Source: http://aoot.osa.org/ome/abstract.cfm?uri=ome-9-4-1776
Timestamp: 2019-04-25 10:09:38+00:00

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The modulation characteristics of the polyimide-based film of SWCNTs at room temperature were studied with time-domain terahertz (THz) spectroscopy in the study. The transmission greatly reduced with an increase in the power of the external optical pump. Under the pump power of 300 mW, the transmission even decreased to 3.4% of that of the original SWCNTs sample without illumination. The modulation depth of the film reached 95.6% at 300 mW, indicating the excellent modulation effect. In addition, the optical pump greatly increased the conductivity and caused a blue shift in the real conductivity peak. In order to explore the electric field modulation characteristic of the polyimide-based SWCNTs film, the results of the conductivity at 0 mW and 300 mW under different voltages were discussed. The change in transmission at 300 mW was much more significant than that at 0 mW, indicating that the modulation effect of voltage was more obvious under the condition of illumination. However, even under the pump power of 300 mW, the modulation depth was only 41.11% at 0.7 THz. In terms of the modulation depth of the optic field and electric field, we believed that the optical modulator worked better for the polyimide-based SWCNTs film.
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Fig. 1 200 nm high interdigitated electrodes grown on silicon substrate.
Fig. 2 (a) and (b) AFM images of the sample. (c) SEM plot with a scale of 200 μm. (d) SEM image with a scale of 1 μm.
Fig. 3 The THz-TDS system schematic. A green laser is obliquely incident upon the surface of the film at 60° with regard to the polar axis.
Fig. 4 (a) Time-domain signal waveforms of the substrate and air at room temperature. (b) Time-domain signal waveforms of the polyimide -based SWCNTs film on the substrate under illumination.
Fig. 5 (a) Transmission of the polyimide -based SWCNTs film under external optical pump power from 0mW to 300mW. (b) The modulation depth of the polyimide -based SWCNTs film under external optical pump power from 0 mW to 300 mW.
Fig. 6 Measured the real and imaginary parts of conductivity of thin film at room temperature. The scatter plot was the actual measured value, and the curves were the result of simulation using the Eq. (2), which the frequency in terahertz domain were from 0.3 THz to 1 THz.
Fig. 7 (a) Plasma frequency w p under different power of the external pump. (b) Electron scattering rate γ under the action of illumination.
Fig. 8 Transmission of the polymer-based SWCNTs film under the power of external pump (0 mW and 300 mW) and different voltages.
Fig. 9 (a) Formation of space charge field in the film without illumination. E is the voltage by the interdigital electrodes. Movement of less carriers in the film with the voltage. (b) Under illumination, a lot of carriers move in the film with the voltages.
Fig. 10 (a) and (b) plasma frequency ω p of the film under the pump power of 0 mW and 300 mW and different voltages of 0 V, 10 V, 20 V, 30 V, and 40 V. (c) and (d) electron scattering rate γ of the film under the pump power of 0 mW and 300 mW and different voltages.

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