Agilent Technologies 5517B Operation And Service Manual page 71

8-36. Optical Mode Tuning
Figure 8-5. Warmup Mode Timing Diagram
8-37. In optical mode, the state machine switches the subtracting sample and hold inputs from warmup feedback to
optical feedback as shown in Figure 8-6. The optical mode feedback controls the laser cavity length by measuring
and comparing the power of the two laser frequency components. Cavity length is controlled such that the difference
in power is zero. When the difference is maintained at zero, the desired characteristics of the laser beam are
established and a measurement can be performed.
8-38. The power in each laser frequency component is measured by sampling some of the laser light with a pair of
Figure 8-7)
non-polarizing beam splitters (see and passing one of the laser frequency components, then the other,
through an optical switch and onto a photodiode. The beam splitters are part of the A6 Sampler Assembly and the
photodiode is mounted on the A4 Sampler Board. A liquid crystal and a polarizer comprise the optical switch.
Figure 8-6. Feedback Loop During Optical Mode