J. Eur. Opt. Society-Rapid Publ. 22, 14( 2026) 137
Fig. 6. a) Holographic reconstruction of a USAF MIL-STD 150A resolution chart measured in transmission. The smallest available group 9, element 3 with a line width of 0.78 lm is fully resolved as can be seen in the blow up. For reference, the red square indicates the size of a 2.5 lm camera pixel. Holographic reconstruction of the amplitude b) and unwrapped phase contrast c) of pancreas cells of the PANC-1 cell line. The cell morphology including the nucleus and cell organelle are resolved.
thus illuminating just a smaller area, which in turn results in a smaller field of view in the reconstruction. For this, we used a HeNe laser with a wavelength of k = 632.8nm as the light source. A CMOS camera with a Sony IMX541 sensor with dimensions of 5120 5120 pixels and a pixel pitch of 2.5 lm serves for imaging. However, the effective sensor length is constrained to L = 12.5 mm by the beam splitter. With the distance between object and camera being 16 mm and a refractive index of the beam splitter of n 1.5, the numerical aperture of the setup is NA = 0.55.
The numerical aperture corresponds to a diffraction limit of d = 0.57 lm. To find the actual resolution of the setup we recorded a digital hologram of a USAF MIL- STD 150A resolution chart. The hologram was reconstructed using the propagation algorithm shown in Figure 3, with the result shown in Figure 6a. The smallest available element of group 9 is fully resolved which indicates an optical resolution of below 0.78 lm. For reference the red square indicates the size of a 2.5 lm camerapixel.
Additionally, we demonstrate the capability to image biological samples on PANC-1 cells, a human pancreatic carcinoma cell line, with an average diameter of approximately 10 – 50 lm, which were suspended in culture medium and seeded onto a petri dish. As expected the cell morphology shown in Figures 6b, 6c is resolved, with observable cell cores and organelles.
For the measurement in reflection mode, e. g., for quality insurance in wafer testing, we used two types of setup, shown in Figures 4d, 4e. The setup in d also resembles that of a Mach – Zehnder interferometer as described for transmission mode, except for the object illumination. The setup in Figure 4e is in a Michelson interferometer configuration, where the reference wave is generated by reflection at a reference mirror.
We tested the achievable resolution in reflection mode using a resolution chart as well. For a higher signal-to-noise
ratio and to achieve the highest possible resolution we measured the digital hologram via temporal phase-shifting in the setup shown in Figure 4e. WeusedaCMOScamera with a Sony IMX541 sensor with 4512 4512 pixels with a pixel pitch of 2.74 lm and a supercontinuum white light laser( NKT Photonics Fianium, SuperK VARIA) at 532 nm for a shorter coherence length and thus less coherent noise. While the diffraction limited resolution given by the numerical aperture is d 0.53 lm the smallest resolved elements of the reconstructed resolution chart in Figure 7a have a line width of 0.98 lm. Consequently, we did not achieve diffraction-limited resolution in reflection. The difference in resolution can likely be attributed to distortion stemming from the lens that generates the spherical reference wave and spherical aberrations from the beam splitter cube.
To demonstrate the techniques capability in technical applications such as wafer level testing, we furthermore recorded a hologram of a micro-electronic-mechanical system( MEMS) acceleration sensor which contains object features in the low single digit micrometer range. The reference source point was generated using a tapered, lensed single mode fiber( by InZiv LTD) with a spot diameter of 0.8 lm and a working distance of 4 lm. As shown in Figure 7b the capacitors and piezoresistors with sizes of a few micrometers can be resolved across the whole field of view of 2.5 mm diameter. The MEMS sensor was measured in a single-shot measurement, using spatial phase-shifting due to the off-axis holographic setup.
For a quantitative evaluation of the resolution in both transmission and reflection mode we computed the modulation transfer function( MTF) in Figure 8 exemplarily for the reconstructions of the USAF resolution charts shown in Figures 6a and 7a respectively. For this, we evaluated the mean Michelson contrast C =( I max � I min)/( I max + I min) for the resolved resolution bar triplets. The normalized MTF of the transmission measurement stays above or