SS-OCT System Base Unit
Chapter 4: System Operation
Rev A, December 17, 2018
Page 27
4.2.
Basic Adjustments
When receiving the SS-OCT system from Thorlabs, the reference length is adjusted so that OCT imaging in air
is possible simply by adjusting the focus to the region of interest. If the reference arm length no longer matches
the sample arm length, the following procedure will aid you to a good basic adjustment. For OCT imaging
through refractive media, e.g. water or glass, please refer to chapter 4.3.2.
4.2.1. Adjusting the Focus
For a coarse adjustment of the focus, place a suitable sample, e.g. the IR viewing card delivered with the
system, underneath the scanner. Using the OCT software, a fraction of the card can be seen in the sample
monitor. Now adjust the height of the imaging scanner with respect to the card by adjusting the focus block of
the OCT-Stand (see Figure 32) to obtain a sharp image.
Figure 32
Basic Focus Adjustment
4.2.2. Adjusting the Reference Length
The Vega Swept Source OCT System is preset so that the “zero-delay” line is set to a depth position of 0 mm.
This means that when the surface of the sample under test is placed in the focus of the objective in use, it will
be shown at 0 mm of the imaging depth. However, in case of any misalignment due to shipping, etc., corrections
can be made by adjusting the length of the reference path. Also, when using a different objective, the reference
path length will have to be changed accordingly. The reference path in the Vega system is motorized and
controlled through the GUI (ThorImageOCT) as indicated in Figure 33.
Figure 33
Reference Length Controls
For detailed information, please refer to the respective Software Manual section (Chapter 3: OCT Imaging
3.1 Reference Length). Adjustment of the reference length may be done in combination with focus height
adjustment (using the OCT stand), so that the focus position in the OCT data is shifted. Also, this adjustment is
necessary when imaging in a refractive material.
The following steps will guide you to a basic adjustment of the reference length:
Start B-scan acquisition. When significantly misadjusted, you will get an incorrect OCT image or no
image of your sample, irrespective of the focus position.
off focus
in focus
