Imagine that the section of our OAP has been cut out of the parent parabola.  Now further imagine that this OAP is rotated so that it remains facing the focus point.  In fact, imagine that it is rotated in such a way that the parent parabola remains locked onto the focus point, and the parent parabola actually rotates around the OAP section, sort of like the hands of a clock rotate about the face.  This rotation is known as “clocking.” 



The animation above shows how the OAP, parent parabola, and focus point positions relate to one another as we perform this clocking rotation.

It helps to think of the parent parabola as an umbrella, where the focus point is like the handle of the umbrella, locked in place, and the OAP section is a small round patch at one edge of the umbrella, also locked in place.  With these two points locked down, the umbrella (the parent parabola) rotates eccentrically about as the OAP section is clocked.

In the Lens Data Editor, select Surfaces 11, 12, and 13 and then click on Tools | Coordinates | Tilt/Decenter Elements.  You can leave everything at their default values (I chose to change the Row Color, to help keep things organized) and click [OK]:

Make the “Tilt About Z” on our new Surface 11 a Variable:

We want to clock the OAP around until the output beam is parallel to the optical bench (the X-Z axis).  That means we want the output beam to have no directional component in the y-direction.  To do this, we will add a line to our Merit Function, with the Global Ray Y-Direction Cosine (RAGB) operand.  This simply measures the Y Direction Cosine of a ray. We want the Y Direction Cosine of our output ray (at Surface 17) to be exactly zero.  We’ll also add a few lines in the Merit Function to keep the Absolute Value (ABSO operand) of the parabola’s “Tilt About Z” (using the PMVA operand on Parameter 5 of Surface 11) less than 180 degrees (we’ll be using the “Operand Less Than,” or OPLT, operand to do this):

Now we optimize, same way as before.  Again, the Merit Function value should drop all the way down to 0.000000 in a matter of seconds.  Note that there are actually two equally good solutions for the value of “Tilt About Z” for the current example.  The two solutions have output collimated beams that go off in different X-directions along the table top.  For the current demonstration, we’re not concerned about which solution we get.  Because of this, when you optimize your design, you might end up with a different solution than I did, so your layout image may look slightly different than the one shown below.  Both solutions end up with the output beam coming off the parabola in a horizontal direction (parallel to the X-Z plane).

In addition to being decentered and tilted just right, our parabola is now clocked perfectly to produce a beam that is parallel to the surface of our optical bench.

Here is what the layout should look like at this point:

Finally, to make it look like an OAP instead of a full parabola, we can add a 4” diameter, decentered aperture to Surface 13:

Here’s our final layout:

Just for fun, I added an optical breadboard as a non-sequential object (aligned parallel to the x-z plane) in order to give a better perspective on the placement and orientation of the system, in the animation above. And,  to make sure everything is properly aligned, we take one last look at the spot diagram:

With that, the design, positioning, and clocking of our OAP is complete.  We finally need to determine the actual placement of the OAP relative to legacy optical system.