Phase Shift Interferometry (PSI) is a high-precision optical technique used for areal surface characterization of super-smooth samples. It works by introducing controlled phase shifts between the reference and measurement wavefronts while recording a sequence of interferograms. Under controlled conditions, the optical phase distribution is reconstructed and converted into 3D surface topography with sub-nanometric vertical resolution.
Using monochromatic light sources, typically red, green, or blue LEDs, PSI can achieve vertical repeatability below 1 nanometer under optimized laboratory conditions. Its extreme phase sensitivity makes it ideal for detecting minute surface variations on optically smooth surfaces.
However, PSI is best suited for super-smooth, reflective surfaces, as it cannot accurately measure rough surfaces or large step heights.
HOW DOES PSI WORK?
The working principle of Phase Shifting Interferometry can be described through the following steps, which convert phase information into precise 3D surface topography:
Monochromatic illumination: A monochromatic light source (red, green, or blue) is directed into the interferometer.
Beam splitting: The light is divided into two paths: one directed to a reference mirror and the other to the sample surface.
Phase shifting: A controlled phase shift is introduced between the reference and measurement beams, typically using a piezoelectric actuator or mechanical modulation.
Interferogram acquisition: Multiple interferograms are recorded at known phase intervals.
Phase reconstruction: The collected data are analyzed to determine the optical phase distribution across the surface.
Topography calculation: The phase information is converted into height values, producing a 3D map of the surface with nanometric or sub-nanometric precision.
APPLICATIONS
Phase Shifting Interferometry is applied in areas requiring ultra-high precision surface measurement, including:
Optical component inspection: Characterization of polished lenses, mirrors, and coatings.
Semiconductor industry: Measurement of wafers, thin films, and microstructures at the nanometer scale.
Microelectronics: Evaluation of MEMS devices and flatness control of substrates.
Materials science: Analysis of super-smooth or reflective materials with sub-nanometric resolution.
Precision manufacturing: Quality control of ultra-polished surfaces and high-value components.
