In this paper we present a three dimensional numerical model, based on a Pseudo-Spectral Time Domain algo- rithm (PSTD), that simulates the propagation of light carrying an image through a scattering medium and the back propagation of the scattered light which is re ected back by a phase conjugate mirror, modelled thanks to the nonlinear optical process of three-wave-mixing. We show how the phase conjugate wave retraces the scattering path and retrieves the spatial information of the input image with a signal to noise ratio that depends on the lateral dimensions of the phase conjugate mirror and of the number of realizations cumulated. Moreover, we show that the image restoration is not precluded by the polarization change between the phase conjugate wave and the scattered light exiting the complex medium.
We show that phase-conjugation by three-wave mixing allows turbidity suppression through biological tissues with thicknesses up to 5 mm, at a near-infrared wavelength included in the therapeutic window. Because of the ultrafast character of the imaging process, a motion of the tissue, which mimics in vivo imaging, can be exploited to significantly improve the signal-to-noise ratio and the resolution of the restored images.
In this paper we present results of real-time imaging through biological tissues by means of nonlinear three-wave mixing phase conjugation process. Biological tissues with thicknesses up to 5 mm are used and the imaging process is performed at a near infrared wavelength included in the therapeutic window. Furthermore we show that real-time compensation of turbidity of biological tissues allowed with this method can be applied to scattering media in motion, with a significant improvement of the signal to noise ratio and resolution of the restored images.
We report semi-classical numeric simulations of the quantum spatial fluctuations in parametric amplification of images limited by the shot noise. Noiseless amplification of images is demonstrated by the use of a degenerate type 2 phase sensitive amplifier.
The picosecond parametric amplification of a polychromatic image with a wavelength bandwidth of 140 nm and a gain of 15 dB has been obtained in a type I, LBO crystal. Thirty per 30 points were resolved. These results are in good agreement with a numerical study of the phase-matching conditions around the collinear degeneracy where phase-matching is non- critical for the signal beam in angle as well as in wavelength.
The linewidth measurement on wafers depends on the small local irregularities in the region being tested. Such defects must be first of all detected and then canceled in order to give an estimation of the average linewidth. Image processing based on the Karhunen-Loève transform of multiple acquisitions in different experimental conditions is proposed.
Using statistical information compression, irregularities are easily detected and efficient noise filtering is performed.
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