Abstract-Giant terahertz polarization rotation in ultrathin films of aligned carbon nanotubes

 

Andrey Baydin, Natsumi Komatsu, Fuyang Tay, Saunab Ghosh, Takuma Makihara, G. Timothy Noe, and Junichiro Kono

Experimental setup for showing giant THz polarization rotation in an aligned CNT film. (a) Schematic of THz transmission and reflection through the CNT film and substrate; (b) THz waveform in the time domain indicating the existence of a second pulse due to reflections in the substrate as shown in (a); (c) experimental configuration showing wire-grid polarizer, the sample, and the schematic of the polarization rotation of the propagating THz pulse; (d) polarization angle 𝜃$\theta$ defined as the angle between the CNT alignment direction and the polarization of the incident THz electric field.

https://www.osapublishing.org/optica/fulltext.cfm?uri=optica-8-5-760&id=451230

For easy manipulation of polarization states of light for applications in communications, imaging, and information processing, an efficient mechanism is desired for rotating light polarization with a minimum interaction length. Here, we report giant polarization rotations for terahertz (THz) electromagnetic waves in ultrathin (∼45nm$\sim 45\mathrm{n}\mathrm{m}$), high-density films of aligned carbon nanotubes. We observed polarization rotations of up to ∼20∘$\sim {20}^{\circ }$ and ∼110∘$\sim {110}^{\circ }$ for transmitted and reflected THz pulses, respectively. The amount of polarization rotation was a sensitive function of the angle between the incident THz polarization and the nanotube alignment direction, exhibiting a “magic” angle at which the total rotation through transmission and reflection becomes exactly 90°. Our model quantitatively explains these giant rotations as a result of extremely anisotropic optical constants, demonstrating that aligned carbon nanotubes promise ultrathin, broadband, and tunable THz polarization devices.

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