Source and Optical Element Movement on Slit elements

[srio]

Bugs in OASYS / Shadow3, Jan 12, 2017 - Source and Optical Element Movement

Question by J. Dvorak. Answers in bold.

test: I set up a very simple geometric source, working in mm units using OASYS
point source, +H div = -H div = + V div = -V div = 0.001 rad, with a flat angular distribution
put a screen 1000 mm away, with a very short output plane, so that the OASYS plot shows the beam footprint at essentially the position of the screen

In this case, the beam footprint on the screen should appear as follows:

Test 1: Go under 'Optical Element Movement' and set it to 'Yes'
I find that none of the three translations or rotations have any effect.

It is normal. May be not logic. It has an explanation: the slit in ShadowOui, is in fact defined accompanying an “empty optical element” that you do not see in the interface. Moving an “empty element” does not make any effect.

Test 2: Go under 'Source Movement' and set it to 'Yes'. I set 'angle of incidence' to 0 (not quite sure what this does. angle relative to what?) and set the 'distance from OE' to +1000 mm. It is not explicitly stated in which reference frame this is, however, I assume this puts the source at -1000 mm in the OE reference frame, so I have reproduced the above configuration. I then get the same footprint on the screen as above.

It would be helpful if it explicitly says what reference frame the 'distance to OE' refers to.

The menu you refer to:

concerns the placement of the source (previous continuation plane) from the element itself. Therefore, in some way you should "copy" some information you already introduced (distance and incident angle).

Here there is a "complication" because you are using a slit as a testing element. In principle, one should use an optical element for that, with the referente frame as stated in the
Shadow3 primer

Therefore, you are applying the movements on an "empty element", and this is why you get weird effects. You should think in something like:

'z rotation' keeps image centered, but skews it. It acts like a rotation about the y axis. Furthermore, it does not act like a rotation of the source, it acts like a rotation of the OE reference frame.

in OE reference frame
x translation – seems to work correctly
y translation – should keep image centered, but make it larger or smaller, however, it acts as a z translation
z translation – acts like a y translation, making the image larger or smaller. Furthermore, if my interpretation of 'distance for OE' is correct, it has the
wrong sign. Moving +500 mm in the y direction in the OE reference frame should make the distance between the source and OE shorter,
and reduce the image size on the screen by 0.5 mm. It has the opposite effect.

in Source reference frame
x translation – seems to work correctly
y translation – in this very simple system, the +y direction in the source and OE reference frame are identical. In this case, if I set y offset to +500 mm,
the distance between the source and screen should decrease, and the image should be centered but smaller by 0.5 mm. This works correctly.
z translation – seems to work correctly

Please check the movements and you will see that it make sense now. I agree that is not trivial, the problem is that you have chosen a slit as your element, and we implemented it in ShadowOui linked to en empty element that you do not see. It is on top of this empty element that the movements are applied.