PRECISION ANGLE MEASUREMENT IN A DIFFRACTIONAL SPECTROMETER BY MEANS OF A RING LASER

The measurement of radiation diffraction angles in spectrometers is us ually carried out by means of optical encoders or laser interferometer s. An angle measurement system based on a ring laser (RL) is described in this paper. The main feature of the RL is that a standing electrom agnetic wave in the RL cavity can be considered as a high-precision ci rcular scale. Systems incorporating RLs usually provide an accuracy of angle measurements of several hundredths of an arcsecond in the measu rement range 0-360 degrees. The system described here consists of a RL and an optical interference null-indicator located on a rotary platfo rm optically connected to the crystal of the diffractional spectromete r. An analysis of the measurement principle and measurement errors is presented. It is shown that the main sources of error are the random d rift of the phase of the RL output signal and the wideband fluctuation of the null-indicator output signal. Results of measurements of the x -ray line of K-alpha Mo-1 radiation with an energy of radiation E = 17 .47334 keV and corresponding wavelength lambda = 0.71 Angstrom are sho wn. The angle measurement error of the described system turned out to be about 0.05 arcsecond.