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An investigation of the method of wavefront reconstruction using intensity distribution at the terahertz frequency range


N.V. Petrov, M.S. Gavrin, D.S. Andrashitov

Unambiguous definition of the task of the phase characteristics of the electromagnetic field intensity distribution is known as the inverse problem of diffraction. It belongs to a class of ill-posed problems. The most effective and simple approach to solving this problem is to use iterative methods, which are modifications of the algorithm to reduce the error. On issues such as the stagnation of the algorithm to noise and instability inherent in this method can get rid of by variation of different parameters during the measurement. This allows for the collection of real field amplitudes (hereinafter – the samples), the use of an iterative procedure which makes it possible to recover, lost in the registration of the intensity distribution of the phase information. Along with this, various phase analyzer (optical elements responsible for the phase change), and in the iterative algorithm uses various mathematical models that describe the propagation of the wave front through the setup. Variety of optical systems makes effective methods of recovery phase for the various tasks: determining aberrations, registration and correction of wave fronts, deformation analysis. Of particular interest is the adaptation of technology to reconstruct the wave front of the optic to the terahertz frequency range, due to the peculiarities of terahertz radiation: high penetrating power to the insulators, and the absence of ionizing action. Study of this issue is devoted to this work. This paper presents a method of reconstructing of the spatial distribution of the wavefront from intensity distributions. The aspects of using that method in the terahertz frequency range were analyzed. A comparison of three techniques of calculating of the propagation of terahertz field: using the Rayleigh-Sommerfeld equation, 2D Fresnel transform, and the method of distribution of the angular spectrum of plane waves was performed. It is found that the best method for using at the iterative algorithm is the distribution of the angular spectrum of plane waves.

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