I try to get a clear understanding of FTIR spectroscopy and it is unclear to me what exactly the interferogram shows. I know that we see the intensity of the superpositioned beams where we vary the path length of one beam via a moveable mirror. But what kind of intensity do we talk about there? Is it the instantenious intensity or is it some time averaged intensity?
Is the moveable arm moved step by step and at each position the signal is averaged for this position to give one data point, Or does the arm continuously move and we measure a more or less continuous intensity signal as the arm moves?
An example of an FTIR interferogram, from here: