Giancarlo Pedrini

Image reconstruction for in-line holography with the Yang-Gu algorithm

A new approach to the numerical reconstruction of wave fronts stored by in-line holography is presented. The new algorithm can achieve good reconstructed results in both unitary and nonunitary systems. The influences of recording distance and noise as well as of digitalization errors on the quality of reconstruction are numerically investigated. The experimental results demonstrate the validity of this new approach.

Scatter-plate microscope: improved image acquisition

We investigate ways to improve image resolution and contrast in scatter-plate microscopy by image deconvolution and speckle pattern manipulation. Scatter-plate microscopy uses a single diffusively scattering element instead of a complex lens system to record high resolution images with almost arbitrary magnification. The image of the sample is acquired by cross-correlating the speckle pattern of a point source and the speckle pattern of the incoherently illuminated sample. The working principle is restricted by the finite range of the optical memory effect and by the quality of the light source used to approximate a point source (in our case a single mode fibre). With a deconvolution method using the autocorrelation of the point source speckle pattern as the filter function, describing the relationship between the acquired image and the original object, it is possible to compensate partially the deviation of the used point source from an ideal one. The influence of the restricted range of the memory effect can be reduced by manipulating the sample’s speckle pattern.

Ptychography: quantitative phase imaging with incoherent imaging properties

The incoherent imaging properties of ptychography are discussed in this paper. Usually a coherent light source is employed in ptychography for the recording of the diffraction patterns. However, in combination with a curved illumination it is possible to obtain an image quality of the reconstructed images that is equal to the one known from incoherent imaging. The underlying principle and results to demonstrate these findings are presented in this paper. Moreover, it will be shown that consequently not only the coherent speckle noise but likewise the resolution can be increased.

Development of a realistic wave propagation-based chromatic confocal microscopy model

A model describing the signal generation in chromatic confocal imaging is presented here. It can be used to understand the signal development process accounting for wave-optical phenomena using scalar wave theory. The influence of the optics in terms of aberrations, the specimen in terms of roughness and further parameters on the signal generation process will be investigated. Moreover, the possibility to adapt the model to investigate other spectral imaging systems, such as chromatic confocal spectral interferometry will also be shown.

Shaping the light for the investigation of depth-extended scattering media

Scattering media are an ongoing challenge for all kind of imaging technologies including coherent and incoherent principles. Inspired by new approaches of computational imaging and supported by the availability of powerful computers, spatial light modulators, light sources and detectors, a variety of new methods ranging from holography to time-of-flight imaging, phase conjugation, phase recovery using iterative algorithms and correlation techniques have been introduced and applied to different types of objects. However, considering the obvious progress in this field, several problems are still matter of investigation and their solution could open new doors for the inspection and application of scattering media as well. In particular, these open questions include the possibility of extending the 2d-approach to the inspection of depth-extended objects, the direct use of a scattering media as a simple tool for imaging of complex objects and the improvement of coherent inspection techniques for the dimensional characterization of incoherently radiating spots embedded in scattering media. In this paper we show our recent findings in coping with these challenges. First we describe how to explore depth-extended objects by means of a scattering media. Afterwards, we extend this approach by implementing a new type of microscope making use of a simple scatter plate as a kind of flat and unconventional imaging lens. Finally, we introduce our shearing interferometer in combination with structured illumination for retrieving the axial position of fluorescent light emitting spots embedded in scattering media.

Depth-resolved Hyperspectral Digital Holography

We present a depth resolved hyperspectral digital holography setup and its application for the reconstruction of amplitude and phase at different depth sections for different wavelength. For example the technique can be used for the discrimination of cells.