En-face scanning optical coherence tomography with ultra-high resolution for material investigation.

Optical coherence tomography (OCT) is an emerging technique for cross-sectional imaging, originally developed for biological structures. When OCT is employed for material investigation, high-resolution and short measurement times are required, and for many applications, only transversal (en-face) scans yield substantial information which cannot be obtained from cross-sectional images oriented perpendicularly to the sample surface alone. In this work, we combine transversal with ultra-high resolution OCT: a broadband femto-second laser is used as a light source in combination with acousto-optic modulators for heterodyne signal generation and detection. With our setup we are able to scan areas as large as 3 x 3 mm2 with a sensitivity of 100 dB, representing areas 100 times larger compared to other high-resolution en-face OCT systems (full field). We demonstrate the benefits of en-face scanning for different applications in materials investigation.