Loss compensated and enhanced mid-infrared interaction-free sensing with undetected photons

TL;DR

This paper demonstrates a novel mid-infrared sensing technique using undetected photons that achieves high sensitivity and interaction-free operation, enabling detection of extremely low power signals at 3.4 μm wavelength with immunity to thermal background.

Contribution

It introduces a loss-compensated nonlinear interferometer for mid-infrared sensing with undetected photons, achieving enhanced sensitivity and interaction-free operation.

Findings

Recovered sensitivity despite internal losses.

Detected attowatt-level signals at 3.4 μm wavelength.

Achieved immunity to thermal black-body background.

Abstract

Sensing with undetected photons enables the measurement of absorption and phase shifts at wavelengths different from those detected. Here, we experimentally map the balance and loss parameter space in a non-degenerate nonlinear interferometer, showing the recovery of sensitivity despite internal losses at the detection wavelength. We further explore an interaction-free operation mode with a detector-to-sample incident optical power ratio of >200. This allows changes in attowatt levels of power at 3.4 $\mu$m wavelength to be detected at 1550 nm, immune to the level of thermal black-body background. This reveals an ultra-sensitive infrared imaging methodology capable of probing samples effectively `in the dark'.