Background
The DEIMOS grating tilt stages have a named position called
Zeroth_Order which is appropriate for zeroth order
imaging, a mode commonly used for aligning slitmasks. This
document describes the procedure for measuring the zeroth
order imaging position and updating the value in the DEIMOS
software.
Measuring the Zeroth Order Angle
The zeroth order angle must be chosen such that it places the
image entirely on the detector, but is not so close to the
limit of travel that you risk running into the limit (or, more
likely, violating the software limit and thus being unable to
start the move). As of 2016, the appropriate values
for the stages are as follows:
| Slider |
Limit of travel |
Zeroth order position |
| G#TLTVAL |
G#TLTRAW |
G#TLTVAL |
G#TLTRAW |
| 3 |
-18.438 |
-78300 |
-18.300 |
-78212 |
| 4 |
-18.491 |
-91600 |
-18.276 |
-90967 |
Invoking the Zeroth Order Position
Since the zeroth order position is a named position for the
grating tilt stages, one can command the stage to move to the
zeroth order position by setting the GxTLTNAM
keyword to the special value Zeroth_Order as
follows:
- modify -s deimot G3TLTNAM=Zeroth_Order
Changing the Zeroth Order Position
On October 2016 we measured the Zeroth order positions for
Slider 3 and Slider 4. Slider 3 was loaded with grating 600ZD
and Slider 4 with 900ZD.