A computerized data acquisition and control system for Fabry-Perot inteferometry

Tong, Shidong (1990) A computerized data acquisition and control system for Fabry-Perot inteferometry. Masters thesis, Memorial University of Newfoundland.

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Abstract

Fabry-Perot interferometry is one of the most powerful techniques in high resolution spectroscopy, especially in Raman and Brillouin scattering. Proper operation of a Fabry-Perot interferometer presumes the Fabry-Perot plates to be maintained in parallel alignment for a reasonable period of time while the experiment is in progress. Misalignment and laser frequency drift can cause very serious losses of finesse, and therefore of resolving power and contrast. -- Various methods of stabilizing the interferometer system have been reported previously. May et al. described a data acquisition and stabilization system for the Fabry-Perot interferometer which automatically compensates for all instrumental frequency drifts, maintains interferometer alignment, and permits extended data acquisition time in selected spectral regions of interest. The commercial version of this data acquisition system is known as DAS-1. It was originally produced by Burleigh Instruments, Inc. in 1976 and has been the accepted standard among commercially available instruments. However it has not been available for several years. -- Hardware and software packages which perform multichannel scaling (MCS) are now commercially available from several sources. The ACE-MCS package as supplied by EG&G-ORTEC and used in the present work consists of an IBM PC plug-in card and an MCS emulation program. This ACE-MCS package is simple and easy to use, but it lacks some essential features required in Fabry-Perot interferometry. The main problem is that it does not permit active feedback control of the interferometer alignment. In addition, it does not provide for a segmented ramp-voltage output, which is necessary in situations where the scattered light is very weak. -- In order to adapt this MCS package for Fabry-Perot interferometry, it was consequently necessary to modify and augment the hardware and software to accommodate the following functions: drift stabilization, finesse optimization, segmented ramp scanning. -- The drift stabilization and finesse optimization functions mainly required software development, while segmented scanning required hardware development in the form of a digital electronic circuit. -- A prototype system, based on an IBM-XT clone, has been developed at relatively modest cost and has been tested to record Brillouin scattering spectra of fused quartz. The experimental results show that the system is able to maintain Fabry-Perot alignment as well as the original Burleigh DAS-1 system.

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