In regular operations a script called femto.py keeps the regen and e-beam timing stable to the level of ~70 fs. In this configuration the maximum delay between laser and e-beam is 10 us. Trying to change the "Target time" to more than 10 us will not result in any changes to laser timing.
To set long delays between the laser and the e-beam, the automatic correction of regen timing to e-beam needs to be disabled and all the laser triggers moved together. The triggers are moved using a python GUI. There is an apparent maximum limit of 1/360Hz = 2.78 ms delay possible between the laser and the e-beam. If you go beyond that limit you may not get what you expect.
Setting the laser up for long delays
- Disable the femto.py script by setting three toggles to “Disable” (see left)
- Change the “Time Interval Counter” reference trigger to “TRIG:LA20:LS26:TDES” to 2.8 ms. It is normally 50000 ns.
- Change the “Offset” PV to match the new value of the TIC: caput DIAG:LA20:LS22:MeasOffset 2.8e-3
- This will change the “Raw Meas.” value from ~48.7 us to ~(2.3e-3 - 1250 ns) ms. The Counter Time should still read something like 1250 ns (or whatever the Target Time was)
Changing the laser to e-beam timing
Disabling timing control in the femto.py script. This does not disable the RF lock.
The location of the Time Interval Counter trigger.
Where to find Raw Meas. timing. The offset is below to the right.