Fig. 1.

The principle of QWLSI, showing how a reference wavefront is applied to generate the final OPD of the cells. (1) The interferograms of the sample and reference undergo Fourier Transform (FT). (2) A pair of first-order harmonics in the Fourier space, $\stackrel{\sim }{H_x}$ and $\stackrel{\sim }{H_y}$ of the sample image, or $\stackrel{\sim }{H_{Rx}}$ and $\stackrel{\sim }{H_{Ry}}$ of the reference image, are selected and undergo inverse Fourier transform (FT⁻¹). The argument of the resultant image is the OPD gradient. Subtracting the reference OPD gradient from the sample gradient of the same direction removes the reference phase shift. (3) The 2D integration of the resultant OPD gradients produces the final OPD image.