Axicon Centering Station
OPG has stopped offering a centering station using a rotary table to establish an axis in space to which to align optical system. Rather we now offer a centering station that uses an Axicon grating to create the axis.
Forthcoming papers will explain how the axicon grating creates the axis and how its position is probed with the PSM. The PSM is first aligned to the grating in reflection, then the source behind the grating is aligned to the PSM in transmission. Then the PSM is set to the height of a conjugate of the first lens to be aligned, and again aligned to the grating at that that height.
This means that any misalignment or lack of straightness in the vertical column is corrected prior to aligning the first lens. Once the lens is inserted 2 spot images will be seen by the PSM, one from the conjugate in reflection and the other from the grating in transmission. Once the 2 spot images are brought into coincidence on the crosshair of the PSM the lens is aligned in both tilt and decenter, and the original orientation of the axis is re-established ready to be used for aligning the next lens. The PSM is moved to a conjugate of the next lens to be aligned and the process repeated.
The advantage of this method over using a rotary table is that it is simpler in that there is no rotary table, everything sits still, and the alignment is a simple x-y motion without having to move the PSM vertically to find the 2 lens centers of curvature. The Axicon centering station also offers a simple way of fixturing the components being centered by means of vacuum. Because nothing is rotating the vacuum feed is easy to implement.