Fig. 7: High-frequency detection circuit.
From: A system for probing Casimir energy corrections to the condensation energy
The cryostat is held at a constant temperature just below Tc on the slope of the transition. The high-frequency Vdrive signal is applied to the drive electrode and swept at frequency f2. The plate then feels an electrostatic force at frequency 2f2. The amplitude of the plate is monitored by measuring the AC current going through the sense electrode using a current-to-voltage amplifier and a lock-in referenced to 2f2 (LIA 1). The voltage drop across the Pb sample is also detected at 2f2. If there is any change in Tc due to the Casimir cavity size, then this is the frequency at which it would occur. Because the excitation current, Iex, is alternating at f1, the DC output of LIA 2 is fed into a third lock-in, LIA 3, which is referenced at f1
