Visualizing nanometric structures with sub-millimeter waves

Area of Science:

• Optics and Photonics
• Terahertz Spectroscopy
• Metrology

Background:

• Far-field imaging typically has resolution limited by wavelength.
• Near-field techniques offer higher resolution but have limited dynamic range.
• Coherent interference phenomena can enhance imaging resolution.

Purpose of the Study:

• To demonstrate sub-wavelength resolution in far-field imaging.
• To achieve high-precision height profile measurements using terahertz waves.
• To overcome the dynamic range limitations of near-field techniques.

Main Methods:

• Utilizing Fabry-Pérot oscillations within surface-structured samples.
• Employing wavelengths between 0.375 mm and 0.5 mm (0.6-0.8 THz).
• Applying a Hilbert-transform approach for optical thickness extraction.

Main Results:

• Achieved height profile precision as low as 31 nm.
• Visualized structures with heights of 49 nm (1:7500 to 1:10000 vacuum wavelengths).
• Determined thicknesses in the centimeter range, demonstrating a large dynamic range.

Conclusions:

• Far-field imaging can achieve precision comparable to near-field techniques.
• The method offers a significantly larger dynamic range than near-field systems.
• Wavelength stabilization is not required for accurate optical thickness extraction.