102
5 High-Field Terahertz Time-Domain Spectroscopy …
strength is increased, the transmission of the THz pulses increases, consistent with
the previous observations in the literature [8]. An increase in transmission of around
40% is observed for the highest electric field strength of 373 kVcm
−1 . The data
at field strengths higher than 85 kVcm
−1 have been fit to a straight line in Fig. 5.7b,
with a gradient of 0.00125 cm kV
−1 . Saturation of the THz transmission has not been
observed up to electric fields of 373 kV cm
−1 , and the data at high field strengths show
no deviation from the linear increase in transmission.
The consistency of the observed behaviour with other reports in the literature
demonstrates that the high-field THz-TDS system operates as intended, and InSb
may be used as an effective test material for high-field THz systems. Future experiments may extend these measurements to higher field strengths, in order to observe
saturation behaviour in InSb.
5.4 Nonlinear THz Transmission in Single-Walled Carbon
Nanotube Films
The unique optical and electronic properties of single-walled carbon nanotubes
(SWCNTs), such as 1D ballistic conduction, large exciton binding energies and
strong many-body interactions [58, 59], has driven much recent research into their
applicablity for use in device applications [60, 61], and in THz devices [62, 63].
THz spectroscopy provides a non-contact method of probing the motion of charges
in nanomaterials [64, 65], and has previously been utilised to explore the conductivity
of SWCNT films [66].
In a SWCNT film, both the conductivity of a single nanotube and the conductive
network of intertube contacts play an important role in defining the overall macroscopic properties of the film [67–69]. The conductivity of SWCNT films at THz
frequencies can be described by a Drude-plasmon model [39, 40, 70], in which
there is a combination of a Drude-type free-carrier response, whereby charges are
transported over long intertube distances throughout the nanotube network, and a
plasmon-type resonance, describing the collective contribution of charges confined
to individual nanotubes.
As CNTs gain popularity in device applications, their properties in the high-field
regime are becoming of greater interest, and as such experimental insight is vital to
their use in future device applications. The following section will describe preliminary results into the high-field behaviour of SWCNT films, which show promise for
future investigations into their behaviour in this regime.
5 High-Field Terahertz Time-Domain Spectroscopy …
strength is increased, the transmission of the THz pulses increases, consistent with
the previous observations in the literature [8]. An increase in transmission of around
40% is observed for the highest electric field strength of 373 kVcm
−1 . The data
at field strengths higher than 85 kVcm
−1 have been fit to a straight line in Fig. 5.7b,
with a gradient of 0.00125 cm kV
−1 . Saturation of the THz transmission has not been
observed up to electric fields of 373 kV cm
−1 , and the data at high field strengths show
no deviation from the linear increase in transmission.
The consistency of the observed behaviour with other reports in the literature
demonstrates that the high-field THz-TDS system operates as intended, and InSb
may be used as an effective test material for high-field THz systems. Future experiments may extend these measurements to higher field strengths, in order to observe
saturation behaviour in InSb.
5.4 Nonlinear THz Transmission in Single-Walled Carbon
Nanotube Films
The unique optical and electronic properties of single-walled carbon nanotubes
(SWCNTs), such as 1D ballistic conduction, large exciton binding energies and
strong many-body interactions [58, 59], has driven much recent research into their
applicablity for use in device applications [60, 61], and in THz devices [62, 63].
THz spectroscopy provides a non-contact method of probing the motion of charges
in nanomaterials [64, 65], and has previously been utilised to explore the conductivity
of SWCNT films [66].
In a SWCNT film, both the conductivity of a single nanotube and the conductive
network of intertube contacts play an important role in defining the overall macroscopic properties of the film [67–69]. The conductivity of SWCNT films at THz
frequencies can be described by a Drude-plasmon model [39, 40, 70], in which
there is a combination of a Drude-type free-carrier response, whereby charges are
transported over long intertube distances throughout the nanotube network, and a
plasmon-type resonance, describing the collective contribution of charges confined
to individual nanotubes.
As CNTs gain popularity in device applications, their properties in the high-field
regime are becoming of greater interest, and as such experimental insight is vital to
their use in future device applications. The following section will describe preliminary results into the high-field behaviour of SWCNT films, which show promise for
future investigations into their behaviour in this regime.