© 2011 Thorlabs
80 Thorlabs Beam 4.0
Repetitive Pulses
This Trigger mode is helpful suited for pulsed light sources which
- provide an electrical TTL level trigger output signal
- generate pulses with duration shorter than the internal trigger delay of the
Beam Profiler
- have a constant repetition frequency, i.e. constant time interval between two
consecutive pulses,
Above diagram illustrates this case.
The laser source outputs a trigger signal "n" (rising edge) when the optical pulse "n"
is released. The pulse duration is shorter than the internal trigger delay, that's why
the appropriate laser pulse cannot be captured.
Entering the laser's repetition rate, software calculates a delay (displayed as 'Actual
Delay') to capture the next possible laser pulse - this can be the pulse "n+1" or, for
high repetition rates, "n+2", "n+3" etc.
Check ‘Repetitive Pulse’ and enter the repetition frequency in kHz within the
available range 0.001 to 50 kHz. The optimal trigger delay is calculated and
displayed.
If the repetition rate is significantly higher than 50kHz, a number of subsequent pulse
will be captured, as for this reason beam profiles of successive pulses cannot be
resolved anymore. In such cases the pulsed light source appears more and more
like a CW source. In such cases the trigger functionality can be disabled by checking
‘No Trigger’ and the external trigger signal can be omitted. In order to achieve a
constant beam power set a suitably long exposure time that performs an average
over a high number of laser pulses.
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