straightened image of the flat for order 32 it is smooth, as it should be.
However, If I narrow the zone over which MaximDL averages then the profile starts to look like it does in ISIS.
I believe this shows that Isis is not quite capturing the whole 75um line width. This makes sense as ISIS was designed with a 50um fiber in mind.
This problem does not impact the star spectra directly because the gausian star profile has fallen off significantly towards the ends of the short slit.
It does, however, affect the accuracy of the blaze function that is generated from the tungsten flats.
Christian - if you are reading this I would be very grateful if you could add to ISIS an option to specify a slightly wider zone over which to integrate.
The reflective aperture was the hardest part for me to source. I had to wait over a year for it. It was made as a favour by the Nanofabrication Lab at our national research facility.
I can NOT ask for them to make another one with a shorter aperture.
Tim
