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Fourier Domain Mode-Locking (FDML): Wavelength swept lasers for biomedical imaging, optical sensing and profilometry

Dr. Robert Huber, LMU

The mechanism of Fourier Domain Mode Locking (FDML) is a new, stationary operating regime of lasers, complementary to standard mode locking techniques. In FDML, not the phase or amplitude but rather the spectrum of the light inside a kilometer long laser cavity is modulated synchronously to the optical roundtrip time, resulting in the emission of rapid, narrow band wavelength sweeps. Using FDML lasers for optical coherence tomography (OCT) in biomedical imaging, it is possible to achieve unprecedented imaging speeds. Tissue properties like birefringence and flow dynamics can be visualized by polarization sensitive OCT and Doppler OCT. In optical sensing applications the high phase stability of FDML lasers enables high-speed profilometry with sub-nanometer resolution. The concept of FDML, its applications for OCT imaging and sensing as well as future developments are discussed.