  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'.
