Abstract-Hyperspectral data denoising for terahertz pulse time-domain holography

Maksim Kulya, Nikolay V. Petrov, Anton Tsypkin, Karen Egiazarian, and Vladimir Katkovnik

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-13-18456

We investigated data denoising in hyperspectral terahertz pulse time-domain holography. Using the block-matching algorithms adapted for spatio-temporal and spatio-spectral volumetric data we studied and optimized parameters of these algorithms to improve phase image reconstruction quality. We propose a sequential application of the two algorithms oriented on work in temporal and spectral domains. Experimental data demonstrate the improvement in the quality of the resultant time-domain images as well as phase images and object’s relief. The simulation results are proved by comparison with the experimental ones.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz pulse time-domain holography method for phase imaging of breast tissue

Nikolay S. Balbekin, Quentin Cassar,  Olga A. Smolyanskaya, Maksim S. Kulya,  Nikolay V. Petrov,  Gaetan MacGrogan,  Jean-Paul Guillet,  Patrick Mounaix,  Valery V. Tuchin, 

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10887/108870G/Terahertz-pulse-time-domain-holography-method-for-phase-imaging-of/10.1117/12.2508711.short?SSO=1

Pulse holographic imaging along with time-domain spectroscopy scan and tomographic techniques are of great interest. Since the advantages of holography are the lack of focusing optics and high spatial resolution, and, comparing with tomography, less computation cost for numerical reconstruction, this technique is preferable for the analysis of thin histological samples. In this work we have created the experimental scheme that involves measurement of diffraction pattern of the collimated THz pulse field spatial distribution at some distance behind the object in the time-domain mode, thus allowing reconstruction of amplitude and phase distribution at the object plane by numerical backpropagation of the wavefront in the spectral domain. In our experiment, we used a breast biopsy sample containing cancer tissues, we also performed numerical simulations accounting for experimental conditions to confirm the conceptual applicability of the reconstruction method.

Abstract-Increasing the resolution of the reconstructed image in terahertz pulse time-domain holography

Nikolay S. Balbekin, Maksim S. Kulya, Andrey V. Belashov, Andrei Gorodetsky,  Nikolay V. Petrov,

https://www.nature.com/articles/s41598-018-36642-3

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.

Abstract-Spatio-temporal and spatiospectral metrology of terahertz broadband uniformly topologically charged vortex beams

Maksim Kulya, Varvara Semenova, Andrei Gorodetsky, Victor G. Bespalov, and Nikolay V. Petrov

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-58-5-A90

A comprehensive characterization of the diffraction properties of terahertz (THz) pulsed broadband vortex beams consisting of several electromagnetic field oscillations requires state-of-the-art techniques for studying the evolution of a wavefront as it propagates. For this purpose, we have applied the capabilities offered by THz pulse time domain holography. Accurate metrological study of pulsed single-period THz field propagation allowed us to reveal the spatio-temporal and spatiospectral couplings in broadband uniformly topologically charged vortex beams. Here, we reveal dynamics of such beam propagation in a free space as well as in the experiment with edge diffraction with 50% blocking of the beam focal waist. In this study, we compare the dynamics of freely propagating and edge-diffracted THz vortex. Despite the fact that in the amplitude representation one can observe the emergence of strong asymmetry, analysis of the spectral trajectory of the singular point at some distance from the obstacle and the visualization of phase distribution for individual spectral components testify to the conservation of transverse energy circulation. Similar to the edge diffraction of monochromatic optical vortices, it can be interpreted as self-reconstruction of vortex properties. The given term has not previously been used for the case of pulsed broadband THz beams, to the best of our knowledge.

© 2018 Optical Society of America

Abstract-On terahertz pulsed broadband Gauss-Bessel beam free-space propagation

Maksim S. Kulya, Varvara A. Semenova, Victor G. Bespalov, Nikolay V. Petrov,

https://www.nature.com/articles/s41598-018-19830-z

Terahertz pulse time-domain holography is the ultimate technique allowing the evaluating a propagation of pulse broadband terahertz wavefronts and analyze their spatial, temporal and spectral evolution. We have numerically analyzed pulsed broadband terahertz Gauss-Bessel beam’s both spatio-temporal and spatio-spectral evolution in the non-paraxial approach. We have characterized two-dimensional spatio-temporal beam behavior and demonstrated all stages of pulse reshaping during the propagation, including X-shape pulse forming. The reshaping is also illustrated by the energy transfer dynamics, where the pulse energy flows from leading edge to trailing edge. This behavior illustrates strong spatio-temporal coupling effect when spatio-temporal distribution of Bessel beam’s wavefront depends on propagation distance. The spatio-temporal and spatio-spectral profiles for different spectral components clearly illustrate the model where the Bessel beam’s wavefront at the exit from the axicon can be divided into radial segments for which the wave vectors intersect. Phase velocity via propagation distance is estimated and compared with existing experimantal results. Results of the phase velocity calculation depend strongly on distance increment value, thus demonstrating superluminal or subluminal behavior.