Nanoscale displacement sensing based on nonlinear frequency mixing in quantum cascade lasers

TL;DR

This paper presents a nanoscale displacement sensor using a quantum cascade laser with optical feedback, achieving high resolution through nonlinear frequency mixing and real-time measurement techniques.

Contribution

It introduces a novel sensing scheme leveraging QCLs' sensitivity and stability under strong feedback for nanoscale displacement detection.

Findings

Achieved { extbackslash}lambda/100 resolution in displacement measurements.

Demonstrated real-time displacement sensing with a fast-shifting reference etalon.

Discussed intrinsic measurement limits and potential for nanoscale range detection.

Abstract

We demonstrate a sensor scheme for nanoscale target displacement that relies on a single Quantum Cascade Laser (QCL) subject to optical feedback. The system combines the inherent sensitivity of QCLs to optical re-injection and their ultra-stability in the strong feedback regime where nonlinear frequency mixing phenomena are enhanced. An experimental proof of principle in the micrometer wavelength scale is provided. We perform real-time measurements of displacement with {\lambda}/100 resolution by inserting a fast-shifting reference etalon in the external cavity. The resulting signal dynamics at the QCL terminals shows a stroboscopic-like effect that relates the sensor resolution with the reference etalon speed. Intrinsic limits to the measurement algorithm and to the reference speed are discussed, disclosing that nanoscale ranges are attainable.