Transparent stepped phase measurement using two illuminating beams

We propose a single shot and single wavelength phase imaging technique for measuring phase of the transparent objects without using unwrapping process. A grating between a laser and the object is used to make beams with different angle, which determines the measurement range of the microscope. The grating pitch and magnification of the lens system before the sample affect the angle. The angle inside the object is changed according to Snell's law; therefore, final angle is related to the refractive index of the object. Magnification of the lens system after sample will control the modulation frequency of microscope. The interference pattern is constructed at CCD plane and convey information of the sample. For a phase below the measurement range of the microscope, the reconstructed phase is not wrapped. By increasing the measurement range accuracy of the system will drop; therefore the magnification of the lenses must choose carefully to obtain optimal phase. The ability of this technique is demonstrated by reconstructing phases of two transparent step objects with 150 and 510 μm height. Their refractive indexes for red light are 1.515 and 1.508 , respectively. Therefore, total optical path length difference is 336 micrometers that is 500 times more than the laser wavelength. The phase is successfully reconstructed without using unwrapping algorithms.