Techniques
Phase mode
Base on phase shifting interferometry, the fringes are shifted in Z, (commonly using a PZT), to produce several images to be able to calculate the phase difference for each point. The resolution of this mode is a fraction of the wavelenght used ( about 1 nm)
Wave mode
The wave mode is quite similar to the phase mode but it shift over a wider range of Z and calculate an order for each Z steps. This mode remove ambiguities related to finge disruption over the image. The resolution is identical to the phase mode
Confocal mode
Technique using the modulation of interference fringes produced by an optical signal coupled with a vertical scan. This technique makes it possible to obtain a resolution in Z close to a fraction of the wavelength used (ie approximately 10 nm) over a depth of several tens of microns. The zone measured is in the form of a surface which varies from a few hundred microns to a square millimeter depending on the objective used.