148
A. Saha
Fig. 2 a Typically acquired THz traces at different positions throughout the sample. b The
electric field amplitude at t 0 = 27.6 ps: E xy (t 0 ). c Normalized amplitude of the main
peak: max
E xy (t)
/max(|E ref (t)|). d Delay between the main peak and a reference peak:
t
max
E xy (t)
− t{max[|E ref (t)|]}. Adapted with permission from [30] © The Optical Society
discussed in the previous section, the slow rate of THZ image formation is the first
problem. This happens due to the use of single-pixel THz detectors which are easily
available commercially. Hence, to produce an image, a serial point-by-point mechanical scanning of the sample is required. Alternatively, 2D THz-TDS photoconductive
antenna arrays or 2D electro-optic sampling (EOS) can be used. The second problem
is that, to obtain the temporal/spectral dimension, an optical delay line is required.
Usually, a pair of mirrors mounted on a micropositioning stage forms the optical delay
line. But it is difficult to move the delay line mechanically in real-time operation.
3.2 Terahertz Reflection, Transmission and Conductivity
Imaging
It is seen that for a terahertz waveform, both the amplitude and the phase can be
extracted in the THz-TDS measurements. The refractive index which is complex in
A. Saha
Fig. 2 a Typically acquired THz traces at different positions throughout the sample. b The
electric field amplitude at t 0 = 27.6 ps: E xy (t 0 ). c Normalized amplitude of the main
peak: max
E xy (t)
/max(|E ref (t)|). d Delay between the main peak and a reference peak:
t
max
E xy (t)
− t{max[|E ref (t)|]}. Adapted with permission from [30] © The Optical Society
discussed in the previous section, the slow rate of THZ image formation is the first
problem. This happens due to the use of single-pixel THz detectors which are easily
available commercially. Hence, to produce an image, a serial point-by-point mechanical scanning of the sample is required. Alternatively, 2D THz-TDS photoconductive
antenna arrays or 2D electro-optic sampling (EOS) can be used. The second problem
is that, to obtain the temporal/spectral dimension, an optical delay line is required.
Usually, a pair of mirrors mounted on a micropositioning stage forms the optical delay
line. But it is difficult to move the delay line mechanically in real-time operation.
3.2 Terahertz Reflection, Transmission and Conductivity
Imaging
It is seen that for a terahertz waveform, both the amplitude and the phase can be
extracted in the THz-TDS measurements. The refractive index which is complex in