Compensator Method for measuring of stress in glass

Home Methods Senarmont Lambda Plate Fringes

Set-up with compensator
First polariser at 45 degrees with the main stress axis Sample which gives difference in phase Compensator Analyser at minus 45 degrees with the main stress axis

The inserted compensator compensates at a defined way for the phase shift in the sample. The phase-shift of the compensator is changed till the intensity behind the analyser is zero, this is when the total phase-shift is zero. Then the phase-shift in the sample is opposite to the phase-shift which is set in the compensator, so can be read from the compensator. The light vectors at the different stages are:

After polariser at +45:

EyA = sin( w t)
ExA = sin( w t)
After Sample

EyB = sin( w t)
ExB = sin( w t + f )
After Compensator:

EyC = sin( w t)
ExC = sin( w t)
After Analyser at -45:

EyD = 0
ExD = 0


This method can be automated. For this, the light through the sample is sampled with a camera connected to a computer. Some special hardware has to be used: Measurements are done with different values for the additional phase-shift. Out of these measurements the value for the phase-shift (which should give the minimum light intensity of zero) is computed.