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4.5 Discussion
The single-pixel, pulsed THz camera described in this chapter does not rely on raster
scanning, or a source∕detector array, but uses random patterns for imaging. Based
on the theory of CS, the system is capable of recovering a 32 × 32 image of a rather
complicated object with only 300 measurements (~30%). This significant reduction
in number of measurements used for CS image reconstruction can speed up the ac-
quisition tremendously compared to traditional raster-scan systems. Moreover, the
reconstruction in Section 4.3 from only the amplitude measurements at a single fre-
quency is equivalent to imaging using a continuous-wave (cw) THz source. If we apply
this method directly to cw THz systems, we could use a more sensitive single-pixel
detector, such as a Schottky diode, and thus reduces the source power requirement
dramatically compared to imaging with existing multi-pixel detector arrays.
Unlike its optical counter-part which measures only intensity [60], the pulsed THz
camera can reconstruct complex images. In this case described in Section 4.4, acquisi-
tion of the entire THz waveform is necessary. The system thus obtains hyperspectral
and phase information at the expense of lower imaging speed due to the mechanical
movements of the delay line.
Currently, the major limitation of our setup is the slow translation of one random
pattern to another. However, it is clear that other schemes for binary spatial mod-
ulation of a THz beam, driven either optically or electrically, can operate extremely
rapidly and with no mechanical moving parts. Chapter 5 describes the proposed
modulation scheme in this thesis, which should allow the acquisition of sufficient
information for image reconstruction at a rate compatible with video imaging.