## 2 Measurement Procedure  
### Experimental Setup  
The presented DHM system in transmission mode based on the Mach-Zehnder interferometer configuration is built. As shown in Figure 1, a beam (\(\lambda=632.8\) nm) generated by a He-Ne laser source was split by a beam splitter (BS1) into two beams perpendicular to each other. One of beams was used for illuminating the sample as the object beam, the other was the reference beam for recording the information about object beam. The neutral density filter (NF1, transmittance = 10 %) between the light source and BS1 decrease the intensity of beam to prevent overexposure of CCD. The object beam,which was reflected from a mirror (M1), was expanded and collimated by a beam expander (BE1) consisting of microscope, pinhole and collimator lens. Then, the beam passed through sample was collected by the microscope (MO, NA = 0.3, 10\(\times\)). Meanwhile, the reference beam passed through a neutral density filter (NF2, transmittance = 50 %), which was able to adjust the intensity of reference beam for registering a high quality hologram, then, reflected from mirror (M2) after being expanded by a beam expander (BE2). The object and reference beam were combined by the beam splitter (BS2) with a slight angle and the image-plane hologram was recorded by CCD (Basler ace, resolution 1544 by 2064, pixels size 3.45 um). In this configuration, high precision rotation operation was required for measuring the fully topography. At the same time, the center of rotary axis needed to be placed at the optical axis for preventing transverse displacement of the tested sample in the field of view during the rotation. Therefore, a four degrees of freedom stage with manual adjustment was designed to provide four-dimensional motion with high accuracy and repeatability for the tested sample. This stage consisted of two linear axes (X, Y) with the travel range of \(\pm\)30 mm and two rotary axes (R_X, R_Y) with the rotation range of \(\pm\)90\({}^{\circ}\), as shown in the ovals of Figure 1. Two linear translators were used to move the absolute position of the intersection of the two rotary axes and assure its position coincident with the optical axis. The sample was fixed on two rotary translator which adjusts the precision tilt angle of tested sample. It was noted that the accuracy of four degree of freedom stage was so limited that every manual rotation operation carried an uncertain alignment error, so it was essential to execute the re-alignment procedure in the subsequent multi-angle stitching process. Furthermore, the microscope, whose NA decides the frequency bandwidth of the whole measurement system, was just like a low pass filter and the object wave corresponding to the large gradient region of sample carried high frequency spatial information, so we can say the NA of MO severely restrict the capability to measure the large gradient topography. In conventional DHM, if the large gradient object whose NA is larger than the NA of MO then it is vertically transmitted by a plane wave, as shown in Figure 2a, only the red part of beam which carry the topography information of small gradient region of object can be received by MO. Meanwhile, the blue part of beam was lost and cannot generate a dark area without any surface information in hologram. However, in the multi-angle stitching method, the DHM system was improved by adding four degrees of freedom stage which can provide multiple inclination angle for the sample. By means of rotation, the angle between normal direction of the large gradient region of sample and direction of incident ray was decreased and the area's surface feature can be captured by MO, as shown in Figure 2b,c and we can also measure shape surface with larger gradient while rotation angle was adjusted to be larger  
Figure 1: Schematic of the digital holography microscopy (DHM) system setup in transmission configuration with four degree of freedom stage.