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Optical Coherence Tomography

Using ECOPS to speed up TD-OCT measurements

  • Time-domain OCT
  • Ultra-broadband: 1000 nm – 1500 nm
  • Low modulated spectra
  • OCT resolution < 15 µm @ 1560 nm
  • Optical sampling (ECOPS)

Originally developed for ophthalmology, Optical Coherence Tomography (OCT) now spreads over to a variety of applications. The benefit of this technique is the imaging capability of sample structures even at a few millimeters depth with micrometer resolution. For example, invisible defects lying underneath the surface of manufactured parts or different layers in biological tissue and in medieval paintings can be visualized. OCT relies on low coherence interferometry utilizing spectrally broad light sources like superluminescent diodes or femtosecond lasers, since the resolution of OCT is determined by the inverse bandwidth of the light source. Different techniques are competing today: time domain OCT (TD-OCT) and frequency/spectral domain OCT (SD-OCT). While TD-OCT exhibits a huge imaging depth it is limited in recording speed. Complementary, SD-OCT excels in recording speed but lacks the large imaging depth.

TOPTICA combines the advantages of both techniques in a newly developed optical sampling method: Electronically Controlled Optical Sampling (ECOPS). ECOPS speeds up TD-OCT measurements by several orders of magnitude avoiding movable parts in the set-up: two femtosecond fiber lasers are synchronized. Both pulse trains have a determined phase shift in respect to each other. This corresponds to a fixed scan position in TD-OCT. Varying the control voltage of the synchronization unit, this phase delay can be scanned with several hundred Hertz closing the gap to SD-OCT. The imaging depth remains large and the scan can be hold on any position or zoomed in on interesting features in the OCT image.