> Frequency-sweeping... How are you doing that?
A much more thorough description is found in the paper that introduced FDML for the first time:
> Is the laser itself able to frequency sweep?
> Or are you chirping pulses?
What you're doing sounds a lot like time-domain spectroscopy in an odd sort of way.
What are the advantages of this versus just chirping a pulsed supercontinuum source?
> What you're doing sounds a lot like time-domain
> spectroscopy in an odd sort of way.
> What are the advantages of this versus just
> chirping a pulsed supercontinuum source?
Sweep uniformity: The phase evolution of the sweeps is very stable; the mean deviation in phase differences between sweeps is in the order of millirad. Which means that for the time→k-space mapping the phase evolution has to be determined only one time and can then be used for hours of operation; in fact the system operates to repeatable that even after being powered off over the night, the next morning you can often reuse the phase calibration of the previous day. Without that, you'd have to use a second interferometer and sample a k-space reference signal for each and every sweep in parallel and use that for k-space remapping.
Ease of synchronization: Trigger signals have very small jitter. Also the jitter between electrical and optical synchronization is in the order of few ps, which is important for things like Doppler-OCT.
Coherence: Supercontinuum Sources have issues with coherence stability, which degrades the imaging range.
Sentisivity issued: Chirping Pulsed Supercontinuum Sources (which are actually used for OCT) is challenging. It requires a lot of dispersion. High dispersion means a lot of loss, which in turn means it requires another output amplification stage, which in turn will also produce significant optical noise. And optical noise is the bane of OCT, since that reduces the sensitivity. In contrast to that if properly dispersion compensated an FDML laser will exhibit very little noise.
Price: Pulsed Supercontinuum Sources suitable for chirping and OCT applications are quite expensive. Our laser is not cheap as well, but it's still more price effective.