Concept of an In-Plane Displacement Sensor Based on Grating Interferometry with a Stepwise Change of Sensitivity

Area of Science:

• Optical Metrology
• Solid Mechanics

Background:

• Grating Interferometry, also known as High Sensitivity Moiré Interferometry, is a technique for measuring in-plane displacement and strain.
• The sensitivity is typically determined by the spatial frequency of the specimen grating, with 1200 lines/mm yielding a basic sensitivity of 0.417 µm/fringe.

Purpose of the Study:

• To introduce a concept for an in-plane displacement sensor with stepwise adjustable sensitivity.
• To demonstrate how varying grating spatial frequencies can modify measurement parameters.

Main Methods:

• Utilizing a specimen grating with lower spatial frequency to access higher diffraction orders.
• Implementing a specialized filtration method to select desired diffraction orders.
• Employing an achromatic configuration with an illumination grating for vibration stability.

Main Results:

• The developed sensor allows for selectable sensitivities of 1.25 µm, 0.625 µm, or 0.417 µm per fringe.
• Correspondingly, the measurement range can be adjusted to approximately 600 µm, 300 µm, or 200 µm.
• The achromatic configuration ensures low sensitivity to environmental vibrations.

Conclusions:

• A versatile in-plane displacement sensor based on Grating Interferometry is demonstrated.
• The sensor's adjustable sensitivity and range cater to diverse experimental requirements.
• The method offers a practical approach for precise displacement and strain measurements in various applications.