Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Fizeau interferometers for surfaces with different reflectivity

19.12.2007
Due to their stable design, Fizeau interferometers are used to determine the topography of surfaces such as, e.g., plane surfaces. PTB has now developed a method which makes it possible to analyse surfaces with different reflectivities in a simple way. This method can also be extended to dynamic measurements.

Fizeau interferometers generate an interference between the surface of a test sample and a reference surface that is brought close to the test sample. The interference image is recorded and analysed by an imaging optics system. The contrast and the shape of the interference signals depend, however, on the reflectivity of the test samples. The time and effort required for measuring and analysing the topographies of differently reflecting test pieces is therefore significantly increased.

The method of separating the wavefronts of the reference surface and the test sample surface in the plane of the reference surface – for which a patent has been applied for – uses a new generation of commercially available beam splitters, also called "on-axis beam splitters", which cause a separation of the polarisation directions of the incident light along the optical axis. In comparison with common Fizeau interferometers, this has various advantages. On the one hand, through the generation of polarised light, the measurement can be traced back to a pure two-beam interference. The analysis of the signal is thus significantly facilitated and improved. Classic Fizeau interferometers, however, are based on the analysis of the multiple-beam interference.

On the other hand, by varying the direction of polarisation, a maximum contrast can be set, independent of the reflectivity of the test sample. In contrast to this, in conventional Fizeau interferometers, different reference surfaces with adapted reflectivity must be held available in case the reflectivity of the test samples varies strongly.

In order to increase the accuracy of analysis of common Fizeau interferometers, a variable phase is generated by varying mechanically the distance between the test sample and the reference surface (phase-shifter interferometry). Another advantage of the new method is that such a phase shifting becomes possible through the use of electro-optical components and thus without using mobile parts. Thanks to the increased measuring dynamics achieved in this way, it is, for example, possible to carry out topographical measurements in environments which are subjected to vibrational strain.

The new method allows a facilitated and improved analysis of the measurement data, requires only one calibrated reference surface instead of several, and opens up new possibilities of application in the field of dynamic interferometry. It is particularly suited for measurements on structured or unstructured surfaces with different reflectivities – especially in the optical and semiconductor industry.

Erika Schow | alfa
Further information:
http://www.ptb.de

More articles from Physics and Astronomy:

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

nachricht What do Netflix, Google and planetary systems have in common?
02.12.2016 | University of Toronto

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>