Interference microscope

A microscope that visualizes and measures differences in the phase of light transmitted through or reflected from specimens. The entering light is split into two beams that pass through the specimen and that are recombined in the image plane, allowing visualization of object details that are invisible with a single beam. The diffracted and non diffracted waves are not spatially separated, but light (the object beam) that passes through or is reflected from the object interferes with light (the reference beam) that passes through or is reflected from a different region of the specimen plane or is reflected from a comparison (reference) surface. For interference to be visible, the light beams must be coherent; in other words, the beams must maintain a constant relationship of wavelength, phase, and polarization over a relatively long period. The easiest way to achieve coherence is by using a device such as a semi reflecting mirror, which splits a light beam into two beams.

Random changes in the properties of successive photons from a given point in the source induced by moving the sample table with nanometer precision then affect both beams simultaneously. Differences in optical path introduced by various parts of the object can be seen as variations in intensity or color. The resulting interference patterns as a function of table movement are recalculated into a topographic pattern of the structured substrate under investigation. That way height information with sub-Ångstrom precision becomes available.

Specifications (Fogale Microsurf 3D)
  • Vertical measurement range 0.1 nm to 500 μm standard
  • Vertical resolution < 1Å
  • RMS repeatability 0.3 nm RMS
  • Lateral spatial sampling 0.17 μm to 3.2 μm (in standard)
  • Field of view 130 μm x100 μm, 2.5 mm x 1.9 mm
  • Reflectivity 1% to 100%
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