Chapter 2 Theory of Optical Coherence Tomography
2.1 Introduction
Question 1
The coupler is assumed to split the incident optical power evenly into sample and reference arms, although many practical OCT system designs take advantage of unbalanced power splitting, as has been described both theoretically and experimentally.
Two references are cited here.
[1] Rollins, A. M. & Izatt, J. A. Optimal interferometer designs for optical coherence tomography. Opt. Lett. 24, 1484–1486 (1999).
[2] Podoleanu, A. Gh. Unbalanced versus balanced operation in an optical coherence tomography system. Appl. Opt. 39, 173–182 (2000).
These two works should be studied later.
2.2 Confocal Gating and Lateral Resolution in OCT Systems
Question 2
Even for OCT systems that do not employ fiber optics, the antenna response function of the homodyne wave mixing inherent to OCT can be shown to be equivalent to confocality.
Check this work below:
[1] T. Sawatari, Optical Heterodyne Scanning Microscope, Appl. Opt. 12, 2768-2772 (1973)
Question 3
Confocal microscopes have the advantage of slightly improved lateral resolution over conventional bright-field microscopes and the ability to perform “optical sectioning” due to their peaked axial response.
Remind yourself of the principle of confocal microscopy.
Question 4
What is a f-theta scanning system?
Check this article below:
How F-Theta Lenses work ( & when to use one)
Question 5
What is confocal gate length?
2.3 Spatial Coherence Gating in Full-Field OCT Systems
Question 6
Fourier-domain FFOCT has only been demonstrated using swept sources since a three-dimensional camera would be necessary to obtain the two spatial and one spectral dimensions that would be required for spectrometer-based spectral-domain FFOCT.
Is it true now?
Question 7
Cross talk artifacts can be avoided by employing a light source with low spatial coherence [1].
Check this work below:
[1] B. Karamata, P. Lambelet, M. Laubscher, R. P. Salathé, and T. Lasser, Spatially incoherent illumination as a mechanism for cross-talk suppression in wide-field optical coherence tomography, Opt. Lett. 29, 736-738 (2004)
Question 8
The author mentioned that the thermal sources have the limitation of low speed and sensitivity, two methods have been proposed, including reducing the spatial coherence of a coherent source [1], and using lasers with moderate temporal coherence and low spatial coherence [2].
Need to check these works:
[1] A.H. Dhalla, J.V. Migacz, J.A. Izatt, Crosstalk rejection in parallel optical coherence tomography using spatially incoherent illumination with partially coherent sources. Opt. Lett. 35(13), 2305–2307 (2010)
[2] B. Redding, M.A. Choma, H. Cao, Speckle-free laser imaging using random laser illumination. Nat Photon 6(6), 355–359 (2012)
2.4 Axial Ranging with Low-Coherence Interferometry
Question 9
Is there any simply explanation of spatial and temporal frequency?