Phase-sensitive terahertz spectroscopy with backward-wave oscillators in reflection mode.

Area of Science:

• Terahertz spectroscopy
• Solid-state physics
• Electromagnetism

Background:

• Accurate characterization of solid materials at terahertz frequencies is crucial for understanding their electrodynamic properties.
• Traditional methods often struggle with nontransparent samples or require complex data processing like Kramers-Kronig transformations.

Purpose of the Study:

• To develop and validate a method for precise measurement of the complex reflection coefficient of solids.
• To enable model-independent determination of dielectric permittivity and magnetic permeability, especially for challenging materials.

Main Methods:

• Utilizing backward-wave oscillators for tunable, monochromatic coherent radiation in the 30 GHz–1.5 THz range.
• Employing a Michelson interferometer to measure the phase shift introduced by sample reflection.
• Measuring both amplitude (reflectivity) and phase of the complex reflection coefficient.

Main Results:

• Accurate measurements of the complex reflection coefficient (magnitude and phase) are achieved for solids.
• The method bypasses the need for Kramers-Kronig transformations to extract electrodynamic properties.
• Demonstrated applicability to nontransparent samples and magnetic materials with complex dynamic permeabilities.

Conclusions:

• The described method offers a powerful tool for characterizing a wide range of solid materials in the terahertz domain.
• It provides a straightforward, model-independent approach for determining key electromagnetic parameters.
• This technique is particularly valuable for studying advanced materials like metamaterials and colossal-magnetoresistance materials.