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The nonlinear properties of Tris(acetylacetonato) Manganese(III) are used to manipulate the spatial frequencies at the Fourier plane using 4f-z scan. The technique is a simple self-adaptive all-optical system, which performs image processing and nonlinear optical measurements at the same time. Preferred spatial frequencies can be selected by shifting the nonlinear sample through the focus. Edge enhancement was demonstrated by filtering of low frequency with the nonlinear material at the Fourier plane.

The Z scan technique [_{o} + βI, where α_{o} is linear absorption coefficient, I is the intensity of the light and β is a nonlinear absorption coefficient. This coefficient contains interesting nonlinear optical effects such as: reverse saturation absorption (RSA), two photon absorption (TPA), and saturation absorption (SA). Both RSA and TPA have been well studied for optoelectronic and photonic devices [_{o} + n_{2}I, where n_{o} is the linear refractive index, I is the intensity of the light and n_{2} is a nonlinear refractive index coefficient. This coefficient is an effective parameter that contains many interesting nonlinear optical effects, such as laser-induced grating, soliton pulse propagation in waveguides [

Nonlinear optical properties of the materials can be used for spatial filtering and medical imaging [

Optical spatial filtering using nonlinear optical materials has become very popular for implantation in optical information processing [_{2} for contrast improvement [

This work demonstrates the use of nonlinear absorption properties of Tris(acetylacetonato) Manganese (III) solution for all-optical Fourier image processing and filtering spatial frequencies exploiting using 4-f filtering z scan technique. The theoretical back ground for this technique is given in references [

_{1}). Tris(acetylacetonato) manganese(III) [Mn(acac)3] solution of 1 g/l was prepared in acetylacetone as a sample and placed in 1 mm glass cuvette. The cuvette is placed at the Fourier plane for real-time processing of spatial frequency information contained in the object. The inverse Fourier transformation of the filtered spectrum is obtained using another 10 cm focal length lens (L_{2}). The transmitted beam from the sample divided into

two parts, one part of the transmitted beam is imaged on a screen at the back of the lens L_{2} and the other part is detected by the detector to obtain nonlinear properties of the sample. By shifting the sample through the focus, the beam intensity and/or spatial profile is recorded. These variations of the intensity during z scan can be used to block different spatial frequency bands of the Fourier spectrum of the image. The continuous band blocking filtering can be achieved by controlling the movement of the sample through the focus of the laser beam. Therefore no neutral density filters are needed.

Firstly the object was removed (see

The nonlinear refractive index arises from local variation of the refractive index with temperature. The absorption of the focused beam propagating through the sample leads to a spatial variation of temperature in the sample and, consequently spatial variation of refractive index that acts as thermal lens resulting in the phase distortion of the beam.

At the focus where the intensity is high, diffraction rings are formed due to the self-phase modulation of a continuous wave laser beam propagating through Tris(acetylacetonato) Manganese(III) in solution (

in the far field indicates the high value of nonlinear refractive index. Experiments are in progress to utilize the self-phase modulation technique for enhancing the contrast of biological imaging by employing the phase microscopy methods in a nonlinear regime.

The variation of intensities along the axis of the convex lens as the nonlinear sample passes through the focus can be used to simulate the intensities in different spatial frequency bands of the Fourier spectrum of the image. The spatial frequency distribution at the Fourier plane can be characterized into different intensity bands ? low spatial frequencies at the center with high intensities and high spatial frequencies on the edges with low intensities. Thus the open z scan characteristics for example RSA can be exploited for its filtering property, which is slowly controllable with z ?positions ( low incident intensity away from the focus and maximum intensity at the focus (z = 0)). At low beam intensity, away from the focus position, no nonlinear effect is present, all the spatial frequencies are transmitted through the sample cell, without the filtering process. As the intensity increases, low frequencies begin to attenuate and they diminish at higher intensities. Thus the reverse saturation absorption effects for a given sample make it possible to calculate the required input intensities to obtain the desired band of spatial frequencies.

The transmission characteristics of Tris(acetylacetonato) Manganese(III) solution as a function of intensities (positions) are used to manipulate the spatial frequencies at the focal plane.

image without any spatial filtering and

The technique is used to process blood samples for the imaging of red blood cells from normal individuals and sickle cell patients. The whole blood samples were obtained from Hematology laboratory Bahrain Defense Force (BDF) Hospital. A single drop of blood from each sample was placed on the microscope slide and left to dry for 24 hours. The blood samples were introduced as an object in the experimental setup. By controlling the input intensity entering the nonlinear sample at the Fourier plane where the nonlinear material (Mn(acac)_{3}) is placed, the edge enhancement of the blood samples was achieved.

In conclusion, the nonlinear characteristics of Tris(acetylacetonato) Manganese(III) was used to manipulate the spatial frequencies at the Fourier plane. The technique is a simple self-adaptive all-optical system, which performs image processing and nonlinear optical measurements at the same time. The technique is used in displaying

features of the red blood cells for normal individuals and for sickle cell patients, which opens the possibility of using the technique for sickle cell diagnosis. The technique also may be used for enhancing the visibility of film mammograms which may lead to early detection of microcalcification in breast cancer. The technique has a potential for optical implementation of image subtraction that can be utilized for medical image processing. Further experiments are in progress to investigate the use of this method for medical image processing.

This work is supported by RCSI-Medical University of Bahrain. The author would like to thank Dr. Seamus Cassidy for his help.

Deyari Henari,Fryad Z. Henari, (2016) Nonlinear Optical Spatial Filtering for Medical Image Processing. Open Journal of Applied Sciences,06,373-379. doi: 10.4236/ojapps.2016.67038