IMPROVING DIC MICROSCOPY WITH POLARIZATION MODULATION

It is demonstrated experimentally, as well as analytically, that when the polarization of the light incident upon the first Nomarski-Wollast on prism in a differential interference contrast (DIG) light microscop e is switched by 90 degrees, image highlights are changed into shadows and vice versa, Using an inexpensive ferroelectric liquid-crystal mod ulator, which is easily installed in the microscope, this switching ca n be done at 30 frames s(-1), synchronized to the camera. Subtraction of alternate digitized frames generates a stream of images in which co ntrast is doubled, compared with conventional video-enhanced DIG, whil e image defects and noise tend to cancel. Subtraction of alternate ima ges is carried out efficiently by frame buffer operations and amounts to massively parallel synchronous detection, The new method eliminates the problems inherent in obtaining a separate background image, as re quired by current video-enhanced DIC practice, without loss of resolut ion.