Agilent Technologies 5517B Operation And Service Manual page 72

Figure 8-7. A6 Sampler Assembly, Exploded View
8-39. When the state machine excites the liquid crystal into its active state (see Figure 8-8), the laser beam passes
through the liquid crystal unaltered. The polarizer blocks the horizontal component and passes the vertical
component onto the photodiode. The photodiode current is proportional to the power in the vertical component and is
amplified and converted to a voltage by the photodiode amplifier. The voltage is held on the positive input of the
subtracting sample and hold circuit.