In this paper, we present a novel numerical approach for increasing the resolution of retrieved images of objects after their diffraction patterns are recorded via terahertz pulse time-domain holography (THz PTDH). THz PTDH allows for spectrally resolved imaging with high spatial resolution and does not require the fine alignment of complex optics in the THz path. The proposed data post-processing method opens up the possibility to reconstruct holograms recorded with spatially restricted THz detectors, and overcome the diffraction limit even for the lower-frequency spectral components. The method involves an iterative procedure of backward-forward wavefront propagation to simulate the field distribution beyond the initially recorded hologram area. We show significant improvement in both the object reconstruction and contrast across the whole spectrum, with qualitative resolution enhancement at lower frequency spectral components.

We present measurements of optical characteristics of sodium polyacrylate in the terahertz frequency range and discuss how material dispersion affects object visualisation in terahertz imaging. We demonstrate how important is to take into account the material dispersion for phase and relief reconstruction of the investigated object.

In this paper we consider using the terahertz (THz) time domain spectroscopy (TDS) for non destructive testing and determining the chemical composition of the vanes and rotor-blade spars. A versatile terahertz spectrometer for reflection and transmission has been used for experiments. We consider the features of measured terahertz signal in temporal and spectral domains during propagation through and reflecting from various defects in investigated objects, such as voids and foliation. We discuss requirements are applicable to the setup and are necessary to produce an image of these defects, such as signal-to-noise ratio and a method for registration THz radiation. Obtained results indicated the prospects of the THz TDS method for the inspection of defects and determination of the particularities of chemical composition of aircraft parts.

The spectra of the degraded DNA of herring are studied using two methods of THz spectroscopy that employ a femtosecond laser and a frequency synthesizer based on a BWO and a high-Q cavity. An...

In this paper, we discuss the features of numerical simulation of propagation of the two-dimensional pulsed broadband terahertz (THz) fields. A set of separate spectral components used to describe diffraction of broadband THz pulses. To eliminate sampling theorem restriction in the numerical simulation of diffraction process for the complete spectral range, we use the representation of two-dimension fields as angular spectrum for the high-frequency spectral components and the convolution of initial fields with the impulse response for the low-frequency components. The peculiarities of diffraction of pulsed broadband terahertz radiation are manifested in the form of the dips in its spectrum, which is obtained at different points of the screen. The application of the given model for THz pulsed time-domain holography is demonstrated by the reconstruction of the image of the letter “K”