Diploma

Real-time data acquisition system for laser and radio frequency spectroscopy

T. Brenner, S. Büttgenbach, T. Fabula and W. Rupprecht

Journal of Physics E: Scientific Instruments, Volume 21, Number 12

Abstract

A low-cost real-time data acquisition system utilising a master (PC-XT) and a slave (Z80) computer for high-resolution atomic spectroscopy is described. The master and the slave computer are linked by a high-speed parallel FIFO buffer permitting data acquisition on a fixed time schedule with 4 μs time resolution. A modular interface box allows the system to control complex spectroscopic experiments. The use of commercial software packages allows fast and efficient data reduction and analysis on the same computer system. The performance of the system has been demonstrated in polarisation spectroscopy experiment on zirconium.

Introduction

Spectroscopy, i.e. the study of emission and absorption of electromagnetic radiation by matter, is the main source of our information about atomic structure.

Two principle experimental techniques have been applied by our group for the investigation of atomic fine and hyperfine structure. The atomic beam magnetic resonance method in combination with state-selective laser-induced detection of rf-resonant atoms has been used to measure hyperfine structure splittings and g(J) factors of metastable states with high precision (Brenner et al 1985). In addition, Doppler-free laser spectroscopic methods have been applied to study isotope shifts and hyperfine structures of atomic transitions starting from metastable levels (Bourauel et al 1987).

In order to achieve high accuracy and sensitivity in such experiments fully computer-controlled spectrometers have to be used especially in the case of weak and/or perturbed signals. The data acquisition system of such a spectrometer should be able to control the experiment in real time and to process a large amount of data in a fast and reliable manner. In this paper we describe a versatile PC-based data acquisition system that meets these requirements.

Conclusion

A PC-based data acquisition system has been proved to be a powerful instrument for use in RF and laser spectrometers with a wide variety of applications. The system, based on an IBM-compatible PC and a Z80 slave computer (Janich & Klass), was successfully applied in high-resolution laser polarisation spectroscopy.

The realisation as a two-processor system has the advantage of a very fast system response. Data acquisition and controlling an experiment can be performed with a time resolution of at least 4 μs. Programming the system without complex interrupt handling routines is possible by virtue of the excellent real-time capability of the slave computer, a capability based mainly on the independently working FIFO-buffers. The system consists of standardised components and is widely expandable. Hardware expansions might consist of additional interface moduls (e.g. A/D-, D/A-converters) as well as replacing the PC-XT console with a PC-AT (16 bit) or even a 32-bit-technology computer with no need for further hardware modifications.

The ability to analyze the spectroscopic data immediately on the same computer is an appealing feature. Future versions of the software will utilise correlation techniques and on-line numerical analysis in order to reject bad scans and to achieve maximum data reduction. Further software improvements might also be added using commercial software packages and software tools running under the PC-DOS operating system.

Keywords

real-time data acquisition system, personal computer, laser spectroscopy, radio-frequency spectroscopy, Zirconium

Short title

Real-time data acquisition system

Acknowledgments

The authors would like to thank K. D. Krause (head of electronics lab) for his help in implementing the FORTH-kernel on the Z80 slave computer system.

References

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Published in Scientific Instruments

Authors

Thomas Brenner, Thomas Fabula, Wolfgang Rupprecht
Institut für Angewandte Physik der Universität Bonn,
Wegelerstr. 8, Bonn, Federal Republic of Germany
Stephanus Büttgenbach
Forschungsinstitut der Forschungsgesellschaft für Feingeräte-, Mikro- und Uhrentechnik e.V. (FFMU)
Breitscheidstr. 2 b, Stuttgart, Federal Republic of Germany