# Optomechanical response with nanometer resolution in the self-mixing signal of a terahertz quantum cascade laser

## TL;DR

This paper demonstrates nanometer-scale detection of mechanical vibrations using self-mixing interferometry with a terahertz quantum cascade laser, enabling high-precision optomechanical sensing and system development.

## Contribution

It introduces a novel self-mixing interferometry method with THz QCLs capable of detecting sub-wavelength mechanical vibrations with nanometer resolution.

## Key findings

- Detected vibrations with <{ extbackslash}lambda/6000 resolution
- Demonstrated potential for optomechanical system integration
- Enabled characterization of small displacements at THz frequencies

## Abstract

The effectiveness of self-mixing interferometry has been demonstrated across the electromagnetic spectrum, from visible to microwave frequencies, in a plethora of sensing applications, ranging from distance measurement to material analysis, microscopy and coherent imaging. Owing to their intrinsic stability to optical feedback, quantum cascade lasers (QCLs) represent a source that offers unique and versatile characteristics to further improve the self-mixing functionality at mid infrared and terahertz (THz) frequencies. Here, we show the feasibility of detecting with nanometer precision deeply subwalength (< {\lambda}/6000) mechanical vibrations of a suspended Si3N4-membrane used as the external element of a THz QCL feedback interferometric apparatus. Besides representing a platform for the characterization of small displacements, our self-mixing configuration can be exploited for the realization of optomechanical systems, where several laser sources can be linked together through a common mechanical microresonator actuated by radiation pressure.