Femtosecond lasers for optical coherence tomography

Femtosecond Titanium:sapphire lasers can deliver high average power broadband spectra in a high quality beam, being therefore an optical source of choice for high-resolution optical coherence tomography (OCT) at high acquisition rates. We present a brief tutorial on the basic physics behind the operation and design of Kerr-lens modelocked lasers, where the high peak powers associated with femtosecond pulses give rise to nonlinear optical effects that play a major role in the laser operation itself and strongly influence the output spectrum. Additional nonlinear devices, in particular photonic crystal fibers (PCFs), can also be directly pumped with the generated femtosecond pulses to further extend the spectral range of the laser output, both in terms of bandwidth and center wavelength. Two specific laser systems employing different technologies for intracavity dispersion compensation (intracavity prisms in one case, and octave-spanning double-chirped mirrors in the other) will be described, and the corresponding advantages for OCT, namely the maximum achievable resolution and the applicability of spectral tuning and shaping techniques, will be briefly discussed.