TERAGAS Consortium – Mid-term Scientific & Secondment Review

Project Context & Administrative Notes

  • Meeting opens with gratitude for contributors; moment of silence for fallen colleagues.
  • Series of technical presentations from multiple partners within the EU "TERAGAS" consortium.
  • Focus: development of quasi-optical technologies, new anisotropic dielectric/semiconductor materials, devices for 0.1\,\text{–}\,3\;\text{THz} radiation control.

Consortium, Call & Acronym

  • Project number & acronym shown (TERAGAS) – a MSCA Staff Exchange action.
  • Beneficiaries/partners: Lviv Polytechnic National Univ., Warsaw Univ. of Technology (WUT), Univ. of Angers, Soft-Partners, Electron-Carat, ENOSA, SPC (Scientific Production Centre), etc.

Principal Goal

  • Develop innovative quasi-optical technologies enabling efficient use of dielectric, semiconductor and nanocomposite anisotropic materials as functional elements in THz control devices → target market-ready products.

Eight Research Objectives

  1. Organise a network-wide research & training programme.
  2. State-of-the-art review & material selection (dielectric, semiconductor, crystalline, nanocomposite).
  3. Develop / validate characterisation techniques in the THz spectral range.
  4. 3-D analysis of spatial anisotropy; optimisation of sample geometry.
  5. Study influence of optical-beam intensity & external \mathbf{E}-field on semiconductor properties.
  6. Fabricate & test lab prototypes of quasi-opto-electronic cells from bulk crystals.
  7. Fabricate & test prototypes based on photo-generation of carriers + complementary structures.
  8. Translate quasi-optical technologies & engineered materials into innovative products.

Work-Package (WP) Structure

  • 8 WPs; inter-dependencies illustrated via PERT & Gantt charts.
  • Each coordinator later delivers detailed WP updates.

Expected Scientific/Technological Impact

  1. Novel/improved technologies
    • Controlled crystallisation of crystalline–nanocomposite \text{Bi}4\text{Ge}3\text{O}{12} & \text{Bi}4\text{Si}3\text{O}{12}.
    • Computer-simulated lattice-dynamics for photonic crystals; THz transmission-line tests (Si, Ge, Se).
    • Software for band-structure & band-gap calculations; spatial-anisotropy solver.
    • Feasibility of millimetre-wave lens antennas.
  2. Prototypes
    • THz modulator on bulk / film / nanocomposite with highest efficiency (optically controlled).
    • Acoustically controlled THz device (surface acoustic waves + photo-generated carriers).

Individual Presentation Highlights

1. Prof. Anatoly Andrusyak (Lviv Polytechnic)

  • Reiterates objectives, WPs, expected impacts.

2. Prof. Marian Kryk – Selenium Thin Films

  • Aim: structural, electrical & optical characterisation of amorphous vs trigonal Se films made by thermal sputtering.
  • Key points:
    • Amorphous \rightarrow trigonal transition ≈ 130\,^{\circ}\text{C}.
    • Dark resistivity high; holes dominate drift conduction.
    • Under visible/IR illumination: resistance drops via carrier generation.
    • THz sensitivity linked to collective oscillations.
    • Challenges: instability of amorphous films under long-term irradiation.
    • Potential for wide-band detectors.

3. Dr. Ihor Burdon & Prof. Ivan Stus

Part A – Porous Alumina Matrices + Organic Crystals

  • Used gas-porometry, SEM/EDS; deposited adipic acid (ADPA) & KABA-5 crystals.
  • Result: homogeneous ADPA distribution; exclusive mesoporosity confirmed via N_2 adsorption–desorption isotherms.

Part B – Nanoporous Carbon–Ni Composites

  • Two-stage pyrolysis of hydrolysis lignin + nitrogen doping.
  • Observed ferromagnetism & broad pore-size distribution.

Part C – Piezoelectric Anisotropy Modelling (Prof. Stus)

  • Extreme-surface method → maximised electromechanical coupling (k_{\text{EM}}).
  • \text{LiNbO}3: predicted k{\text{EM}} ≈ 30\% higher than literature for indirect cuts.
  • \text{Li}2\text{B}4\text{O}_7: achieved top literature values.
  • Orientation & field optimisation boosts k_{\text{EM}} by tens of percent.

4. Prof. Andrii Kityk – Multi-institution Secondments

  • Six separate secondments summarised; activities included:
    • Liquid-phase epitaxy of Bi-doped iron garnet layers.
    • Z-scan & SHG setups (Univ. Angers).
    • Fabrication/characterisation of polymer–inorganic composites, twist-bend nematics (TBN) in porous matrices.
    • Modernisation of TeraScan 1550 THz spectrometer (Soft-Partners).
    • Transmission spectra of Si/Ge (bulk & porous) 0.1\text{–}1.35\,\text{THz} under illumination.
  • Key publications: ACS Nano on phase transitions in Al$2$O$3$ + LC composites; Opt. Mater. submission on Si/Ge THz photo-modulation.

