Chapter 5
High-Field Terahertz Time-Domain
Spectroscopy of Single-Walled Carbon
Nanotubes and CuO
Section 5.1 of this chapter gives a brief overview of some techniques utilised to
generate high-field THz pulses and their applications in spectroscopy. Section 5.2
then describes the setup and operation of the high-field THz-TDS system developed
as a part of this doctoral work. Section 5.3 then explores the use of indium antimonide (InSb) as a test material for the high-field THz-TDS system, before Sects. 5.4
and 5.5 present some preliminary results on high-field THz spectroscopy of highlyconductive single-walled carbon nanotube (SWCNT) films and electromagnons in
CuO.
5.1 Terahertz Spectroscopy Using Extreme Electric Fields
When the electric field strength of the THz radiation is sufficiently large, the THz
pulse can induce nonresonant effects in materials by the ponderomotive force applied
to charges via the intense, oscillating electric field. A measure of this can be gained
using the ponderomotive potential U p , given by
U p =
e
2 E
2
4mω 2 ,
(5.1)
where e is the electronic charge, m is the mass, ω is the angular frequency of the
oscillating electric field and E is the electric field amplitude. Since U p ∝ E
2
/ω
2 , the
greatest effects are observed for large electric fields with long wavelengths, hence
THz pulses can induce very large ponderomotive effects in materials. In a driving
1 THz field of ∼300 kVcm
−1 , the energy applied to free electrons in a half-cycle of
the THz pulse can approach 1 eV, comparable to the size of the bandgap in many
semiconductor materials. Examples of nonresonant effects induced by THz pulses
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
C. D. W. Mosley et al., Enhanced Polarisation Control and Extreme
Electric Fields, Springer Theses,
https://doi.org/10.1007/978-3-030-66902-7_5
89
High-Field Terahertz Time-Domain
Spectroscopy of Single-Walled Carbon
Nanotubes and CuO
Section 5.1 of this chapter gives a brief overview of some techniques utilised to
generate high-field THz pulses and their applications in spectroscopy. Section 5.2
then describes the setup and operation of the high-field THz-TDS system developed
as a part of this doctoral work. Section 5.3 then explores the use of indium antimonide (InSb) as a test material for the high-field THz-TDS system, before Sects. 5.4
and 5.5 present some preliminary results on high-field THz spectroscopy of highlyconductive single-walled carbon nanotube (SWCNT) films and electromagnons in
CuO.
5.1 Terahertz Spectroscopy Using Extreme Electric Fields
When the electric field strength of the THz radiation is sufficiently large, the THz
pulse can induce nonresonant effects in materials by the ponderomotive force applied
to charges via the intense, oscillating electric field. A measure of this can be gained
using the ponderomotive potential U p , given by
U p =
e
2 E
2
4mω 2 ,
(5.1)
where e is the electronic charge, m is the mass, ω is the angular frequency of the
oscillating electric field and E is the electric field amplitude. Since U p ∝ E
2
/ω
2 , the
greatest effects are observed for large electric fields with long wavelengths, hence
THz pulses can induce very large ponderomotive effects in materials. In a driving
1 THz field of ∼300 kVcm
−1 , the energy applied to free electrons in a half-cycle of
the THz pulse can approach 1 eV, comparable to the size of the bandgap in many
semiconductor materials. Examples of nonresonant effects induced by THz pulses
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
C. D. W. Mosley et al., Enhanced Polarisation Control and Extreme
Electric Fields, Springer Theses,
https://doi.org/10.1007/978-3-030-66902-7_5
89