THORLABS Redstone OSA302 Manual page 21

Optical Spectrum Analyzers Chapter 5: Using the Free-Space Input
Figure 11. Alignment Beam Activation and Notification for OSA20xC Models
The Redstone OSA30x instruments also include a red alignment laser, which will exit the free-space port when
activated with a button in the "Free-space Alignment" window (see Figure 12). When the alignment beam is
activated, one optical arm of the interferometer is blocked and no interferometric measurements can be
performed, and a warning message will appear in the ThorSpectra software. However, the second optical arm
is not blocked and light from this arm is incident on the detectors. The "DC signal" of the detectors is available
when the alignment beam is activated and can be of assistance in the alignment process.
Note that when the "Free-space Alignment" window is open, the detector offset is disabled and the saturation
level is decreased. When clicking the "Done" button to close the window, the autogain algorithm will try to find
gain and offset settings that optimize the interferogram signal.
Figure 12. Alignment Beam Activation for the Redstone OSA30x Models
The unknown input should be adjusted to be collinear to the alignment beam for optimal measurement accuracy.
To begin the procedure of aligning an external free-space light source, turn on the alignment beam and proceed
with the alignment, following the instructions in Section 5.3.1. Clicking the "Help" button in the "Free-space
Alignment" window in Figure 12 will open a PDF file with a tutorial with further details and examples.
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