Disclosed is an imaging apparatus for IR four-wave mixing polarization microscopy. The apparatus can include pump and probe beam sources, a polarizer, a beam combiner, a scanner, an optical focusing system, a collecting optical system, a dichroic beam splitter, a polarizing beam splitter, a photodetector, a polarization differential detector, and a data analyzer. The technology can be used to obtain a molecular vibrational microscopic image using a polarization-dependent nonlinear spectroscopic signal obtained through the focusing and spatial scanning of multi-wavelength laser beams in a sample.