Preliminary testing
I hooked up an HP8560E to RF port of the South FSS Refl RFPD. I unlocked laser from the cavity and brought it to a place which seemed far away from any mode of the cavity.
I was hoping to see a peak at 37 MHz which is PDH modulation frequency of FSS on this path. To my surprise, signal level was ~-80 dBm only at 37 MHz. On zooming out, I saw a 29.5 MHz peak instead of about ~-55dBm. @9.5 MHz is second harmonic of the modulation frequency for South PMC PDH loop. This seemed weird as sidebands of EOM before PMC should not reach after PMC. So I have taken noted some preliminary numbers for future. This isn't complete analysis:
| Laser Slow Freq Offset (V) |
Peak Frequency (MHz) |
Peak Value (dBm) |
| -5.9975 |
0 |
-11 |
| -5.9975 |
29.5 |
-55 |
| -5.9975 |
37 |
-60 |
| -5.9875 |
0 |
-11 |
| -5.9875 |
29.5 |
-55 |
| -5.9875 |
37 |
-60 |
| -6.0275 |
0 |
-11 |
| -6.0275 |
29.5 |
-55 |
| -6.0275 |
37 |
-70 |
All data was taken with a span of 50 MHz. Note how on changing the frequency offset, I got a offset point where 37 MHz Peak almost disappears but the 29.5 MHz peak is present irrespective of the frequency. Need to investigate more.
Thu Jan 10 14:31:56 2019, in reply 2278
It is a resonant EOM. |