Sub-wavelength mid-infrared imaging of locally driven photocurrents using diamond campanile probes

TL;DR

This paper presents a diamond-based campanile probe that efficiently concentrates mid-infrared light into sub-wavelength volumes, enabling high-resolution mapping of photocurrents in graphene with significant enhancement and coupling efficiency.

Contribution

Introduction of a novel diamond campanile probe for sub-wavelength mid-IR imaging, improving light concentration and photocurrent mapping in 2D materials.

Findings

Photocurrent signal density enhanced by 10^3 times.

Coupling efficiencies approach 80%.

Probe operates effectively with quantum cascade and free electron lasers.

Abstract

Precise and high efficiency concentration of mid-infrared (mid-IR) light into sub wavelength volumes is essential for probing low-energy excitations and achieving strong field enhancements, which can be hindered by absorption losses and coupling inefficiencies at long wavelengths. Here, we introduce an innovative diamond-based metal-insulator-metal campanile probe that adiabatically compresses free-space mid infrared light (10 \mum) into \approx 1 \mum domains. Integrated into a scanning photovoltage microscope, the probe enables sub-wavelength mapping of locally driven photocurrents in graphene, resolving polarization dependent and contact-sensitive responses at energies down to \approx 0.1 eV. Experiments reveal a photocurrent signal density enhancement of 10^3 and coupling efficiencies approaching 80%, in agreement with numerical simulations. Operation of the probe with quantum cascade and free electron lasers demonstrates a robust, spectrally tunable platform for high-resolution exploration of low-energy carrier dynamics in atomically thin materials, opening opportunities for mid-IR optoelectronics and quantum photonics.