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Axicon Centering Station

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.

Case Studies & Testimonials

  • How small can the PSM be used for centering on a cylindrical axis?

    The PSM is an ideal tool for finding the center of curvature of a ball or the axis of a cylinder. The question is for how small a ball or cylinder can the PSM do this?

    The smallest article that was readily available was a piece of monofilament 8 pound test fishing line that was 290 μm in diameter. There was no problem finding the axis of the fishline, and separating the Cat’s eye reflection from the surface from the confocal reflection of the axis. The experiment was done with a 5x objective, and the result would have been even more definitive using a 10x objective.

  • Why is proper alignment so important?

    Here is a case of a very happy customer due to better optics.

    A few days ago an astronomer friend of mine commented that he had gotten the optics of his telescope improved and the improvement reduced the time it took to get data by a factor of 3. For an astronomer this is a dramatic improvement since observing time on large telescopes can cost thousands of dollars an hour.

    My friend did not say how the optics had been improved, but the important point is that better optics, whether due to figure errors, mounting or alignment mean more productive optics. I generally think of better optics as a better product leaving the manufacturing facility without thinking about how much the better optics mean to the productivity of the customer.