Study of compensation of a lateral shearing Jamin-Lebedeff's interferometer

Jamin-Lebedeff's interferometer adapted for microscopy can produce a large lateral shear. It is also compensated for white light illumination working with large apertures. Unfortunately a half-wave plate assuming the compensation is not achromatic. Moreover a calcite crystal used in this interferometer is breakable. It will be shown that an association of two crystal plates whose birefringences have opposite sign offers an alternative solution. These crystal plates can't be either optically active nor too fragile and their birefringences ratio should not be too large. In addition the crystal placed in front of the objective must be more birefringent then the second one. Authors propose a combination of KDP and F2Mg crystals and have tried to achieve the best possible compensation. It is not however possible to fully compensate such a system to second order. This particular crystal association can not be either zero and second or first and second orders compensated. It has been shown that the best solution consists of a partial compensation of the second order assumed either in the direction of the shear or in the direction perpendicular to the shear. Using the crystal materials chosen as above a nearly optimized interferometer was realized without being entirely zero order compensated.