Visualizing the conoscopic isochromatic interference fringes in anisotropic crystals by spinning polarizer and analyzer.

In conventional conoscopic interference patterns of optically anisotropic materials the isochromatic interference fringes are inherently masked by the dark isogyres. We prove that the isochromatic fringes can be directly visualized by spinning the crossed linear polarizer and analyzer, regardless of the polarization state of the incident light. This simple method completely eliminates the isogyres and reveals the whole isochromatic fringes without the need of any additional optical elements or calculations. The system works at any wavelength that the linear polarizer permits. The validity of this method is demonstrated by observing the interference patterns of an LiNbO(3) electro-optic crystal under different external electric fields.