Chapter 3
Rotatable-Polarisation Terahertz
Time-Domain Spectroscopy of
Anisotropic Media
In this chapter I will present a method of performing rotatable polarisation terahertz
time-domain spectroscopy (RP-THz-TDS), based on the mechanical rotation of an
interdigitated photoconductive emitter, which provides a convenient and powerful
probe of the behaviour of anisotropic materials at THz frequencies. Section 3.1 will
first explore the current methods of investigating anisotropic properties at THz frequencies, and of rotating the polarisation state of THz radiation, that are available
in the literature. Section 3.2 will outline the enhancements that were made to a standard terahertz time-domain spectroscopy system in order to allow the generation
of an arbitrarily rotatable linear polarisation state, and to detect the full polarisation state of the THz pulses at the sample position. The performance of the rotatable photoconductive emitter, compared to a polarisation rotation method using a
wire-grid polariser, will be explored in Sect. 3.3. Finally the RP-THz-TDS technique
described in this chapter is demonstrated experimentally in Sect. 3.4 by investigating
the anisotropic behaviour of two uniaxial materials, zinc oxide (ZnO) and lanthanum
aluminate (LaAlO 3 ), and the biaxial and absorbing material cupric oxide (CuO). Sections 3.2, 3.3 and 3.4 have been published as C. D. W. Mosley et al., Scientific Reports
7, 12337 (2017). Content reproduced with permission, licensed under a creative
commons license (CC BY 4.0), available at https://creativecommons.org/licenses/
by/4.0/.
3.1 Investigating Anisotropy at Terahertz Frequencies
In developing experimental methods for investigating the anisotropic properties of
materials at THz frequencies, there are two key challenges which must be addressed.
The first is the potential for a change in the polarisation state of the probing light
© 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_3
41
Rotatable-Polarisation Terahertz
Time-Domain Spectroscopy of
Anisotropic Media
In this chapter I will present a method of performing rotatable polarisation terahertz
time-domain spectroscopy (RP-THz-TDS), based on the mechanical rotation of an
interdigitated photoconductive emitter, which provides a convenient and powerful
probe of the behaviour of anisotropic materials at THz frequencies. Section 3.1 will
first explore the current methods of investigating anisotropic properties at THz frequencies, and of rotating the polarisation state of THz radiation, that are available
in the literature. Section 3.2 will outline the enhancements that were made to a standard terahertz time-domain spectroscopy system in order to allow the generation
of an arbitrarily rotatable linear polarisation state, and to detect the full polarisation state of the THz pulses at the sample position. The performance of the rotatable photoconductive emitter, compared to a polarisation rotation method using a
wire-grid polariser, will be explored in Sect. 3.3. Finally the RP-THz-TDS technique
described in this chapter is demonstrated experimentally in Sect. 3.4 by investigating
the anisotropic behaviour of two uniaxial materials, zinc oxide (ZnO) and lanthanum
aluminate (LaAlO 3 ), and the biaxial and absorbing material cupric oxide (CuO). Sections 3.2, 3.3 and 3.4 have been published as C. D. W. Mosley et al., Scientific Reports
7, 12337 (2017). Content reproduced with permission, licensed under a creative
commons license (CC BY 4.0), available at https://creativecommons.org/licenses/
by/4.0/.
3.1 Investigating Anisotropy at Terahertz Frequencies
In developing experimental methods for investigating the anisotropic properties of
materials at THz frequencies, there are two key challenges which must be addressed.
The first is the potential for a change in the polarisation state of the probing light
© 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_3
41