THORLABS OCTP Series User Manual page 30

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6. Align the optical beamsplitter module with respect to the reference arm module. The goal of this step is
to maximize the intensity of the light in the reference arm that returns to the collimator and is collected by
the fiber. To monitor the power in the reference arm, use the reference light intensity monitor as shown
in Figure 30. It turns red if the camera is saturated by the reference light. Then, the iris needs to be closed
to reduce the reference intensity.
No Reference Intensity
Optimum Reference Intensity
Before starting adjustment of the beamsplitter, loosen the locking screw of the micrometer and tighten the
fine adjustment screw of the rotation plate. Note that overtightening the fine adjustment control screw may
prevent proper operation of the micrometer driven stage. Use the knob and hex slot indicated in Figure
31 to align the optical beamsplitter module such that the beam going into the reference arm module is
centered on the reference arm mirror. (It should not be necessary to use the hex slots that are not
indicated.)
Align the beamsplitter for maximum intensity. If the display reaches its limit (very high reference light; see
Figure 30), it does not necessarily indicate that maximum intensity is being collected by the fiber; it can
simply indicate that the intensity exceeds the dynamic range of the detector. If this occurs, use the variable
aperture (and/or select a higher A-scan rate in ThorImage
usable dynamic range, then continue aligning the beamsplitter to see if the intensity can still be increased.
Use both the aperture and the beamsplitter iteratively to maximize the back reflected light.
7. After changing the beamsplitter orientation, it is necessary to check the centration of the beam on the
alignment target. If the beam through the objective aperture is not well centered along an optical axis (i.e.,
the beam is coming out at an angle), it is necessary to repeat steps 5 and 6 iteratively.
8. Close the ThorImage
light indication LED at the base unit is no longer lit. Remove the alignment target and re-install the
objective and illumination part.
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Very Low Reference Intensity
High Reference Intensity
Figure 30 Reference Light Intensity Monitor
Figure 31 Adjustment of Beam Splitter
®
OCT software to turn off the light source in the OCT base unit. Check that the SLD
Low Reference Intensity
Very High Reference Intensity
®
OCT) to return the measurement within the
Chapter 4: Installation
MTN003971-D02