SS-OCT System Base Unit
Chapter 4: System Operation
Page 32
MTN013142-D02
4.3.2. Imaging through Refractive Media
To acquire OCT images, the optical path lengths of the sample arm and reference arm have to be matched.
When imaging through refractive media,
The optical path length of the sample arm is increased, which has to be compensated in the reference
arm (for more details see chapter 5.6).
The amount of dispersion changes, which can be compensated using the ThorImageOCT software.
Every time the amount of refractive media is changed, this procedure has to be repeated in order to achieve a
good image quality.
Figure 40
Step by Step Adjustments when Imaging through Refractive Media
Instead of adjusting focus and reference arm length at the same time, it is often helpful to first find the focus
and then adjust the reference arm length. Figure 40 shows this procedure step by step, starting with a sample
that is out of focus and with a misaligned reference arm, so that no sample can be seen in the B-scan (Figure
40 A). After finding the focus, autocorrelation terms will appear in the upper part of the image even without any
reflecting surface in the field of view of the B-scan. When these artifact signals are the strongest stop focusing
and adjust the reference arm length so that the image appears in the top half of the window.
Furthermore, the refractive media will introduce dispersion effects, i.e. washing out due to a dependence of the
phase velocity on the wavelength. This can be compensated using the ThorImageOCT software (for more
details see the software manual). Note that the amount of dispersion depends on the thickness of the refractive
media, hence, the dispersion compensation has to be changed every time the thickness of the refractive media
is changed.
Note: If you are able to identify autocorrelation signals but are not able to move the OCT image into the
observable window, the optical path length of the sample arm is likely increased to an extent that cannot be
adjusted by the reference arm anymore. Thorlabs offers a special reference arm adapter to further increase the
reference arm length, please contact Thorlabs for more information.
Autocorrelation
Signals
A
B
C
D
