Limitations on the measurement of relaxation times using a pulsed Kerr effect method

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Abstract
Relaxation times may be measured by observation of the birefringence produced by the application of a pulsed electric field. A brief resumé is given of the methods of detection of the birefringence. These may be linear or quadratic according to whether the signal is proportional to the first or second power of the birefringence. A combination (quasi-linear) is also possible. Considerations of signal-to-noise ratio, current limitations of the detector system and signal distortion are fully treated. The analysis when two relaxation times are present simultaneously is given and it is shown that such a case may be confused with the results obtained with one relaxation time if the parameters are not fully known. Errors in the determination of relaxation times are examined. It is concluded that a linear detection method is preferable to a quadratic one because the signal-to-noise ratio and distortion tends to be less but these advantages do not occur when large bandwidths have to be used.