Sensing and Analysis of THz-Radiation using the Coherence Function (SensATion)

• Applicants: Professor Dr. Ralf Bernhard Bergmann; Professor Dr. Martin Koch
• Subject Area: Measurement Systems ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 423266368

• Final Report Year: 2023

Final Report Abstract

Terahertz (THz) radiation is a part of the electromagnetic spectrum between microwaves and infrared radiation with frequencies between 100 GHz and a few THz. It is not ionizing and has several other advantages, including the ability to penetrate many materials that are opaque to visible light and can be used to detect and identify chemicals and materials like drugs and explosives. Coherent imaging techniques in the THz range have been developed, allowing for advanced applications like quantitative phase contrast imaging, digital holography, and ultra-fast spectroscopy. However, current techniques rely on a superposed reference wave field or reference optical pulse. New methods are therefore required for characterizing unknown THz radiation from various sources ranging from antennas to stellar objects. This project closes the gap in the state of the art of researching and developing methods that provide reference-free wave field sensing in the THz range. The approach followed here is based on sampling of the mutual coherence function (i.e. the spatial coherence) using a shear interferometer. This work presents the first recording and analysis of a-priori unknown THz radiation even in the case of partial spatial coherence. Future applications of this development range from characterization of photonic components, antennas, self-luminous and distant objects as well as investigations in quantum optics. Furthermore, currently existing applications in coherent imaging largely benefit from a reference-free technique. Avoiding the need of guiding and controlling a reference wave enables novel flexible and compact coherent imaging sensors that can be used like a mobile camera.

Publications

• Quasioptical components for the THz-regime: Fabrication and characterization, in: DGaO Proceedings, 2021-P009-9 (2021)
  M. Agour, C. Falldorf, F. Taleb, E. Castro-Camus, M. Koch, R. B. Bergmann
  
• Characterization of terahertz wavefront aberrations using computational shear-interferometry. Optical Engineering, 61(11).
  Agour, Mostafa; Falldorf, Claas; Taleb, Fatima; Castro-Camus, Enrique; Koch, Martin & Bergmann, Ralf B.
  
• Chocolate inspection by means of phase-contrast imaging using multiple-plane terahertz phase retrieval. Optics Letters, 47(13), 3283.
  Agour, Mostafa; Falldorf, Claas; Taleb, Fatima; Koch, Martin; Bergmann, Ralf B. & Castro-Camus, Enrique
  
• Exploring the coherence function for optical metrology and beyond. Optics and Photonics for Advanced Dimensional Metrology II (2022, 5, 20), 11. American Geophysical Union (AGU).
  Falldorf, Claas
  
• Shear interferometry for terahertz wavefront sensing. Terahertz Photonics II (2022, 5, 31), 21. American Geophysical Union (AGU).
  Agour, Mostafa; Falldorf, Claas; Taleb, Fatima; Castro-Camus, Enrique; Koch, Martin & Bergmann, Ralf B.
  
• Terahertz referenceless wavefront sensing by means of computational shear-interferometry. Optics Express, 30(5), 7068.
  Agour, Mostafa; Fallorf, Claas; Taleb, Fatima; Castro-Camus, Enrique; Koch, Martin & Bergmann, Ralf. B.