Dual-wavelength diffraction phase microscopy with 170 times larger image area

Image area for multiple-color three-dimensional (3-D) off-axis interferometry is extremely restricted because of the Nyquist sampling rate, autocorrelation term, and twin cross-correlation term in the frequency domain for each wavelength. Furthermore, the image area is more restricted in dual-wavelength diffraction phase microscopy, which is an important tool for 3-D biological imaging with subnanometer sensitivity. The reason for this extra restriction is the use of only one pinhole for generating two uniform reference beams, which is not sufficient for imaging large areas. Here, we developed large field-of-view double-pinhole dual-wavelength diffraction phase microscopy as a novel approach to capture maximum possible information using two arbitrary wavelengths in the off-axis arrangement. The rules to optimize the two-dimensional sampling scheme without any crosstalk for two arbitrary wavelengths are theoretically presented. We demonstrate that the loss in the image area of the dual-wavelength holographic system designed with this approach is limited to 0-11% of the maximum possible image area using single-wavelength off-axis interferometry. Total amount of information is more than 170 times that of previously reported dual-wavelength diffraction phase microscopy employing single grating, single pinhole, and no sampling scheme optimization. Feasibility of the technique with sub-nanometer sensitivity is demonstrated by measuring optical thickness of polystyrene microspheres.