Correct trigger levels are crucial for a correct operation of the Time Tagger software module.
To adjust the trigger levels, open the device settings window via the menu bar => Device => Hardware settings
Make sure that the channel number settings matches the input connections at the hardware. Subsequently, adjust the trigger levels of each channel. To check the settings, activate the Check trigger levels button at the bottom of the window. Not in the counts/s row, the current countrates of each channel are displayed. Check if the countrates match the input signals:
- Start signal: Repetition of the pulse generator
- Stop signal: Bring the TFPI into reflection/alignment mode and check the signal intensity. Note: the expected countrate depends on the scanning speed (ms/channel) of thaTEC:TFPDAS! Example: overall intensity: 400 counts/channel and scan speed 1 ms/channel => expected average countrate: 400.000 counts/s
- Counter: With thaTEC:TFPDAS in measurement mode (spectrum is being acquired), the countrate of this channel should match half the scanning speed (ms/channel). Please note that during the retract of the interferometer mirrors, no signal is applied to this channel reducing the expected average countrate. Example: scan speed 1 ms/channel => expected average countrate: 500 counts/s.
- Reset: The trigger level should be the same as for the counter channel. The expected countrate should match the rate of acquired scans of thaTEC:TFPDAS during a measurement.
- Gate: The trigger level should be the same as for the counter and the reset channel and also match the rate of acquired scans of thaTEC:TFPDAS during a measurement times the number of (non overlapping) ROIs. Example: thaTEC:TFPDAS is scanning with a speed of 1 scan per second and there are 2 ROIs => Expected countrate: 2 counts/s.
Even if the count rates (in particular for the stop channel/detector) match the expectations, a too low value might result in a wrong timing since some pulses might be detected earlier than others due to variations of the pulse shape. Thus, always check if the acquired signal matches the expectations. Below, the result for a 50 ns long pulsed excitation is shown with incorrect (left) and correct (right) trigger level settings displaying the effect on the acquired data.