A broadband white-light LED, or xenon lamp, is used to illuminate the source

The light travels via optical fiber from the source via a fiber coupler to the interferometric probe

The interferometric probe consists of a sample arm and a fixed reference arm in a Michelson configuration

The reflectivity of the static mirror is matched to the reflectivity of the sample for maximum interference contrast 

A long pass filter can be added to remove blue light if measuring photoresist

The interfered light is reflected through the optical fiber via the coupler to a collimating lens that illuminates a volume holographic grating to form a spectrum on a linear CCD camera

The CCD camera generates a spectrum (Intensity versus Frequency) at up to 66 kHz

Real-time Fourier Transform of the spectrum (with appropriate bandpass filtering) results in the axial distance or thickness information used to locate the plane of each surface along the measuring distance of the interferometric probe

Mechanical scanning of the sample under the single-point probe results in a high-lateral resolution 4D (X,Y,Z,Thickness) surface topography and thickness point cloud data array