Enhancing methane sensors by sensing without detection

We propose a novel methane sensor based on sensing without detection. First used in quantum imaging, this technique relies on the interference effects seen in three wave mixing when pump signal and idler modes make a double pass through a nonlinear crystal. The method allows sensing at wavelengths where detectors are poor and detecting at wavelengths where photon counting sensitivity can be achieved. This compact interferometer, potentially set in a portable device for field operations, could allow the detection of low concentrations of methane at up to 100m range. Signal-to-noise ratio calculations point out that the method's sensitivity can overcome the integrated path differential absorption direct sensing at high non-linear gain regimes.