The NGXO (Next Generation X-Ray Optics) project has several problems relating to how to bond a very thin glass mirror to a metallic structure without distortion. One problem is that all epoxies shrink (at the micron level) when they cure. This shrinkage distorts the optical quality of the mirror unacceptably. Another problem is how to correlate finite element models of thin glass mirrors to verify that they are accurately predicting the distortions that a real glass will see due to enforced displacements, such as those applied by epoxy shrinkage. The forces required to simulate epoxy shrinkage and to balance a mirror on a bed of actuators are in the 100-1000 micro-newton range. The displacements are on the order of a few microns. These tiny forces and displacements cannot be easily measured or actuated with typical lab equipment.

A nanoprobe capable of movement in the nanometer range and simultaneous force measurement in the milli-Newton range has been created. This device has applications in optical systems where very small distortions are desired along with a measurement of the forces necessary to create such distortions. A collection of such devices allows a new way for mirrors — especially thin mirrors — to be held without distortion by controlling the force supporting the mirror via adjustments to the nano-actuators. Another application is an apparatus for correlating finite element and optical ray-trace models.

A known force in the milli-newton range is applied to a thin mirror, and the distortion is measured with an interferometer and compared to predicted finite element distortions. The force sensor has a range of ~30 mN and resolution of ~.01 mN. The nano-actuator has 30-nm resolution, 12.5-mm travel, 0.2-mm/s top speed, and 50N max force. The force sensor is attached to the nano-actuator shaft so that the sensor tip becomes the tip of the nano-actuator. Both devices are linked together and controlled in LabVIEW software. The unique feature of this device is that for the first time, it is possible to push on something with known micro-newton or milli-newton forces, and/or displace something and measure the resulting force.

This work was done by David Robinson, Ryan McClelland, and William Zhang of Goddard Space Flight Center. NASA is seeking partners to further develop this technology through joint cooperative research and development. For more information about this technology and to explore opportunities, please contact Scott Leonardi at This email address is being protected from spambots. You need JavaScript enabled to view it.. GSC-16061-1

NASA Tech Briefs Magazine

This article first appeared in the June, 2016 issue of NASA Tech Briefs Magazine.

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