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3.2 Terahertz Time-Domain Spectroscopy (THz-TDS)
In a typical THz-TDS experiment in transmission geometry, a reference signal (E ref ,
without the sample) is collected first by scanning the Delay 1. If the sample is a freestanding solid sample, the E ref is the THz waveform of the source, detected having
nothing at the sample position. On the other hand, if the sample is a liquid or gas,
the reference signal is the THz waveform transmitted through the empty sample cell
kept at the same position at identical condition. Next, the THz waveform transmitted
through the sample (E sam ) is collected. By taking the ratio of the complex Fourier
transformation of E sam (t) and E re f (t), the complex refractive index of the sample
can be obtained as [59],
f E sam (t)
f E re f (t)
=
˜
E sam (ω)
˜
E re f (ω)
=
T (ω) exp(iϕ(ω)),
(7)
where T (ω) is the power transmittance and ϕ(ω) is the relative phase (Fig. 8).
Fig. 8 a Time-domain THz waveforms transmitted through an empty sample cell and cells filled
with alcohol samples exhibit the change in amplitude and phase. b The corresponding amplitude
spectra of the waveforms in (b). Optical parameters absorption coefficients (c) and refractive indices
(d) determined from the THz waveforms in (a) following the method described in the text. Adapted
with permission from Ref. [60]. Copyright 2017 Elsevier
S. Banerjee et al.
3.2 Terahertz Time-Domain Spectroscopy (THz-TDS)
In a typical THz-TDS experiment in transmission geometry, a reference signal (E ref ,
without the sample) is collected first by scanning the Delay 1. If the sample is a freestanding solid sample, the E ref is the THz waveform of the source, detected having
nothing at the sample position. On the other hand, if the sample is a liquid or gas,
the reference signal is the THz waveform transmitted through the empty sample cell
kept at the same position at identical condition. Next, the THz waveform transmitted
through the sample (E sam ) is collected. By taking the ratio of the complex Fourier
transformation of E sam (t) and E re f (t), the complex refractive index of the sample
can be obtained as [59],
f E sam (t)
f E re f (t)
=
˜
E sam (ω)
˜
E re f (ω)
=
T (ω) exp(iϕ(ω)),
(7)
where T (ω) is the power transmittance and ϕ(ω) is the relative phase (Fig. 8).
Fig. 8 a Time-domain THz waveforms transmitted through an empty sample cell and cells filled
with alcohol samples exhibit the change in amplitude and phase. b The corresponding amplitude
spectra of the waveforms in (b). Optical parameters absorption coefficients (c) and refractive indices
(d) determined from the THz waveforms in (a) following the method described in the text. Adapted
with permission from Ref. [60]. Copyright 2017 Elsevier