A high resolution interference spectroscope

Abstract

A high resolution photoelectric spectrometer employing a mechanically scanned Fabry-Perot interferometer is described. The spectrometer produces high finesse spectral profiles continuously and rapidly at repetitive frequencies of up to 1000 c/s corresponding to a time resolving limit of 4 microseconds for a scan of 5 orders.The display is on an oscilloscope or a pen-recorder function plotter. The instrument has been tested with both the high-frequency and direct current discharge spectra of mercury. Single intensity measurements are accurate and reproducible to better than 0.5%. The wavenumber scale is linear to 0.5% over an order and can be corrected to four times this accuracy. The error in determining wave number differences corresponds to one tenth of the resolving limit for a single measurement and the reproducibility is such that the r.m.s. error of ten measurements is one thirtieth of the resolving limit. Hyperfine structures agree well with recent determinations which use both pressure scanned and photographic Fabry-Perot systems. The mercury isotope abundances have been obtained from spectral intensity measurements agreeing well with mass spectrometer values. The r.m.s. deviation for a single determination is less than 0.5% of the percentage abundance. Application of the spectrometer to the study of rapidly varying phenomena in gas discharges and shock waves is illustrated by spectral profiles showing temporal intensity variations in a high-frequency discharge. Possible application to the determination of refractive indices and extension to the ultra-violet for spectroscopy from an earth satellite are briefly considered.