The coherent gradient sensor for thin film curvature measurements in multiple media

• The CGS system is investigated under multiple media, which can extend the CGS applications remarkably.
• The general calculation formula for curvatures are obtained.
• In case of two media, theoretical calculations are verified by experimental measurements.
• The system measurement error caused by wave length is presented.

The Coherent Gradient Sensor (CGS) system has many merits, such as full field, real time, nondestructive, vibration insensitivity, etc., which is developed to measure the curvatures and nonuniform curvatures changes of film-substrate systems in multiple media with different refractive indexes. The general calculation formula for the curvatures in multiple media are obtained. Take the CGS applied in two types of medium as an example, the presented theoretical analysis has been verified by experimental measurements when the specimen is immerged into water or silicone oil. Moreover, the influences of wave length on the measurement error of this system are reported.