S e t - U p

Preliminary checks:

    --> 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 secondary mirror.

    --> 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.

In the CCD window, you can always return to normal mode to do a glance, say, with "method default". Probably best to do this after every shuffle since bombing in shuffle mode is not good. "Method shuffle" gets you back after "method default".

-- Notes by JBH (16/10/97)

Maintained by Heath Jones