Photoelasticity and Polarized Light Up to now we have treated the light field as a scalar quantity. The electromagnetic field, however, is a vector quantity which is perpendicular to the direction of propagation and with a defined orientation in space. This property is known as the polarization of light. In our treatments of interferometry and holography it is silently understood that the interfering waves have the same polarization. In practice, however, this condition is fulfilled to a greater or lesser degree | Optical Metrology. Kjell J. Gasvik Copyright 2002 John Wiley Sons Ltd. ISBN 0-470-84300-4 9 Photoelasticity and Polarized Light INTRODUCTION Up to now we have treated the light field as a scalar quantity. The electromagnetic field however is a vector quantity which is perpendicular to the direction of propagation and with a defined orientation in space. This property is known as the polarization of light. In our treatments of interferometry and holography it is silently understood that the interfering waves have the same polarization. In practice however this condition is fulfilled to a greater or lesser degree. Unequal polarization of the interfering waves results in a bias intensity which reduces the contrast of the fringes and in the limit of opposite polarization we get no fringes at all. In analysing finer diffraction effects the vector property of the light must be taken into account for example in the reconstruction of a hologram Gasvik 1976 . Special techniques have been used to reconstruct an arbitrary state of polarization Lohmann Kurtz Gasvik . Although it is possible to get along quite well with optical metrology without knowing anything about polarization it is in many cases very important to understand the vectorial properties of light. In this chapter we learn how to describe polarization and we develop a useful formalism based on Jones vectors and matrices. We also learn how to control and measure the state of polarization by means of polarization filters. The points in a light path where the change in polarization is most difficult to predict are at reflecting and refracting interfaces. Therefore this subject is treated in Section . Finally a specific optical measurement technique is based on the light s polarization. This technique called photoelasticity is described at the end of this chapter. POLARIZED LIGHT Consider a plane wave propagating in the --direction. The field amplitude is a vector denoted by u U eik- of length U at an
