# White light interferometer

I am building white-light Michaelson interferometer and I am registering interference in frequency domain via spectrometer. I read an article, where the same is done (just Mach-Zender interferometer) and it is said, that Fourier trasform gives direct access to absolute path-length difference:

But if we apply Fourier transform to spectra (x axis is frequency in Hz), Fourier transform will gives us something in seconds (1/Hz), not in meters. My question is, how it is done here? Is "seconds" axis multiplied by c (light speed), or something different is applied? What relation is used here?

Article reference: Attosecond beamline with actively stabilized and spatially separated beam paths M. Huppert, I. Jordan, and H. J. Wörner http://dx.doi.org/10.1063/1.4937623

• could you provide a reference for the article? Apr 19, 2021 at 10:36
• Yes, I should have added reference to main question too. Attosecond beamline with actively stabilized and spatially separated beam paths M. Huppert, I. Jordan, and H. J. Wörner dx.doi.org/10.1063/1.4937623 Apr 20, 2021 at 16:35

Yes, the fact that light travels at speed $$c$$ is implicit in the conversions between units here. What you’re actually measuring is an interferogram with $$x$$ (the mirror position) as the independent axis. Then to convert to frequency, you’ll need to include $$c$$ in your calculation. And don’t forget that in a Michelson interferometer, a change of mirror position $$x$$ corresponds to a change in light path length of $$2x$$!