Development of Polarization-Insensitive THz-to-IR Converters for Low-IR-Signature Target Detection and Imaging

Area of Science:

• Optics and Photonics
• Metamaterials
• Infrared Technology

Background:

• Terahertz-to-infrared (THz-to-IR) converters offer a pathway for detecting low-IR-signature targets.
• Metallic metasurfaces (MS) with split-ring resonator (SRR) unit cells have been explored for THz-to-IR conversion, but exhibit linear polarization dependence.

Purpose of the Study:

• To design and simulate a new dual-polarized metallic MS absorber structure that overcomes the polarization dependency of previous designs.
• To develop a model for calculating temperature difference and response time, considering all loss mechanisms.
• To compare the performance of the new cross-shaped structure with the SRR structure under coherent and incoherent illumination.

Main Methods:

• Simulation-based design of a cross-shaped unit cell metallic MS absorber.
• Development of a theoretical model to assess temperature difference and response time.
• Comparative analysis of the cross-shaped and SRR structures under varying illumination conditions (coherent/incoherent, polarized/unpolarized).

Main Results:

• The new cross-shaped MS absorber demonstrates dual-polarization sensitivity, enabling incoherent THz detection.
• Under incoherent illumination, the cross-shaped structure exhibits twice the IR emittance efficiency (temperature difference) compared to the SRR structure.
• Both structures achieve temperature differences exceeding the minimum resolvable temperature difference of state-of-the-art IR cameras.

Conclusions:

• Dual-polarized or multi-polarization-sensitive MS absorbers are critical for developing cost-effective THz-to-IR converters.
• These advanced absorbers can be effectively implemented in THz imaging solutions.
• The developed model provides a comprehensive understanding of MS absorber efficiency by including all loss mechanisms.