Self-referenced terahertz time-domain ATR spectroscopy of solutions

Abstract

Terahertz spectroscopy and imaging have emerged as sophisticated, nondestructive tools for material analysis in physical and biomedical sciences, owing to their sensitivity to molecular vibrations. However, the high absorption of terahertz radiation by water raises a significant challenge for studying liquids and biological samples. This work introduces a novel self-referenced time-domain attenuated total reflection (ATR) spectroscopy technique that overcomes this limitation by simultaneously recording both sample and reference terahertz waveforms. The method is based on ATR geometry, along with two time-delayed, synchronized sub-waveforms. This configuration enables precise differential measurements, thereby significantly improving detection sensitivity and long-term stability by mitigating environmental fluctuations and laser noise. The technique makes possible the direct extraction of both amplitude and phase information from the ATR reflection coefficient. The potential of this approach is demonstrated by measuring the relative power and phase spectra of NaCl, ATP, and saccharose solutions at various concentrations. The results obtained from this study indicate the presence of distinct spectral signatures for each molecule. This advancement opens novel prospects for high-fidelity spectral analysis, particularly in biomedical applications such as real-time monitoring of biochemical processes and cellular responses.