Mid-infrared Assisted THz Phonon Amplification in a 2D Semiconductor for Room Temperature Detection

TL;DR

This paper introduces MIRAPA, a mid-infrared-assisted method for efficient, room-temperature phonon amplification in 2D semiconductors, enabling sensitive vibrational detection and potential phonon device applications.

Contribution

The study presents a novel MIRAPA technique that directly couples MIR light to lattice vibrations, achieving high amplification with low power and long-term stability in 2D materials.

Findings

Room-temperature phonon amplification exceeds 80% using MIRAPA.

MIR power density is nearly 300 times lower than visible excitation for similar effects.

Phonon modulation persists over 2800 cycles and 15 hours without degradation.

Abstract

Efficient and selective excitation of lattice vibrations is central to controlling energy flow at the nanoscale, yet remains challenging under conventional optical excitation. Here, we introduce a mid-infrared-assisted phonon amplification approach, termed MIRAPA, that enables efficient energy injection directly into vibrational bonds. Using surface-enhanced resonant Raman scattering in few-layer $\mathrm{MoS_2}$, we exploit strong exciton--phonon coupling to monitor phonon populations. When mid-infrared (MIR) light is introduced, it couples directly to out-of-plane lattice vibrations, leading to room-temperature phonon amplification exceeding $80\%$. Crucially, MIRAPA bypasses electronic excitation pathways, allowing the MIR power density to be nearly $300\times$ lower than that required for visible excitation to achieve comparable enhancement. The resulting phonon modulation is robust, persisting over more than $2800$ on/off cycles and exceeding $15$ hours of continuous-wave laser illumination without degradation. Quantitative analysis yields an effective noise-equivalent power of approximately $0.3\,\mathrm{nW}/\sqrt{\mathrm{Hz}}$ for MIR detection, highlighting the sensitivity of the approach. By combining vibrational selectivity, low-power operation, and long-term stability, MIRAPA provides a robust platform for probing and amplifying phonons in two-dimensional semiconductors. These results open new opportunities for nanoscale vibrational sensing, mid-infrared detection, and phonon-based coherent devices, including routes toward phonon lasing.