Many biological objects are mainly transparent and weakly scattering, thus a promising (and already widely used) way
of imaging them consists in considering optical refractive index variations. The method proposed here permits 3D
imaging of the refractive index distribution with a tomographic approach. Usually, the classical Radon transform does
not sufficiently take into account the physical interaction between light and biological cells, therefore diffraction has to
Diffraction tomography is a method that permits 3D reconstruction of the refractive index, using many captures of the
complex optical field, for example at various angles. Then, the 3D Fourier space can be filled with spatial frequencies
coming from the different views. Our setup consists in rotating the object under fix illumination and detection. The
complex scattered field needed for tomographic reconstruction is obtained from digital holographic microscopy, using
one hologram per angle of view. The method is first validated with a spherical object. Mie scattering theory is used to
simulate the measured field from which the tomographic reconstruction is performed. Experimental results on
microbeads are also presented. The wide capability of 3D imaging using diffraction tomography in biology is shown.
The limited depth-of-field is a main drawback of microscopy that prevents from observing, for example, thick
semi-transparent objects with all their features in focus. Several algorithms have been developed during the past
years to fuse images having various planes of focus and thus obtain a completely focused image with virtually
extended depth-of-field. We present a comparison of several of these methods in the particular field of digital
holographic microscopy, taking advantage of some of the main properties of holography.
We especially study the extended depth-of-field for phase images reconstructed from the hologram of a
biological specimen. A criterion of spatial measurement on the object is considered, completed with a visual
criterion. The step of distance taken into account to build the stack of images is less than the instrument
Then, preserving the distance of focus associated with each pixel of the image, a three-dimensional representation
is presented after automatic detection of the object. The limits of such a method of extraction of 3D
information are discussed.