Synthetic Aperture Lensless Digital Holographic Microscopy (SALDHM) for Superresolved Biological Imaging - Biomedical Optical Phase Microscopy and Nanoscopy - page 174

Figure 9.2
Recovered bandpass images of the proposed SALDHM incoming from on-axis (central image) and
off-axis (four outer images) illuminations.

beam illumination is performed and after applying the numerical reconstruction procedure
(outer images), and the conventional low-resolution image incoming from the use of on-axis
illumination (inner image). According to the experimental setup, the NA values for the
V and H directions are: NA VER 5 0.21 and NA HOR 5 0.28. These NA values define
resolution limits given by R VER 5 1.93 m. As seen in the central

image in Figure 9.2 , the last resolved elements in the test target for the V and H directions
are Group 9-Element 1 (named as G9-E1 from now on) and G9-E3, respectively,
corresponding with test target's periods of 1.95

μ m and R HOR 5 1.45 μ

m (645 lp/mm),
respectively. Those experimental values perfectly agree with the theoretical ones.

μ m (512 lp/mm) and 1.55 μ

Then, the four off-axis bandpass images are joined together with the on-axis one to
synthesize a superresolved image. In other words, an SA is generated by coherent addition
of the five individual rectangular apertures. Figure 9.3A and B depicts the conventional
rectangular aperture when using on-axis illumination and the generated SA, respectively.