Fizeau interferometers for surfaces with different reflectivity

December 18, 2007

This release is also available in German.

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.
-end-


Physikalisch-Technische Bundesanstalt (PTB)

Related Surface Articles from Brightsurf:

3D printing the first ever biomimetic tongue surface
Scientists have created synthetic soft surfaces with tongue-like textures for the first time using 3D printing, opening new possibilities for testing oral processing properties of food, nutritional technologies, pharmaceutics and dry mouth therapies.

Surface waves can help nanostructured devices keep their cool
A research team led by The Institute of Industrial Science, The University of Tokyo demonstrated that hybrid surface waves called surface phonon-polaritons provide enhanced thermal conductivity in nanoscale membranes.

A novel salvinia-like slippery surface
Inspired by the hydrophobic leaves of Salvinia molesta and the slippery Nepenthes pitcher plants, a Salvinia-like slippery surface (SSS) consisting of protrusions with slippery heads was designed.

Illuminating cell surface receptors
Human cells sense and communicate via cell surface receptors on their surface.

Tuning the surface gives variations to metal foils
IBS researchers reported how to give variations to single crystalline metal foils.

Division of labour on the surface of bacteria
Bacteria of the species Thermus thermophilus possess two types of extensions on their surface (pili) for the purpose of motion and for capturing and absorbing DNA from their environment.

Changes in surface sugarlike molecules help cancer metastasize
Changes in a specific type of sugarlike molecule, or glycan, on the surface of cancer cells help them to spread into other tissues, according to researchers at UC Davis.

Journalism is an 'attack surface' for those who spread misinformation
For all the benefits in the expansion of the media landscape, we're still struggling with the spread of misinformation -- and the damage is especially worrisome when it comes to information about science and health.

Finding connections at the surface
How and where receptors touch at the surface of a cell may influence the strength of neuronal connections and contribute to identifying better medical interventions for pain, cancer other diseases.

A self-cleaning surface that repels even the deadliest superbugs
A team of researchers at McMaster University has developed a self-cleaning surface that can repel all forms of bacteria, preventing the transfer of antibiotic-resistant superbugs and other dangerous bacteria in settings ranging from hospitals to kitchens.

Read More: Surface News and Surface Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.