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Contrôle informatique
The experiments may involve comples sequences, with a few thousand atomic samples, each undergoing selective state transformations in the Ramsey zones and in the cavity. The whole experiment is controlled by a dedicated computer software.
This software has been primarily developed by S. Kuhr (now at Mainz university) during his post doctoral stay in our group. It is written in C in the LabWindows National Instruments development environment. The interface with the experiment is realized with Natinst boards.
The software gives a complete control over the experimental sequence. All events (laser and microwave pulses, electric field pulses, circularization processes) can be timed with a 10 ns resolution. The sequence may involve an arbitray number of atomic samples. Each sample may undergo fully tailorable transformations in the Ramsey zones. The ’static’ electric field in the cavity is also under software control. It makes it possible to adjust in real time the atom-cavity resonance condition via the Stark effect.
The experimental sequence definition can be stored and retrieved, making it possible to switch from an experiment to another in the matter of seconds. This is particularly useful when switching from actual data taking to calibration sequences.
The programmed sequence is uploaded in the timing board and is then run independently from the computer. It ensures a precise timing, idependent on the computer load/interruptions.
During the sequence, all detected electrons are time-labelled and stored by a dedicated board. At the end of the sequence (or at the end of a few repetitions of the sequence) these data are downloaded in the computer memory. The precise timing makes it possible to attribute each electron to a precise atomic sample and to a definite level in the time-resolved detection mode.
These data are processed by the computer and displayed in real time, while the next sequence is run by the boards. All individual detection events are stored on the computer disk for later data analysis. It is thus possible to change the data interpretation algorithms long after completion of the experiment.
This extremely flexible software interface has been instrumental in the recent QND photon detection experiments, which require extremely complex sequences.
Additional softwares are used to control the cryogenic set-up (temperature measurements or liquid helium transfer) and the various laser locks. These softwares, all running on the same multi-processor machine, are interfaced together. When a laser unlock condition is detected, for instance, the data acquisition is halted and resumes automatically when the lock is restored.
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