High-Precision Continuous-Wave Terahertz Spectroscopy Based on a Photomixing Technique for Identifying Pearls

Area of Science:

• Spectroscopy
• Materials Science
• Gemology

Background:

• Distinguishing between natural cultured pearls and imitation pearls is crucial in gemology and commerce.
• Traditional methods may be destructive or lack definitive accuracy.
• Terahertz (THz) spectroscopy offers a non-invasive approach for material characterization.

Purpose of the Study:

• To develop and validate a continuous-wave terahertz (CW-THz) spectroscopy method for differentiating cultured pearls from imitation pearls.
• To investigate the unique spectral signatures of cultured pearls in the terahertz frequency range.
• To assess the potential of CW-THz spectroscopy for fast, non-destructive pearl identification.

Main Methods:

• Utilized continuous-wave terahertz (CW-THz) spectroscopy to obtain terahertz absorption spectra of both cultured and imitation pearls up to 0.3 THz.
• Employed Fourier transform infrared (FT-IR) spectroscopy and optical coherence tomography (OCT) for complementary analysis and validation.
• Analyzed spectral data to identify distinct absorption peaks and boundary characteristics.

Main Results:

• CW-THz spectroscopy revealed distinct terahertz absorption peaks at specific frequencies for cultured pearls, absent in imitation pearls.
• The presence of these peaks in cultured pearls is attributed to the unique nacre polymorph structure.
• FT-IR and OCT measurements corroborated the spectral findings, showing discriminative boundaries for cultured pearls.

Conclusions:

• CW-THz spectroscopy provides an accurate and non-destructive method for distinguishing cultured pearls from imitation pearls.
• The unique terahertz spectral fingerprint of cultured pearls, linked to their nacre structure, enables reliable identification.
• The proposed CW-THz system is highly suitable for rapid, non-invasive spectral analysis and authentication of pearls.