Expansion of high tech materials
Thermally stable materials play an important role in dimensional metrology and in precision manufacturing. The currently highest requirements on the thermal stability of critical components are made in EUV lithography of reflection masks and mirrors. These are, therefore, based on substrates made of high tech glass/ceramics which are to exhibit a very low thermal expansion coefficient a (a
For the precise characterization of gauge-blockshaped measuring objects made of high tech materials, a precision interferometer was developed with the aim of measuring samples of up to 400 mm length with uncertainties in the sub-nanometer range. From such exact measurements of length, it is possible to calculate the thermal expansion coefficient as a function of the temperature with uncertainties of up to 2 • 10–10 • K–1. Furthermore, it is possible to get quantitative statements regarding the homogeneity of the thermal expansion, compressibility, length relaxations and also the long-term stability of samples.
Length measurements with sub-nm uncertainties demand, besides the application of frequencystabilized lasers, the consideration of influences whose uncertainty contributions are difficult to minimize. For this purpose, various methods have been developed in the PTB in the last few years and these have been integrated into the measuring process. A new autocollimation process is cited as an example and this ensures that the lightwaves reach the surfaces of the measuring objects exactly perpendicularly. The so-called cosine error is hereby lowered to under 10–11 • L. Furthermore during the electronic evaluation of the interference pattern, the exact assignment of the sample position to the camera pixel coordinates is considered. This is particularly important when it comes to measuring objects whose end faces are non-parallel and when the influence of small temperature-induced changes of the lateral sample position can be corrected. By taking the temperature-related influence of the deflection of the end plate wrung to the back into consideration, the precision could be increased further. When taking thermal expansion measurements on typical samples, length measurement uncertainties of 0.25 nm are now achieved.
In a recently completed international comparison measurement, the leading position of the PTB in the determination of thermal expansion coefficients was confirmed. The new possibilities for the precise characterization of high tech materials are already being used intensively by companies working in the fields of optics and precision manufacturing.
This text in the latest issue of PTB-news (08.2):
Dr. Rene Schödel, PTB Working Group 5.44 Interferometry on Prismatic Bodies, Phone (0531) 592-5440, e-mail: email@example.com
All news from this category: Physics and Astronomy
This area deals with the fundamental laws and building blocks of nature and how they interact, the properties and the behavior of matter, and research into space and time and their structures.
innovations-report provides in-depth reports and articles on subjects such as astrophysics, laser technologies, nuclear, quantum, particle and solid-state physics, nanotechnologies, planetary research and findings (Mars, Venus) and developments related to the Hubble Telescope.
Bringing atoms to a standstill: NIST miniaturizes laser cooling
It’s cool to be small. Scientists at the National Institute of Standards and Technology (NIST) have miniaturized the optical components required to cool atoms down to a few thousandths of…
Record-breaking laser link could help us test whether Einstein was right
Scientists from the International Centre for Radio Astronomy Research (ICRAR) and The University of Western Australia (UWA) have set a world record for the most stable transmission of a laser signal through…
Adaptive optics with cascading corrective elements
A cascaded dual deformable phase plate wavefront modulator enables direct AO integration with existing microscopes–doubling the aberration correction range and greatly improving image quality. Microscopy is the workhorse of contemporary…