5. Prof. Krystyna Wroblewska – KBT Ceramics & Composites

  • \text{K}3\text{Ba}2\text{TiO}_8 (KBT) perovskites via solid-state synthesis; sintering temp/time optimised.
  • Doping altered grain size & shape; optical absorption peaks at 532 & 1064\,\text{nm}.
  • SHG measured in reflection & transmission (sample thickness 5\rightarrow0.5\,\text{mm}).
  • Limitation: low damage threshold \Rightarrow developed epoxy/KBT & epoxy/KDP composites.
  • Polarisation of crystals inside composite planned to induce macroscopic anisotropy.

6. Prof. Yaroslav Yashchyshyn – Sub-THz Second Harmonic Generation (SHG)

  • Setup: f_{\text{in}} = 50\text{–}60\,\text{GHz}, detect 2f at 105 & 120\,\text{GHz}.
  • Components: power amp, band-stop filter (suppresses source-generated 2f), rotatable polariser & sample goniometer.
  • Samples: \text{SiC} & \text{LiNbO}_3 plates.
  • Observations:
    • Clear SHG peak (−80 dBm) above noise floor (−115 dBm).
    • Angular & polarisation dependence mapped in 3-D.
    • Quadratic power law confirmed (P{2\omega}\propto P{\omega}^2).

7. Dr. Svitlana Holovats – Bismuth Silicon/Germanium Oxides & Epoxy Nanocomposites

  • Capillary crystallisation inside nanoporous Al$2$O$3$ under \mathbf{E}-field produced oriented 200 textured Bi crystals.
  • XRD verifies crystal survival after composite curing.
  • Additional work: epoxy + KDP/TGS micro-powders; XRD shows KDP stable, TGS partly reacts with epoxy.
  • Overall objective: low-cost, thick (> mm) nonlinear THz media.

8. SPC (Dr. Volodymyr Sirenko)

  • Implemented FFT-based filtering of noisy transmission data in 85\text{–}145\,\text{GHz} band.
  • Extracted \varepsilon'(f), \varepsilon''(f), n(f), k(f) for Si, Ge, BSO, BGO.
  • Optical pumping (LED) of Ge wafers: > 80\,\text{dB} modulation depth.
  • Plan: ship optimised Ge to Prof. Yashchyshyn for SHG-style modulation tests.

9. Electron-Carat Reports (Prof. S. Kukowski)

  • Fabricated BGO plates, Lithium-Niobate optical elements, Ge wafers.
  • Developed thin-film Au contacts for cochlear-type LiNbO$_3$ structures (second-harmonic generation).
  • THz S-parameter mapping (70\,\text{–}\,120\,\text{GHz}) of LT-GaAs / semi-insulating GaAs epi layers:
    • Correlated conductivity, layer thickness, dopant type (Al, Si) to THz transmission.
  • Collaborative coordination of material lists across partners.

Cross-cutting Technical Themes

  • Thin-film deposition: thermal sputtering (Se), liquid-phase epitaxy (Bi:IG), LPE of LiNbO$_3$.
  • Porous templates: anodic Al$2$O$3$, nanoporous Si (electro-etching).
  • Nonlinear optics techniques: SHG, THG, Z-scan, corona-poled polymers.
  • Numerical tools: DFT (Gaussian), SPEDS-F elastic/optic solver, extreme-surface method, custom MATLAB for FFT filtering.
  • Spectrometers: TeraScan 1550 (0.1–1.75 THz), VSM magnetometer, Raman, SEM/EDS, gas-sorption porometry.

Equations & Quantitative Data

  • Phase-match condition: n{\text{opt}}(\omega) = n{\text{THz}}(\Omega) (critical for optical rectification).
  • Electromechanical coupling: k_{\text{EM}} = \sqrt{\dfrac{\text{stored}\;\text{mechanical}\;\text{energy}}{\text{input}\;\text{electrical}\;\text{energy}}}.
  • SHG efficiency scaling: P{2\omega} \propto (\chi^{(2)})^2 L^2 I{\omega}^2.
  • Observed THz modulation depth in Ge: >80\,\text{dB} for I_{\text{LED}} \approx 100\,\text{mW/cm}^2.

Ethical, Practical & Market Considerations

  • Target is market-ready THz modulators/filters; industry partner Soft-Partners involved in prototyping.
  • Environmental & safety aspects: handling of Se films (toxicity), nano-carbon Ni composites (inhalation risk), epoxy curing.
  • Training ESR/ER through secondments improves EU human capital in THz photonics.

Connections to Previous & Future Work

  • Builds on IMAGE, NANOCOM, and earlier FP7 projects (nano-composite optics).
  • Next steps: phase-matched optical rectification with LiNbO$_3$, organic crystals; integrate Ge-based optically-controlled shutters into quasi-optical benches; scale epoxy/KDP composites for >1\,\text{THz}.
  • Plan to exploit new Ti:Sapphire <100\,\text{fs} laser at Univ. Angers for broadband THz generation.

Key Takeaways

  • Consortium achieved multi-material platform (Si, Ge, Se, LiNbO$_3$, KBT, KDP, bismuth oxides) suitable for diverse THz control mechanisms: optical, acoustic, electrical.
  • Demonstrated sub-THz SHG and >80\,\text{dB} photo-modulation – rare within 50\text{–}120\,\text{GHz}.
  • Oriented nanocomposites and low-cost polymers emerge as scalable THz nonlinear media.
  • Numerical & experimental tool-set now in place for full dielectric-function extraction and device optimisation.