April 2017 Newsletter
As I explained two months ago about the licensing agreement with Trioptics-USA to manufacture and sell the Point Source Microscope (PSM) and MicroFinish Topographer (MFT), this gives me time to develop new applications for both instruments and to consult on applying those applications. I am pleased to say that the applications spawned by customer inquiries and my own curiosity have led to four papers that will be presented this summer and fall. See the March Newsletter for the venues, titles and abstracts of the papers.
A major insight to several of these applications is that the PSM can probe custom computer generated holograms to find precise points in space to the micrometer level so that it is possible to design and fabricate a photomask with a volume array of precisely located points. These points can be designed as centers of balls that can then be cemented to the CGH to turn it into a jig or fixture for assembly of mechanical and optical components, or it can be used as a calibration artifact for precision instruments and machine tools. The PSM can locate the point to < 1 μm in a plane parallel to the CGH and to +/- 3 μm perpendicular to the CGH.
We have already demonstrated that you can, for example, cement doublet lenses without the need for a rotary table; the CGH establishes the locations of the centers of curvature of each of the surfaces to a common point so centering can be monitored at each step of the cementing process without having to move the PSM once it is initially positioned relative to the CGH.
With the help of Prof. John Ziegert at UNC-Charlotte and one of his students, we have done an initial demonstration of using a CGH to check the performance of a CNC multi-axis mill by placing the CGH on the work table and suspending a PSM in the tool spindle. Based on the initial success of these experiments, further investigations will take place this summer and be reported on in the fall.
Another area of investigation is using the PSM and a rotary table to find the optical axis of aspheric surfaces by recognizing that the optical axis is the line joining the center of curvature of the vertex sphere and the sagittal focus at an arbitrary zonal height. This requires two PSM’s, one looking on axis and one looking normal to the surface near the edge of the clear aperture for greatest sensitivity. It is easy to determine these two points on the optical axis to < 1 μm so the decenter can be certain to 1 μm while the tilt of the surface depends on the asphericity that in turn determines the distance between the center of curvature of the vertex, or paraxial, sphere and the sagittal focus.
Not only can the optical axis of the upper surface of an aspheric lens be found this way, but once it is found and adjusted so its optical axis is coincident with the rotary table axis, the second surface of the lens can be checked for centration without having to turn the lens over to check the second side. If the second side of the lens is plano or spherical, this measurement can be made by simply refocusing the on-axis PSM.
If the second side is also aspheric, the second PSM also has to be re-adjusted to locate the sagittal focus of the second side. As nearly as we can see from our initial investigation this method of centering aspheric surfaces seems to work for almost any lens configuration with the proviso that there must be sufficient asphericity that there is a reasonable separation between the two foci.
We are also glad to report that since we published a bibliography of research papers that mention the PSM in their work, another 9 papers were published in the last year. The titles and citations have been added to the current list at the top so the most recent are easily found. The PSM seems to find its greatest reported use in the alignment and assembly of astronomical instruments. This is not surprising because there is generally nothing proprietary about astronomical instruments and astronomers like to have their work recognized.
But it seems to us that this is just the tip of the iceberg since there are many PSM’s being used in industry but a combination of the need to keep certain applications proprietary and that there is no pressure in industry to publish. To say the least, we are gratified the astronomy community has found the PSM so useful in their work and that many have seen fit to mention their use of the PSM.
If anyone is interested in initial findings about our research into new applications of the PSM, just use the contact us email form and tell us your area of interest and we will be glad to forward our results to date so you may see if the PSM can improve your products or research.