P. Naulleau

STRETCH, TIME LENSES, AND INCOHERENT TIME IMAGING

The stretch, or time-lens, concept is developed further. Alternative formulations that lead to invariant systems are described, as well as methods for synthesizing the time equivalent of spatially and temporally incoherent systems.

Detection of moving objects embedded within scattering media by use of speckle methods.

Speckle-pattern subtraction methods are used for the detection of moving objects embedded in scattering media. Results show that the ability to detect small nonstationary objects is greatly enhanced.

Ensemble-averaged imaging through highly scattering media.

A method for imaging through highly scattering media is described that consists of forming a multiplicity of holograms and performing an extensive averaging process. This process produces an estimate of the phase distribution across the exiting surface of the medium. This information is combined with the available magnitude data to form an ensemble-averaged wave front that can be backprojected to form an image of absorbers within or behind the scattering medium.

Direct three-dimensional image transmission through single-mode fibers with monochromatic light

Direct three-dimensional image transmission through one single-mode or multimode fiber is demonstrated. Image transmission is carried out with a grating interferometer under monochromatic, spatially incoherent illumination.

IMAGING THROUGH OPTICAL FIBERS BY SPATIAL COHERENCE ENCODING METHODS

Coherence encoding methods are used to transmit full complex images down a pair of optical fibers (multimode or single mode). An implementation using acousto-optic deflectors is analyzed. Experimental results are given.

Motion-resolved imaging of moving objects embedded within scattering media by the use of time-gated speckle analysis

Spectral analysis of a time-evolving speckle pattern is used to provide motion-resolved detection of moving objects embedded within scattering media. Results show that the ability to detect small nonstationary scattering objects and to discriminate between objects moving at different rates is greatly enhanced.

Resolution-enhanced detection of moving objects embedded within scattering media using time-gated speckle methods.

The holographic first-arriving-light method in combination with the speckle differencing method is used to provide resolution-enhanced detection of moving objects embedded in scattering media. Results show that the first-arriving-light technique provides significant resolution improvements over standard speckle differencing.

Time-gated ensemble-averaged imaging through highly scattering media

A previously described ensemble-averaged imaging method [Opt. Lett. 21, 1691 (1996)] is extended by its combination with holographically implemented time-gated imaging. This combined method is shown to extend the effectiveness of the ensemble-averaged method by permitting imaging through thicker diffusers. Experimental results are presented.

Holographic first-arriving-light signal-to-noise ratio enhancement by differential holography

The signal-to-nose ratio of holographic first-arriving-light imaging is enhanced by differencing two sequential short coherence holograms with decorrelated fringe patterns. Imaging through 1.3 cm of chicken meat is demonstrated.

Ensemble-averaged Shack-Hartmann wave-front sensing for imaging through turbid media.

A technique is described for ensemble-averaging the light wave emerging from a turbid medium, enabling the recovery of optical information that is otherwise lost in a speckle pattern. The technique recovers both an amplitude and a phase function for a wave that has been corrupted by severe scattering, without the use of holography. With the phase estimated, an ensemble-averaged field is constructed that can be backprojected to form an image of the object obscured by the scattering medium. Experimental results suggest that the technique can resolve two object points whose signals are unresolved on the exit surface of a diffuser.