Quantitative phase microscopy

The quantitative phase imaging (QPI) system was based on a synthetic aperture microscope employing Mach-Zehnder interferometry [23], [24]. A He-Ne laser with a wavelength of 632.8 nm was used as a light source. The cells were prepared between two slide glasses and then placed on a live cell chamber for observation. For high-resolution and high-speed imaging, a high numerical aperture (NA) objective lens (100×, 1.4 NA, oil immersion) and a 2-D Galvanometer scanning mirrors were used. The 200 interferograms were acquired at 150 frames per second while varying the illumination angle from 0 to 1.4 NA, one at a time. All the images were converted into complex field maps using the Fast Fourier Transformation (FFT) method and then synthesized in an extended single aperture to enhance the spatial resolution and the image quality [22]. With this method, the phase information of samples was obtained with a spatial resolution of 276 nm and an improved signal-to-noise ratio.