This work is on 20220303.
I measured CCFC error signal with green 1/f, 1/f^4 filters, and CCFC. The green transmission beam spot is upper side of camera (new beam spot). The green FC injection power was 23mW. The parameters for 1/f and 1/f^4 filters are as follows. Fig 1 shows the green OLTF.
| filter | input attenuator | piezo gain | UGF |
| 1/f | 0.8 | 8 | 11 kHz |
| 1/f^4 | 0.2 | 8 | 13 kHz |
The measured CCFC error signal with green 1/f, 1/f^4 filters, and CCFC are shown in Fig. 2. The CCFC amplitude was 142mVpp. CCFC filter gain is 1000 with 30Hz LPF.
Measurement of CCFC OLTF
CCFC OLTF can be measured by injecting a signal to sum port of CCFC filter (SR560) and measuring CCFC filter input/output. The relation between this measurement and CCFC OLTF is as follows.
(CCFC filter input/output)*CCFC filter = - G_CCFC/(1+G_green)
G_CCFC = - (CCFC filter input/output)*CCFC filter*(1+G_green)
Since the CCFC filter and G_green are known, G_CCFC can be obtained. Fig. 3 shows green, CCFC OLTF. The crossover frequency between green/CCFC is 1.6kHz.
