Apparatus for High-Precision Angle-Resolved Reflection Spectroscopy in the Mid-Infrared Region

Area of Science:

• Optics and Photonics
• Materials Science
• Spectroscopy

Background:

• Fourier transform (FT) spectroscopy, particularly Fourier transform infrared (FT-IR), is crucial for analyzing material optical responses.
• Standard FT-IR setups focus light, limiting analysis of angle-dependent optical characteristics.
• Investigating angle-resolved optical properties is essential for advanced material characterization.

Purpose of the Study:

• To design and build a high-precision angle-resolved reflection setup compatible with commercial FT-IR spectrometers.
• To overcome the limitations of standard FT-IR setups in analyzing angle-dependent optical phenomena.
• To enable detailed characterization of materials with in-plane anisotropy.

Main Methods:

• Developed a novel setup that converts a focused beam into an achromatically collimated beam with high angle dispersion (0.25°).
• Integrated the setup into a commercial FT-IR spectrometer, allowing incident angle scanning over ~8°.
• Utilized an HgCdTe detector, reducing beam diameter to ~1 mm for enhanced sensitivity.

Main Results:

• Successfully measured angle-dependent mid-infrared reflectance of 2D photonic crystal slabs.
• Determined the in-plane dispersion relation near the Γ point in momentum space.
• Observed the formation of photonic Dirac cones, characterized by linear dispersions and accidental degeneracy at Γ.

Conclusions:

• The developed angle-resolved reflection setup is effective for characterizing materials with strong in-plane anisotropy.
• The apparatus facilitates the study of photonic crystal waveguides, plasmonic metasurfaces, and molecular crystalline films.
• This technique provides new insights into the optical properties of advanced nanostructured materials.