Sina, Jeff
The photodetector chassis of the LIGO-SPI pathfinder has been modified to maximize the CDS range. The TIA is designed to put out 0V - 10V on the positive leg of the differential output. The power monitoring PDs are set to get close to 5V, the interferometer PDs a mean of 2.5V, and the QPD quadrants 3.5V each. The whitening filters for the heterodyne-interferometer photodiodes are bypassed. The details of the installed capacitor and resistors are listed in the following table:
| Detector | R4 Resistor value now (kohm) | Design value of pole frequency (Hz) | C5 capacitor value calculated (F) | C5 capacitor value now (pF) | Resulting pole frequency (Hz) | Chassis Variant | Channel | Mean power at PD (mW) measured with S121C | Mean voltage at PD positive leg (V) | Sum of mean voltage of TIA positive leg (mV) | PD calibration (mW/V) |
| PD POW: FBR_PWRIN_MEAS (SIG) | 53 | 1.00E+04 | 3.00E-10 | 220 | 13,650 | 3 | 1 | 0.9 | 3.9 | 3.9 | 0.23 |
| PD POW: FBR_PWRIN_REF (LO) | 53 | 1.00E+04 | 3.00E-10 | 220 | 13,650 | 3 | 2 | 1 | 4.25 | 4.25 | 0.24 |
| QPDB | 9.9 | 13.5 | 13.5 | 0.73 | |||||||
| QPDB Q1 | 3 | 1.00E+04 | 5.31E-09 | 1,000 | 53,052 | 2 | 5 | 2.9 | 2.9 | ||
| QPDB Q2 | 3 | 1.00E+04 | 5.31E-09 | 1,000 | 53,052 | 2 | 6 | 3 | 3 | ||
| QPDB Q3 | 3 | 1.00E+04 | 5.31E-09 | 1,000 | 53,052 | 2 | 7 | 3.9 | 3.9 | ||
| QPDB Q4 | 3 | 1.00E+04 | 5.31E-09 | 1,000 | 53,052 | 2 | 8 | 3.7 | 3.7 | ||
| PD IFO: IFO_MEAS_A (LO) | 3.3 | 0.9 | |||||||||
| PD IFO: IFO_MEAS_A (SIG) | 3 | 5.00E+04 | 1.06E-09 | 1,000 | 53,052 | 2 | 3 | 4.8 | 1.29 | 2.19 | 3.7 |
| PD IFO: IFO_MEAS_B (LO) | 3.1 | 0.9 | |||||||||
| PD IFO: IFO_MEAS_B (SIG) | 3 | 5.00E+04 | 1.06E-09 | 1,000 | 53,052 | 2 | 4 | 4.8 | 1.36 | 2.26 | 3.5 |
| PD IFO: IFO_REF_A (LO) | 2.6 | 1.16 | |||||||||
| PD IFO: IFO_REF_A (SIG) | 4.99 | 5.00E+04 | 6.38E-10 | 560 | 56,955 | 2 | 1 | 2.9 | 1.24 | 2.4 | 2.29 |
| PD IFO: IFO_REF_B (LO) | 2.6 | 1.08 | |||||||||
| PD IFO: IFO_REF_B (SIG) | 4.99 | 5.00E+04 | 6.38E-10 | 560 | 56,955 | 2 | 2 | 2.9 | 1.22 | 2.3 | 2.39 |
| QPDA | 1.5 | 10000 | 1.06E-08 | 18.5 | 9 | 9 | 2.06 | ||||
| QPDA Q1 | 1.5 | 10000 | 1.06E-08 | 2000 | 53,052 | 1 | 1 | 1.9 | 1.9 | ||
| QPDA Q2 | 1.5 | 10000 | 1.06E-08 | 2000 | 53,052 | 1 | 2 | 2.6 | 2.6 | ||
| QPDA Q3 | 1.5 | 10000 | 1.06E-08 | 2000 | 53,052 | 1 | 3 | 2.2 | 2.2 | ||
| QPDA Q4 | 1.5 | 10000 | 1.06E-08 | 2000 | 53,052 | 1 | 4 | 2.3 | 2.3 |
The capacitor for the QPDs might be changed to result in a low-pass frequency of 10 kHz at a later date.