Laser Medicine and Medical Imaging

Optical coherence tomography (OCT) is an emerging technology for micron-scale cross-sectional imaging of biological tissue [1, 2]. Enhancing the resolution of OCT images continues to be a very active field of research. The longitudinal resolution in OCT images is inversely proportional to the optical bandwidth and proportional to the square of the center wavelength of the light source. Ultrahigh resolution OCT requires extremely broad bandwidths because of this λ/∆λ dependence of the longitudinal resolution. This is particularly the case for the spectral region between 1.2 μm and 1.5 μm. This spectral region is of high interest for OCT because of the high penetration depth in biological tissue and the possibility of performing spectral resolved imaging of water absorption bands. Superluminescent diodes are used in conventional OCT systems and typically yield 10-15 μm longitudinal resolutions. We demonstrated previously OCT imaging with resolutions of 1 μm at 800 nm [3] and 5.1 μm at 1300 nm [4] in biological tissue using a Kerr-lens mode-locked Ti:sapphire laser with double-chirped mirrors and the self phase modulation broadened spectrum of a Kerr-lens mode-locked Cr:forsterite laser, respectively.