OCT
What is OCT and how does it work?
OCT, or Optical Coherence Tomography, is the optical equivalent to ultrasound, where the time of flight within the sample is used to obtain depth resolution. The Michelson interferometer splits the light into a reference path and an input beam to the sample via the beam splitter. Light scattered by the layers within the sample is recombined with light in the reference path at the beam splitter for detection by the spectrometer.
Light then enters the spectrometer and is collimated and redirected via a reflective collumator. Then, light is dispersed into its wavelength components using a diffraction grating. The diffracted light is focused onto the line scan array through a focusing lens. Electronic signals from the line scan array are read into the computer as data. The intensity as a function of wavelength reveals the interference between the sample and reference light. Any pathlength difference between these two light components are seen as interference fringes. These periodic spectral signals have a frequency proportional to the pathlength difference.
Signal processing is used to convert the interference signal into imaging data. The frequency components of each fringe contain information about light from a specific depth in the sample. To extract this information, each fringe is processed to produce a depth resolved reflection profile (A-SCAN). The data are first converted from wavelength (λ) to wavenumber (k = 2 π/λ) and then Fourier transformed. Each layer in the sample produces an intensity peak in the A-SCAN. When synched to our scanner by Lumedica’s custom software, a B-scan is produced showing all the layers of the sample, in real time.