Maker's Name: 
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9.3 × 5.3 × 6.4 cm

Multiple reflections between carefully aligned partial reflectors result in narrow wavelength pass-bands when the mirror separation is an integer multiple of half-wavelengths. In this version of the Fabry Perot interferometer, called an 'etalon', the mirrors are held permanently in strict alignment by a fused silica spacer.

This unit was probably used in conjunction with a Hilger constant deviation spectrometer. Because the interference pass-bands are narrower than the linewidth of a prism spectrometer it can be used to make linewidth measurements with much higher resolution. It was purchased in 1948 for the sum of £35/10/-.

C.R.T.S. refers to the Commonwealth Reconstruction Training Scheme which provided tertiary (and other) education to returning servicemen and women.