Fig 1.
Data of real and imaginary part of permittivity.
Data (black line) from Fig 3 of Sasaki et. al. Data at below 0.146 THz has been removed due to the poor signal-to-noise ratio. (a) Fit of real part of permittivity to Debye (solid gray line), Cole-Cole (dashed gray line), and Cole-Davidson (dashed black line) models. For clarity, the Cole-Cole and Cole-Davidson fits have been offset by 0.02 and 0.04, respectively. (b) Fit to imaginary part of permittivity using Debye, Cole-Cole, and Cole-Davidson models.
Fig 2.
Illustration of the external reference structure for simultaneous determination of sample thickness and refractive index.
(a) configuration for determining distance L14 in the absence of sample. (b) illustration of reflected pulses from back surface of beamsplitter, front surface of sample, back surface of sample, and reflecting mirror.
Table 1.
Summary of amber deposits sampled.
Fig 3.
(a) Visible image of a sample of Baltic Amber with flow lines and inclusions. (b) Terahertz transmission image (1.5–2 THz) through the same sample on a natural logarithmic scale (scale value equals ln(T)). For the Terahertz image (29 by 21mm), the pixel resolution is 0.2 mm. For each pixel, twelve waveforms are averaged. The speed of imaging is 5 mm/s. The entire image took approximately 10 min to acquire.
Fig 4.
Real refractive index as measured by time-of-flight versus sample age.
Botanical source and locality indicated by point shapes and colors, respectively. Horizontal bars denote age ranges noted in Table 1, vertical bars depict uncertainty of the refractive index measurements at ±0.003.
Table 2.
Table of amber sample locality, thickness, and real refractive index values as measured by time-of-flight.
Fig 5.
Comparative real and imaginary permittivity of amber localities.
Real and imaginary parts of the permittivity are calculated using Eqs (3)–(5). Real permittivity depicted on left axes with dashed lines; imaginary permittivity depicted on right axes with solid lines. (a) Lebanese and Spanish amber: Spectral response for Leb1_C (black lines), Leb1_D (dark gray lines), and Spa1_A (light gray lines) amber samples. (b) Cambay and Arkansas amber: Cam1-C (black) and Ark3-B (gray) dipterocarp samples. (c) Raritan and Burmese amber: NJ1_C (black lines) and BU-0618 (light gray lines) Cretaceous samples. (d) Mexican and Dominican amber: Mex1_B (black lines) and DR1_A (gray lines) amber samples. (e) Wyoming and Baltic amber: WY01_A (black lines) and BA-A (dark gray lines) amber samples. The spectral data of Sasaki et al. Baltic data [28] are shown in light gray.
Fig 6.
Evaluation of fraudulent synthetic amber relative to amber samples.
Extracted real (a) and imaginary (b) permittivity from selected clear amber samples. The previous Baltic Amber results of Sasaki et al. [28] are shown as a dashed line for comparison. The Sasaki et al. [28] data are in close agreement with the spectral response of Baltic Amber measured in the present paper.