Objectives

• Microstructure surface characterization, testing non-homogeneous distribution of optical characteristics of objects in transmitted and reflected light.
• Measurement of diffuse objects.
• Advanced methods for measurement of dynamic stress and vibration.
• Detection of cracks. 

Principle

Heterodyne interferometry is based on the precise detection of the beat frequency between beams of two optical wavelengths. If one of two interfering waves is phase-shifted, the beat frequency undergoes the same amount of shift. Measuring it one extracts either the optical path difference or the phase anisotropy. The phase of the beat frequency signal can be measured with the accuracy better than 0.01 degree providing the most accurate interferometry technique available.

Advantages

• Ultimate accuracy and sensitivity;
• High noise immunity;
• Easy data processing as the beat frequency lies in the radio range.

Applications

Crack detection in Si wafers
Study on electro- and magneto-optical effects in materials
Vibration detection
Capillary blood flow monitoring in vivo by speckle interferometry
Detecting characteristics of moving objects using speckle interferometry.

Contact

Dr. Valery Gudelev
Phone              +375 17 284 17 00
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Application of near-IR heterodyne interferometry for crack detection in polycrystalline Si wafers used for solar cells manufacturing; a), b) – wafer images; c) phase anisotropy map demonstrateing the presence of microcracks of a 35-100 micron size.