Normally I do not discuss my experience using a particular piece of opto-mechanical hardware such as this. In the case of this item, I decided to deviate from my normal practice and talk about this item and my own experiences, because I felt it might be useful to others who might benefit from this information.
I had an experimental application which needed a high-angular- resolution adjustable mirror mount which satisfied certain specs. Other mirror mounts to which I had access did not work for this experiment. I found this item via an on-line web search of Newport MKS products. To my surprise, it seemed that this device could satisfy my requirements for my experiment if I could believe their stated specifications. Although this device can hold a round mirror which is limited to 25.4 mm (one inch) in diameter and I would have preferred a larger mirror capacity, I decided to give this device a try because its other specs were compatible with my experiment.
Therefore, I purchased one of these mirror mounts and received it quickly since Newport had it in stock. Before continuing with my discussion, I should emphasize that I did buy this device like any other customer, and I have no other business relationship, nor any other sort of connection with Newport MKS at all. My “review” of this product is therefore unbiased, and of course it is based only on my personal experiences with one (1) specimen of a particular product from this supplier. A sample size of “one” certainly does not qualify as a valid statistical sample for testing and readers will hopefully understand my reluctance to assume that my experiences will apply to all of these devices. However, with that caveat, I will proceed.
I needed a mirror adjuster which would have the highest possible angular resolution, adjustment sensitivity of 2 seconds of arc, high stability, very good repeatability, and low thermal drift. This particular product seemed to suit my requirements. This Newport SX100-F3KN-254, 3-Knob Suprema XTE Kinematic Mount was described as “the highest performing mount in the Newport Suprema family, as a result of its new actuators, its materials, and its design configuration.” The part of its design which really appealed to me was the fact that it incorporates three (3) threaded screw actuators each of which has 254 threads per inch. After doing a somewhat cursory search on the web, this seemed to be the finest thread-cut for screw actuators which I found, at that time. The other good feature of this mount was its construction with stainless steel alloy giving it a 38% lower coefficient of thermal expansion (CTE) than aluminum mounts, per the manufacturer. The fact that it used a kinematic mounting support design with three screw adjusters having the same 254 TPI threads gave me the option of tilting the mirror in two orthogonal angle directions as well as translating it along its “z” axis direction, which in terms of translation, I did not need to do.
Some of the technical specs which the manufacturer stated are:
Kinematic mount mechanism
Optic Diameter = 25.4 mm
No. of Actuators = 3 with Knobs to adjust them
Screw Thread for Actuators = 254 TPI
Material = Stainless steel
Feature = Low CTE, (low thermal shift)
Angular Range = ± 7°
Sensitivity = 1.5 arc second
Bottom Support = Clearance hole for 8-32 screw is provided
The sensitivity spec was exactly what I was looking for. They added the comment that this spec is based on the assumption that the smallest possible manual angular adjustment which the user could make is a rotation of one degree of the adjuster screw knob, which sounded reasonable to me.
When the Suprema XTE Kinematic Mount arrived I inspected it visually and tried turning the adjuster screws. The manufacturer had stated elsewhere that in addition to the ultra-fine adjustment resolution of the 254 TPI screws, this mount had, (here I quote them exactly) “. . . the Suprema XTE mounts have consistent, smooth adjustability and feel, owing to the 3V kinematic configuration of the contact points. Because of the 2-point V-groove contact across each of the adjustment screws, the turning resistance is the same on each actuator.” They use polished carbide pads for those contacts. My observation agreed with their claim. The three screws turned very smoothly with what appeared to be identical resistance and there was no evidence of sticktion that I would find objectionable. They turned in either the CW or the CCW direction with the same ease. It seemed like the threads were lubricated with something but I did not investigate this.
For my application I would “push their operational specs to the limit.” I needed to adjust the one inch round mirror’s tilt in one direction only, but I wanted to be able to tilt that mirror from an arbitrary zero position by angles of 3 arc sec, 6 arc sec, 15 arc sec, and 30 arc sec. This would be done repeatedly for numerous trials, and I needed good repeatability between trials. It was not essential that the mirror could return to exactly the same zero position, as I could get around this. I knew I would not be able to do these tests unless I had some kind of reference method to help turn the screw knob through a known angle. But, I did not want to invest a lot of time or cost in preparing a superbly accurate method.
My compromise was to prepare a scale with a computer drawing program which had radial lines and tick marks indicating angles of 0°, 5°, 10°, 15°, and 20°, with added tick marks indicating half-way values between these. After printing this on paper I checked it with a draftsman’s protractor and found it to be good enough. I used some mechanical components I had in stock to make a pointer and attached it to the screw I was going to adjust. It attached directly to the adjuster screw shaft behind the knob so that it would not slip. I placed the scale on a card backing and attached it to the assembly with brackets I had in stock, almost touching the metal pointer which was made from precision micro-shaft material. This arrangement provided a means to rotate the adjuster screw by known angles (approximately of course) with unknown repeatability. Not a perfect solution; but I determined by experiments that this would work for my tests if I exercised some patience.
Proceeding with my planned experimental application, I used the Newport SX100-F3KN-254, 3-Knob Suprema XTE Kinematic Mount to tilt the 1 inch diameter mirror, and examined the results with a calibrated autocollimator capable of reading mirror tilts directly to 0.2 arc second. About 30 trials were made initially. These trials were aimed at becoming familiar with the operation of the mount and its added scale and pointer. (The autocollimator was known to work as advertised and to be accurate.) Further trials (about 50 over several days) were made in support of the experiment. The results do seem to confirm the specs given by Newport MKS for this device.
In short, it seems that an operator can make a change in the mirror angle as small as 1.5 arc sec with good reliability, if and probably only if they can be assured that the adjustment knob is rotated accurately through the chosen small angle. In my experiment it became obvious to me that what limited the accuracy of my results was not the performance of the kinematic mount, but definitely my ability to set the pointer on that shaft to the appropriate tick mark on my scale. My home-made scale was surely not a perfect rendition of what might be a professionally made scale.
An example data result from one of my tests is given here: A set of trials tilting a mirror surface by 15 seconds of arc from a common zero:
Theoretical value sought = 15.00 (sec)
Number of data values (trials) = 29
Mean value = 14.9532
Range = 0.8
Median value = 14.99
Modal value = 15.00
Standard deviation = 0.20889
After analysing this data, I “monkeyed” with the mount and autocollimator and verified that I could not set the pointer on the desired tick mark perfectly, and that was a clear error source. Also, the autocollimator is capable of reading a tilt angle directly to 0.2 arc sec, but recording data to two decimal places meant I was estimating the second decimal place.
My conclusion: The SX100-F3KN-254, 3-Knob Suprema XTE Kinematic Mount from Newport MKS is capable of doing what the manufacturer says it will do! The person using it will need to devise a method of accurately turning the adjuster knobs by a small incremental angle. Alternatively, the user can use a good autocollimator to optically measure the tilt angle that is produced by some uncalibrated adjustment of a knob. I rate this device as a very useful and reliable mount for small angle adjustments of a mirror, for applications where a 1” diameter mirror is suitable.
Thanks for reading. Do good work!
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Optics Lab Tips and Tricks 