Flip Mirror Shim/Alignment

(a)

This post shows the EXES alignment in medium res mode. I measured the position of the beam on the echelle paraboloid and the detector plane using paper screens in order to select the best angle for the flip mirror in lo-med mode.

For the alignment on the echelle paraboloid mirror, we are interested in having the input beam and the dispersed beam hit the mirror in a line along the long axis of the paraboloid mirror.  According to the optical design, the input and dispersed beams should each be +/-20mm from the midpoint of the long axis of the paraboloid mirror.

We also would like the beams to hit close to the center of the mirror along the short axis of the paraboloid, but this is a secondary concern to the having the beam at the detector centered in the echelle-echelon direction as well as the input and dispersed beams in a line,  with a separation of 20mm each from the center of the paraboloid long axis (as described in the previous paragraph).

(b)

To help in this alignment I made a screen of card stock and grid paper, and taped it to the side edges of the paraboloid mirror. The mirror dimensions are 7.5”x5”. I marked the center along the short axis at 2.5” from either long edge of the mirror.

Along the long axis, I marked the midpoint at 3.75”, as well as parallel lines at +20mm and -20mm to this line, where the input and dispersed beams should hit.

I also made a screen of tissue paper and cellophane and placed it over the output beam position just before the detector focus.

OK, so that’s the context.

The status now is that we have the input and dispersed beams hitting the paraboloid along the center long axis line. The input beam is about 5mm from the position where it should be along the long axis (it should be at 20mm toward the fore-optics side and it is at 15mm). I will readjust the flip mirror stop to change this position.

(c)

Figure (a) shows the target on the echelle paraboloid. It has flaps cut into it so that we can measure the positions where the beams hit the mirror, and then when the flap is pulled back we can see the beam after it reflects from the mirror.

In Figure (b) the beam has been stopped down to about 0.5” and the input beam, coming from the flip mirror is shown. As meantioned it should be about 5mm farther away from the viewer, but this will be fixed by readjusting the flip mirror stop.

In Figure (c)  the dispersed beam is shown. It falls in a line with the input beam because of the flip mirror shimming and the adjustment of the dispersion screw on the parabolloid.

In figure (d), the beam position at the detector is shown. The cutout in the note card is slightly misleading. The center of the detector in the ruler long axis is located at 0.75” along the ruler. As a consequence of the flip mirror shimming and the steering of the parabolloid, the beam hits about 2/16” to the left of the center.

(d)