--> dry nitrogen flushing through Taurus,
--> remote control for Z-coarse offset,
--> remote switch for deuterium lamp connected,
How do I balance the etalons?
Go out to Cass cage and put etalon into light table with pupil 8
in light table as well. This is the first thing that meets you when
you enter the Cass cage. Screw on the Ne lamp after opening top
and bottom windows.
At the s/w level, there are 6 etalon ports, with 3 and 6 clear. Put
your etalon in 1, 2, 4, or 5, and then drive this etalon to the
access port (light table) using the SMS control window.
(i) power up s/w control and select etalon then external=off
(ii) switch to R balance, balance needles using R control
(iii) switch to error signal, time const highest 1.6ms, gain lowest at 1
(iv) balance all needles with the coarse/fine control. Since the
etalon is not servo'd, the needle will flick through zero. Just get the
needles near zero using the controls. Some etalons are not able to be
balanced but will still servo at the appropriate positions.
(v) change time const 250ms and gain of 32 (loop is open here)
(vi) close loop and integrate
(vii) if loop overloads, reduce gain setting
(viii) optimize by eye
(ix) external = on, and away we go.
What causes large etalon oscillations?
(i) incorrect gain or time constant
(ii) large unbalanced R offsets
(iii) open or short-circuited etalon connector
How do we test that the shuffling is working o.k.?
--> For TTF, turn on CuAr or Ne lamp depending on filter; for other
etalons, turn on D lamp. These are chimney lamps and do not the
--> set pupil = 8
--> set aperture = 3 (thin slit)
--> put an etalon in the beam
--> You will need a blocking filter in the focal plane whose
width will depend on the etalon gap. If TTF, use one of the TTF
filters, say 670 (Ne lamp) or 710 (CuAr lamp). The UNC 19um requires a 45A blocker, say
the H-alpha filter. The 125um and 200um etalons require something
narrower than 10A, preferably at H-alpha. If not available, just
recognize that there will be order confusion in the output spectrum
creating more lines than you would expect.
We will now initiate an 80-step shuffle where the TTF is stepped
through 80 unique plate spacings, and the slit image is shifted
down the CCD 80 times.