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.Comment: 9 pages 4 figure