THORLABS GAN1x1 Series, Руководство пользователя

Страница: 39 / 80

SD-OCT Base Unit Chapter 4: System Operation
Rev C, June 25, 2021 Page 35
Optimizing the Sensitivity
In Frequency Domain OCT systems, a decrease in sensitivity is observed at larger measurement depths. This
is especially obvious in SD-OCT systems where this so-called roll-off already starts to affect measurements at
around 30% of the maximum measurement depth. For example, the contrast of the structure in Figure 37D is
much better than in C, even though the only difference is its position in depth. Keeping the region of interest in
the top half of the imaging window to use the most sensitive region of the instrument is therefore advised.
For some measurements it is not possible to keep the region of interest in the top half of the window,
e.g. because there is additional material on top of the region of interest that would flip back into the image and
overlay with the region of interest. In those situations, it might be helpful to flip the whole image of the sample
(see chapter 5.6). Note that you can use the software to flip the image back to its original position, however, this
is purely cosmetic and does not increase the sensitivity (for more details see the ThorImage
®
OCT software
manual).
Figure 38: Measured Sensitivity Roll-Off (GAN621 & TEL221)
Figure 38 summarizes the roll-off measured for two typical base units, the GAN621and the TEL221. The depth
of each graph is normalized to the respective maximum measurement depth.
0 20 40 60 80 100
-10
-8
-6
-4
-2
0
GAN621 Roll-Off
Sensit
ivit
y Loss (dB)
Rel. Image Depth (%)
0 20 40 60 80 100
-10
-8
-6
-4
-2
0
TEL221 Roll-Off
Sensitiv
ity Loss (dB)
Rel. Image Depth (%)