Igor E. Kuchik

New algorithm for detection of dangerous objects hidden on a human body using passive THz camera

We discuss a correlation function using for developing of new algorithm that allows us to detect a hidden object without analyzing of image captured by the passive THz camera. Main idea of this approach concludes in correlation calculating between the image characteristics and corresponding characteristics of standard image. Obviously, a difference in temperature between a person body and object hidden under clothes takes place always. However, this difference can be invisible for human eyes. Using the correlation function we can increase a contrast between two objects and this allows to see an object or to produce alarm by computer. We discuss a choice of standard image characteristics for an achievement of correlation function for high contrast. Other feature of our approach arises from a possibility of a person image coming to the THz camera by using a computer processing of the image only. It means that we can “decrease” a distance between a person and the passive THz camera. This algorithm is very convenient for using and has a high performance.

Multi-modes of four-waves mixing at non-collinear interaction of laser beams in medium with cubic nonlinear response

We develop an explicit solution of problem describing collinear four-waves mixing in medium with cubic nonlinear response. This solution is carried out for set of Schrödinger equations using plane wave approximation for the case of phase matching for interacting waves. This solution allows to do full analysis of four-wave interaction modes in dependence of the problem parameters. We have shown, in particular, an existence of bistable mode for energy conversion from pump waves to signal wave under certain conditions. In general case, there are greater than 10 various modes of four-wave interaction. Knowledge about these modes is very important for spectroscopic experiment results understanding using four-waves mixing because its result depends on them in strong way. Analytical solutions and derived modes can explain complicated regime of four-wave interaction which may be appeared at high intensity of interacting waves.

Temperature resolution enhancing of commercially available THz passive cameras due to computer processing of images

As it is well-known, application of the passive THz camera for the security problems is very promising way. It allows seeing concealed object without contact with a person and this camera is non-dangerous for a person. Efficiency of using the passive THz camera depends on its temperature resolution. This characteristic specifies possibilities of the detection of concealed object: minimal size of the object, maximal distance of the detection, image detail. One of probable ways for a quality image enhancing consists in computer processing of image. Using computer processing of the THz image of objects concealed on the human body, one may improve it many times. Consequently, the instrumental resolution of such device may be increased without any additional engineering efforts. We demonstrate new possibilities for seeing the clothes details, which raw images, produced by the THz cameras, do not allow to see. We achieve good quality of the image due to applying various spatial filters with the aim to demonstrate independence of processed images on math operations. This result demonstrates a feasibility of objects seeing. We consider images produced by THz passive cameras manufactured by Microsemi Corp., and ThruVision Corp., and Capital Normal University (Beijing, China).

Expanded opportunities of THz passive camera for the detection of concealed objects

Among the security problems, the detection of object implanted into either the human body or animal body is the urgent problem. At the present time the main tool for the detection of such object is X-raying only. However, X-ray is the ionized radiation and therefore can not be used often. Other way for the problem solving is passive THz imaging using. In our opinion, using of the passive THz camera may help to detect the object implanted into the human body under certain conditions. The physical reason of such possibility arises from temperature trace on the human skin as a result of the difference in temperature between object and parts of human body. Modern passive THz cameras have not enough resolution in temperature to see this difference. That is why, we use computer processing to enhance the passive THz camera resolution for this application. After computer processing of images captured by passive THz camera TS4, developed by ThruVision Systems Ltd., we may see the pronounced temperature trace on the human body skin from the water, which is drunk by person, or other food eaten by person. Nevertheless, there are many difficulties on the way of full soution of this problem. We illustrate also an improvement of quality of the image captured by comercially available passive THz cameras using computer processing. In some cases, one can fully supress a noise on the image without loss of its quality. Using computer processing of the THz image of objects concealed on the human body, one may improve it many times. Consequently, the instrumental resolution of such device may be increased without any additional engineering efforts.

Explicit solution of FWM problem under the interaction of co-propagating laser beams in medium with cubic nonlinear response

We develop an explicit solution of the problem describing collinear four-waves mixing in medium with cubic nonlinear response. This solution is carried out for a set of Schrödinger equations using plane wave approximation under phase matching of interacting waves. This solution allows to provide full analysis of four-wave interaction modes in dependence of the problem parameters. We have shown, in particular, an existence of bistable mode for energy conversion from pump waves to signal wave under certain conditions. In general case, there are greater than 10 various modes of four-wave interaction. Knowledge about these modes is very important for spectroscopic experiment results understanding using four-waves mixing because its result depends on them in a strong way. Analytical solution and developed modes can explain complicated regime of four-wave interaction which may appear at high intensity of interacting waves.

