Near-field imaging of mid-infrared surface phonon polariton propagation

Abstract

We demonstrate that mid-infrared surface phonon polariton propagation on a SiC crystal can be imaged by scattering-type near-field optical microscopy. From the infrared images, we measure the wave vector and the propagation length of locally excited surface phonon polaritons. Our method can be also applied to surface plasmon polaritons and allows to study surface polaritons in subwavelength-scale structures.

One-dimensional surface phonon polaritons in boron nitride nanotubes

“…1d and Methods). s-SNOM has been previously used to study phonons 25 and SPhPs in planar materials 19,26,27 . In this technique, a sharp metallic probe produces an optical near-field with high spatial frequencies that enables sub-diffraction limit imaging with 10 nm spatial resolution.…”

Second harmonic generation spectroscopy in the Reststrahl band of SiC using an infrared free-electron laser

“…We observe two distinct spectral features in the SHG response, one at the TO frequency resulting from the resonance in the nonlinear susceptibility χ (2) , and another one in the LO frequency range due to resonant enhancement of the Fresnel transmission. Theoretical modeling of the SHG spectra reveals the details of the underlying mechanisms, showing that mid-IR SHG is very sensitive to the critical features of the linear and nonlinear optical response in the Reststrahl band.…”

“…For χ (2) , Flytzanis 23 considered three different contributions containing linear, 2nd, and 3rd order terms of TO phonon resonances, which are usually denoted Faust-Henry, 24 electrical and mechanical anharmonicity, 23,25 respectively. In consequence, the χ (2) tensor is expected to be anisotropic, since the planar and axial phonon frequencies for polarization perpendicular and along the c-axis direction, respectively, are different. 12,26 Employing a classical dielectric function model 20 with anisotropic phonon frequencies, the SHG signals for 4H-SiC can be calculated using Eq.…”

“…In recent years, there has been considerable interest in the mid-infrared Reststrahl 1 spectral region of Silicon Carbide (SiC), [2][3][4][5][6] since it holds much promise for a novel approach to low-loss, mid-infrared (IR) nanophotonic applications based on surface phonon polaritons (SPhPs). 4,5 Similarly to surface plasmon polaritons in metals, these surface phonon waves in the Reststrahl band of polar dielectrics can be tailored using resonant optical nano-antennas 4,5 as the fundamental building block of future nanophotonic devices.…”

“…For a detailed analysis of the experimental SHG spectra, line shape models for ε and χ (2) near the optical phonon resonances are needed. For χ (2) , Flytzanis 23 considered three different contributions containing linear, 2nd, and 3rd order terms of TO phonon resonances, which are usually denoted Faust-Henry, 24 electrical and mechanical anharmonicity, 23,25 respectively.…”