Chapter II – System Operation
2-11
C
996-0255 rev. b
E. External triggering of Precision II series
There are three methods of externally controlling the firing of the Preci-
sion II series lasers: Direct Access Triggering (DAT), Stanford Research
Pulse Generator and using the laser’s RS232 interface.
When using the DAT method, the user sends TTL signals directly to the
Precision II, bypassing the internal timing circuitry in its Control Unit
computer. Although this method requires a user-supplied TTL trigger
circuit, it reduces output jitter to ~1 ns.
With the Stanford Research Pulse Generator box, directions are given
with proper settings, page 2-13.
The third method uses your microcomputer to control the laser directly
via its RS232 interface. The asynchronous nature of microprocessor
computer programs and the RS232 interface makes it difficult to fire the
laser at a precisely known time. Details of this method, including an
example of control software, begin on page 2-15.
1) Direct Access Triggering (DAT)
DAT may be used to control all Precision series lasers, and is the pre-
ferred method of external triggering when accurate output timing (~1 ns
jitter) is critical. DAT places both the flashlamp firing and the Q-switch
opening under external control. You must supply synchronized fire
flashlamps and open Q-switch signals. DAT does not affect the Precision
II’s safety interlocks (flow, temperature, shutter, etc.).
Equipment needed:
• TTL pulse generator, producing 5 Vdc, 10 µs positive-going pulses
• two BNC cables.
Before setting up Direct Access Triggering, please review the timing
chronograph on page 2-12 and schematic 617-9900 on page 3-12. To
perform DAT:
1) Connect a cable between your external pulse generator and the
EXT flashlamp trig in BNC on the Precision’s External Trigger
Panel (ETP). The ETP is shown on page 2-14. This cable will
carry your externally supplied fire flashlamps signal.
2) Connect a second cable between your pulse generator and the
Q-switch trigger TTL BNC on the ETP. This cable will carry the
Open Q-switch signals, which will be delayed 100-600 µs from
your externally supplied fire flashlamps signals.
3) Place the ETP’s Q-switch toggle switch in its EXTernal position.
4) Set the RB601 in AUTO mode and select PGM #2. Press the
ACTIVATE key but DO NOT press the START button.
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