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

1. Disable the femto.py script by setting three toggles to “Disable” (see left)
   
2. Change the “Time Interval Counter” reference trigger to “TRIG:LA20:LS26:TDES” to 2.8 ms. It is normally 50000 ns.
3. Change the “Offset” PV to match the new value of the TIC: caput DIAG:LA20:LS22:MeasOffset 2.8e-3
   1. 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

Open the long laser timing GUI:

Select "Enable Tracking" and update the target time as you see fit. Note this GUI is under construction.

Restoring normal timing operations

1. Change the “Offset” PV to 50 us: caput DIAG:LA20:LS22:MeasOffset 50.0e-6
2. Change the “Time Interval Counter” reference trigger to “TRIG:LA20:LS26:TDES” to 50 us (50000 ns).
3. Re-enable the femto.py script by setting three toggles to “Enable” (see left, at the top)
4. Recalibrate the laser timing. See "When I change the target time the counter time changes, but by the wrong amount" under Adjusting Laser Electron Beam Timing