Extreme Polarization Anisotropy in Resonant Third‐Harmonic Generation from Aligned Carbon Nanotube Films

Abstract

Carbon nanotubes (CNTs) possess extremely anisotropic electronic, thermal, and optical properties owing to their one‐dimensional character. While their linear optical properties have been extensively studied, nonlinear optical processes, such as harmonic generation for frequency conversion, remain largely unexplored in CNTs, particularly in macroscopic CNT assemblies. In this work, w e synthesized macroscopic films of aligned and type‐separated (semiconducting and metallic) CNTs and studied polarization‐dependent third‐harmonic generation (THG) from the films with fundamental wavelengths ranging from 1.5 to 2.5 μm. Both films exhibited strongly wavelength‐dependent, intense THG signals, enhanced through exciton resonances, and w e found third‐order nonlinear optical susceptibilities of 2.50 × 10−19 m2/V2 (semiconducting CNTs) and 1.23 × 10−19 m2/V2 (metallic CNTs), respectively, for 1.8 μm excitation. Further, through systematic polarization‐dependent THG measurements, w e determined the values of all elements of the susceptibility tensor, verifying the macroscopically one‐dimensional nature of the films. Finally, w e performed polarized THG imaging to demonstrate the nonlinear anisotropy in the large‐size CNT film with good alignment. These findings promise applications of aligned CNT films in mid‐infrared frequency conversion, nonlinear optical switching, polarized pulsed lasers, polarized long‐wave detection, and high‐performance anisotropic nonlinear photonic devices.This article is protected by copyright. All rights reserved

Confinement-induced nonlocality and casimir force in transdimensional systems

“…Material systems like that are currently in the process of intensive experimental development, [39][40][41] with a great potential to become the next generation advanced flexible platform for multifunctional metasurfaces and nonlinear optical devices with adjustable characteristics on demand. [42][43][44][45][46][47][48][49] Collective EM response of a TD material slab made of periodically aligned SWCN arrays was recently studied theoretically. 17,20 Being contributed by both plasmons and excitons (corresponding to intra-and interband transitions in the infrared and optical spectral regions, respectively), it was shown to be strongly anisotropically nonlocal due to the cylindrical spatial anisotropy, periodic in-plane transverse inhomogeneity, and vertical quantum confinement of the system.…”

“…Material systems like that are currently in the process of intensive experimental development, 39–41 with a great potential to become the next generation advanced flexible platform for multifunctional metasurfaces and nonlinear optical devices with adjustable characteristics on demand. 42–49…”

Extraordinary Enhancement of Nonlinear Optical Interaction in NbOBr2 Microcavities

“…Optical harmonic generation in NbOBr 2 flakes was measured using a home‐built optical setup. [ 7,8 ] The sample was excited by an optical parametric amplifier system (pulse width 150 fs, repetition rate 100 kHz). The femtosecond laser beam transmitting through a HWP was focused by an objective lens (50×, NA 0.45) to a spot of ≈2 µm in diameter.…”

“…The advent of 2D materials, such as graphene and transition metal dichalcogenides (TMDs), provides a promising platform for these nonlinear optical researches. [ 7–13 ] attributed to their unique physical properties such as the large nonlinear susceptibilities, [ 13–15 ] broadband optical response, [ 16–18 ] tunable nonlinearity, [ 19–24 ] and favorable on‐chip integration compatibility. [ 25–27 ] However, the nanoscale thickness of 2D materials imposes limitations on the light‐matter interaction length, thereby severely restricting the nonlinear conversion efficiency and harmonic generation power density.…”

Giant anisotropy and Casimir phenomena: The case of carbon nanotube metasurfaces

“…Such mate-66 rials offer new applications in quantum electron transport, 67 electron energy-loss spectroscopy, and mechanical reinforce-68 ment [20][21][22]. Ultrathin films composed of periodically 69 arranged nanotubes recently emerged as transdimensional ma-70 terials with extraordinary optoelectronic properties [23][24][25][26]. 71 Single-wall carbon nanotube (SWCN) films can also sup-72 port plasmon, exciton, and phonon-polariton eigenmodes.…”