Nonlinear phase contrast microscope

Phase contrast microscopy, is a technique that can be used to produce high-contrast images of transparent objects. The technique employs a phase mask, at the object Fourier transform plane, to create a synthetic reference wave that interferes with the object wave at the image plane. However, the fabrication and alignment of these masks is an expensive and delicate process. In this work, we present a nonlinear phase contrast microscope that can be implemented with a conventional optical microscope using a low power CW coherent light source to illuminate the specimen. An intensity dependent refractive index material is used to photoinduce the filter. Therefore, the aligning procedure is greatly simplified. The nonlinear material is a thin cell of dye doped liquid crystal where it is possible to produce a tunable phase delay depending on the incident light intensity, the light polarization, and the temperature. Due to these characteristics the resulting setup is relatively inexpensive, easy to implement, and extremely robust.