The Nexview interferometer layout
The Zygo surface profilers use interferometers built into the microscope objectives, in either a Michelson (left) or Mirau (right) configuration.
The objectives are calibrated so that the point of zero optical path difference (zero OPD) is the same as the focal distance, i.e., the distance from the beamsplitter to the reference surface is the same as the focal length. This means fringes will appear when the test part is in focus. You will hear working distance, focal distance, and zero OPD used interchangeably during training.
Breaking the Instrument
Optical profilometry is a non-contact imaging technique. The only way to break the instrument is to:
- drive any of the objectives into your sample (odd shaped samples must watch out for all the objectives on the turret!).
- make contact with the objectives on the turret while loading or manipulating your sample. All contact is bad, even the slightest bump or brush.
- change objectives without raising Z, allowing clearance for torrent rotation. The objectives on the turret are not parfocal, You must raise Z in order to change lenses.