Axicon Centering Station

Precision centering stations, instruments for aligning lenses in a barrel and cementing lens groups, create axes in space used for centering lenses. A precision rotary table usually creates this axis. The Axicon Centering Station (ACS) uses an Axicon grating to create the alignment axis, instead. Because of the unique characteristics of the axis, a Bessel beam created by the grating, the task of centering is greatly simplified and the centering station hardware is less complex and expensive.

A spherical wavefront coming from a point source of light on the Axicon grating axis produces a slender light beam normal to the center of the grating that continues to propagate beyond the grating and another beam that reflects back from the grating toward the source. An autostigmatic microscope such as the Point Source Microscope (PSM) complements the Axicon grating as both the source of light to illuminate the grating and to detect the reflected beam. With the PSM aligned to the grating, a second point source of light behind the grating creates a second beam that propagates toward the PSM. The PSM aligns the second source to the grating so there are both co-axial reflected and transmitted beams entering the PSM. This completes the alignment of the centering station.

When a lens is placed between the grating and PSM, these two beams align the lens in both tilt and decenter to less than 1 μm and a few seconds of arc. If the two beams are coincident and centered on the crosshairs in the PSM it shows precise lens alignment to the grating axis. Because the aligned lens restores the light beams to where they were before introducing the lens, the beams align the PSM at a new vertical height prior to adding a new lens to the assembly.

Optical Perspectives supplies the ACS with a PSM having a 10x objective and computer to control the PSM and ACS, a motorized vertical stage with height resolution of 1 μm, a 75 mm square Axicon grating, 2 separately controlled laser diode light sources, a vacuum system for holding lenses and assemblies in place and a breadboard platform for flexible arrangement of assembly hardware. This is the standard ACS but custom modifications are readily available.