Hidden-information extraction from layered structures through terahertz imaging down to ultralow SNR

Area of Science:

• Physics
• Spectroscopy
• Materials Science

Background:

• Noninvasive inspection of layered materials presents significant challenges for traditional time-resolved imaging.
• Signal attenuation, interlayer reflections, and dispersion degrade resolution and contrast in conventional methods.

Purpose of the Study:

• To develop a novel method for high-resolution, high-contrast noninvasive imaging of layered structures.
• To overcome the limitations of existing time-resolved techniques in analyzing complex layered materials.

Main Methods:

• Utilized terahertz (THz) time-domain spectroscopy for its broadband spectrum and fine resolution capabilities.
• Exploited local symmetrical characteristics of reflected THz pulses to identify layer locations.
• Applied spatiotemporal statistical processing to enhance image contrast, even at ultralow signal-to-noise ratios.

Main Results:

• Successfully extracted alphabetic characters from 26-layer subwavelength papers.
• Enabled accurate layer reconstruction and debonding inspection for the conservation of Terra-Cotta Warriors.
• Demonstrated high-contrast imaging and accurate structure reconstruction in layered materials.

Conclusions:

• The developed THz time-domain spectroscopy method effectively overcomes limitations in noninvasive inspection of layered structures.
• This technique offers significant potential for detailed internal inspection of diverse materials, including cultural artifacts, electronics, coatings, and composites.