Throughput of tilted interferometers

The throughput of a tilted Fourier-transform spectrometer (FTS) with collimation is calculated. It is shown that the maximum off-axis angle that is acceptable in the interferometer is inversely proportional to the distance between the detector and the location where the tilt is applied to the wave fronts and is also inversely proportional to the tilt angle. This effect leads to tilt sensitivity in a scanning FTS and to the loss of the throughput advantage in a FTS with no moving part in which a tilt between two collimated beams is used to disperse the interferogram spatially. Experimental verification confirms the throughput condition with tilt angle.