Four articles explain the understanding of birefringence and the measurement principles and features of our equipment.

1. Basics of Birefringence Measurement
2. Measurement principle of Birefringence Measurement System PA/WPA series.
3. Basic Structure of the Systems & Measurement Examples
4. Range Limitation and its Extension by WPA Series

Basic Structure 

①Acquisition of state of polarization over light source　　　②Acquisition of state of polarization with sample

③Birefringence (phase shift & axis orientation) at each point by comparison of the states of polarization

Why using circular polarizer film:
If we used a linear polarizer, the regions of the sample having the same axis orientation as the film would not be correctly evaluated (no sensitivity).
Circular polarizer film allows to obtain the same sensitivity to birefringence independently from axis orientation.

Actual system picture

PA System : Measurement Example (1)

Plastic Molded Lens:
Distribution of Axis Orientation

Optical quality glass : phase shift distribution

PA System : Measurement Example (2)

PA Series include a model for microscopic applications, enabling evaluation of very small samples.

PA System : Measurement Example (3)

Plastic molded part (test piece) : evaluation of the differences between materials

Differences of material & molding parameters appear clearly as differences in the birefringence profile.

Phase shift along transversal line

※PC actually has the highest distortion. However, the phase difference is too large for the PA series to be measured correctly.

Range limitations of PA Series systems

The maximum birefringence that can be measured by PA system is λ/4.
Samples exhibiting greater retardation will be displayed with wrapped around values.

Evolution of recorded retardation for growing applied force on test piece (photo-elastic)

Values over ¼ of operating wavelength (520nm) are wrapped around.
It can result in ripples that do not exist in reality.

PA Series is limited to the evaluation of samples of less than 100nm of birefringence.

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