Contribution of physical and system parameters in the determination of optical constants of thin solid phase samples using THz time domain transmission spectroscopy

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2024-01, Vol.304, p.123322, Article 123322
• Main Authors: Singh, Khushboo, Gupta, Shreya, Bandyopadhyay, Aparajita, Sengupta, Amartya
• Format: Article
• Language: English
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2023.123322

[Display omitted] •Estimation of refractive index of thin samples are challenging in THz spectroscopy.•Using differential data through thin pellets accurate thickness mapping has been done.•Primary causes of error - Short interaction length, porosity & non-uniform thickness.•Material specific critical thickness exists for accurate values of optical constants. Accurate estimation of complex refractive index of optically thin sample is an important challenge in terahertz time domain spectroscopy (THz-TDS). While majority of the previous studies on this topic consider Fabry-Perot (FP) effect as the primary cause of erroneous optical parameter extraction, advanced application criteria in industrial domains, such as, quality control of pharmaceutical composites or semiconductor heterostructure characterization etc. demand further assessment beyond FP effect only. Instead of conventional time-of-flight calculation pivoted to the reference data (usually obtained separately without any sample through air), we employed the differential data obtained from primary and secondary THz pulse through thin pellets to obtain accurate thickness mapping of the same. We observed that for pelletized samples with significantly larger porosity (>15%), the competing optical process like multiple internal scattering has greater impact on the accuracy of estimated optical properties. While in thin pelletized samples with smaller porosity (