IRTF Optical Alignment

After a long night of observing, Matt, Tommy, John and Andreas have concluded that we are losing a great deal of light at the slit.  This may be attributable to adjustments made inside EXES to compensate for astigmatism in our oBox powered mirrors, or possibly to a misalignment between the telescope optical axis and that of the instrument.

As a test, we'll start by placing our laser fiber at the expected telescope first focus, and looking at our beam as it traverses our foreoptics.  Placing both the end of the fiber and the center of our beam-defining iris at the design height of 4.162" above the optics plate, and centering both on the centerline of the optics plate, we se that the beam hits near the center of the ellipsoid, but is steered nearly off the hyperboloid and enters the window.  Here is the beam at the hyperboloid:

Admittedly hard to see, but the edge of the red laser beam is essentially coincident with the edge of the hyperboloid.  Because it is off-center on the hyperboloid, it enters the instrument window off center:

Again, kind of hard to see, but the spot is entirely in the upper left quadrant of the entrance window.  Suspect that this is not a good arrangement.

At his point we turned the laser/iris assembly around so that it shines toward the fold mirror.  It was *not* hitting it on center, be we decided to adjust the beam for level travel along the optics plate as we had for the Z-beam optics, and attribute the angle to manufacturing tolerances in the bracket.  We placed tissue paper across the fold mirror to define an edge that coincides with 4.162" above the optics plate:

The line between the tissue paper and the hand-held card is a 4.162" off the optics plate, and it pretty well splits the beam, suggesting that the laser beam is traveling parallel to the plate at the right height.  Whether this beam its the mirror at the same spot as the telescope central ray is the big question.  We should be able to translate and/or tilt the fold mirror to send the sky beam back along the right direction.  We'll need actual star light to verify this.