Resolution enhancing of commercially available passive THz cameras due to computer processing

We demonstrate new opportunities for the detection of concealed objects and of clothes components due to using of computer processing of images captured by passive THz cameras, manufactured by various companies. Computer processing of images results in a temperature resolution enhancing of cameras. We achieve good quality of the image due to applying various spatial filters to show independence of processed images on math operations. This result demonstrates a validity of observable objects. We discuss also a possibility of temperature trace observing on human skin if there is a difference in temperature inside the body. We consider images produced by THz passive cameras manufactured by Microsemi Corp., and ThruVision Corp., and Capital Normal University (Beijing, China).

Possibility of passive THz camera using for a temperature difference observing of objects placed inside the human body

As it is well-known, application of the passive THz camera for the security problems is very promising way. It allows seeing concealed object without contact with a person and this camera is non-dangerous for a person. We demonstrate new possibility of the passive THz camera using for a temperature difference observing on the human skin if this difference is caused by different temperatures inside the body. We discuss some physical experiments, in which a person drinks hot, and warm, and cold water and he eats. After computer processing of images captured by passive THz camera TS4 we may see the pronounced temperature trace on skin of the human body. For proof of validity of our statement we make the similar physical experiment using the IR camera. Our investigation allows to increase field of the passive THz camera using for the detection of objects concealed in the human body because the difference in temperature between object and parts of human body will be reflected on the human skin. However, modern passive THz cameras have not enough resolution in a temperature to see this difference. That is why, we use computer processing to enhance the camera resolution for this application. We consider images produced by THz passive cameras manufactured by Microsemi Corp., and ThruVision Corp.

Computer processing of image captured by the passive THz imaging device as an effective tool for its de-noising

As it is well-known, passive THz imaging devices have big potential for solution of the security problem. Nevertheless, one of the main problems, which take place on the way of using these devices, consists in the low image quality of developed passive THz camera. To change this situation, it is necessary to improve the engineering characteristics (resolution, sensitivity and so on) of the THz camera or to use computer processing of the image. In our opinion, the last issue is more preferable because it is more inexpensive. Below we illustrate possibility of suppression of the noise of the image captured by three THz passive camera developed in CNU (Beijing. China). After applying the computer processing of the image, its quality enhances many times. Achieved quality in many cases becomes enough for the detection of the object hidden under opaque clothes. We stress that the performance of developed computer code is enough high and does not restrict the performance of passive THz imaging device. The obtained results demonstrate the high efficiency of our approach for the detection of hidden objects and they are a very promising solution for the security problem. Nevertheless, developing the new spatial filter for treatment of the THz image remains a modern problem at present time.

Co-propagating FWM of axial symmetric laser pulse with femtosecond duration

Four-waves mixing (FWM) of co-propagating femtosecond laser pulses is widely used in various practical applications for diagnostic of a medium, for example. Using the problem invariants (conservation laws for four wave pulses interaction) it is possible to develop an analytical solution of the problem under consideration in the frame-work of plane wave approximation and long pulse duration approximation (point–wise model). This solution demonstrates an existence of various FWM modes under their co-propagation. Among them, there is a mode of wave propagation without unchanging intensities. In the case of pulse propagation with inhomogeneous beam profile, this mode results in occurrence of (or oscillating) spatial-temporal domain of unchangeable intensity during certain propagation distance, which depends on SOD (second order dispersion) and beam diffraction. Both these factors destroy this propagation mode. Nevertheless, a pulse with hyperbolic cosine shape may exhibit such propertty. We investigate an influence of a pulse shape as well as a beam profile.

Analytical consideration and computer simulation of DFWM

Degenerate four-wave mixing (DFWM) for co-propagating femtosecond laser pulses is considered in the axial-symmetric case for bulk medium with cubic nonlinear response, if pump-wave amplitudes are being equal. Computer simulation is based on the set of nonlinear Schrodinger equations describing this process. For the analytical consideration we use the frame-work of both plane wave approximation and long pulse duration approximation taking into account the phase matching. In opposite to widely used approach, based on the pump-waves non-depletion, the problem invariants are used for analytical solution developing. The solution demonstrates various DFWM modes existence and allows us to provide full analysis of the problem in dependence of its parameters. Analytical solution and derived pulse interaction modes can explain complicated regime of DFWM, which may appear at different intensities of interacting waves.