> You basically have a very fast laser that
    > can do volumetric scans at a high framerate,
    > did I get this right?

Sort of. The laser itself is constantly sweeping its wavelength (over a bandwidth of >100nm). Using it as a light source in a interferometer where one leg is reflected by a fixed mirror and the other leg goes into the sample something interesting happens: The interferometric fringes produced for a certain wavelength correspond to the spatial frequency of scattering in the sample. So the fringe distribution over wavelengths is the Fourier transform of the scattering distribution. So by applying an inverse Fourier transform to the wavelength spectrum of the light coming out of the interferometer you get a depth profile.

Now the challenge is to get the wavelength spectrum. You can either use a broadband CW light source and a spectrometer. But these are slow, so you can't generate depth scans at more than about 30kHz (which is too slow for 3D but suffices for 2D imaging). Or you can encode the wavelength in time and use a very fast photodetector (those go up to well over 4GHz bandwidth).

This is what we do: Have a laser that sweeps over 100nm at a rate >1.5MHz and use a very fast digitizer (1.8GS/s) to obtain a interference spectrum with over 1k sampling points. Then apply a little bit of DSP (mapping time to wavelength, resampling, windowing, iFFT, dynamic range compression) and you get a volume dataset.

BTW, all the GPU OCT processing and visualization code I wrote, too.

    > What do people typically use it for?
	

Mostly for OCT, but you can also use it for fiber sensing (using fiber optics as sensors in harsh environments), Raman spectroscopic imaging, short pulse generation and a few other applications. But OCT is the bread and butter application for these things.