Sutter Instrument SmartShutter Lambda SC, Руководство по эксплуатации

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LAMBDA SC OPERATION MANUAL – REV. 1.14C (20190606)
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14. PAIRED SHUTTERS FOR SHORT EXPOSURE TIMES
The coordinated movement of two shutters in series in the optical path can be configured to
produce shorter exposure times than is possible with a single shutter. A single shutter will
require about 8 msec with the shutter completely open before the shutter blade can start
covering the aperture. With two shutters in series this limitation can be eliminated. Starting
with one shutter open and one shutter closed, the exposure begins by opening the closed
shutter. The exposure ends when the shutter that was originally open closes. The exposure
time is determined by the delay between the start of the first shutter’s opening movement
and the second shutter’s closing movement so long as the time to open and the time to close
are essentially the same. With a reduced aperture, such as 3 mm, it takes less than 1 msec to
go from closed to open or from open to closed. There is a delay of about 5 msec between the
TTL signal and the shutter state.
If the sequence is controlled by direct commands or separate TTL signals, the timing is under
the user’s control. If the user cannot produce the direct commands or the TTL signals
required, the Lambda SC can be adapted to work with a single TTL signal. One of the
controllers is set to open on TTL high, which is the default mode of operation. The second
Lambda SC controller can then be programmed to produce a closing move on the falling edge
of the TTL command signal followed automatically by a move to reopen the second shutter.
The result with a reduced aperture, such as 3 mm, is a shutter open time that is essentially
the same as the TTL pulse duration, but delayed by about 5 msec.
Figure 14-1. Two-shutter configuration showing exposure times
For long exposure times the second shutter simply closes at the same time as the first shutter
and then reopens, so it is not required. At exposure times less than about 12.5 msec the
second shutter will begin to close as soon as the TTL line goes low. The first shutter cannot
begin to close until about 12.5 msec after the time the TTL signal went high, so if the TTL
signal goes low in less than 12.5 msec after going high, the second shutter will respond
immediately while the first shutter will not close until the 12.5 msec period is over. In other
words, while the paired shutters are capable of producing a very short exposure duration in
the sub-millisecond range, the paired shutters cannot produce high repetition rates because
the normally open shutter must have time to reset itself back to the open state before the
next exposure. The time it takes to reset should be on the order of approximately 21-24 Ms,
so the system cannot respond to a second trigger pulse in less than 21-24 Ms from the falling
edge of the preceding pulse.
In order to configure two Lambda SC controllers for this mode of operation, one controller is
operated in the default mode, which is open on TTL high. The second controller is