GB312534A - Construction of a fabry perot interferometer (etalon) - Google Patents

Abstract

312,534. Williams, W. E. July 11, 1928. Interferometers.-Optical interferometers of the reflection echelon or the Fabry Perot etalon type have the separation between successive reflecting surfaces maintained substantially constant by making the plates (in the one type) or the spacing means (in the other type) of fused silica or other material having a negligible coefficient of thermal expansion, the contacting surfaces being in optical contact. The echelon plates 1 are optical worked until plane parallel to a high degree of accuracy and are placed in optical contact, being but lightly held in a clamp comprising end plates 2 and rods 3 with nuts 4. The rods are of invar steel and the thickness of the washers 5 is chosen so that the resulting thermal expansion is the same as that of thet plates. The steps 6 are metallized by cathodic deposition. The two plates, 13, 14, Fig. 2, of the Fabry Perot interferometer are, spaced apart by three blocks 15 located at equal radial angles round the plates 13, 14. The ends of the blocks 15 are optically worked. Alternatively, a plate with turret portions or a ring of material may be used in place of the blocks 15. Each construction may be ' housed in a gas-tight chamber 7 provided with an optically worked window 8, and means for adjusting the gas pressure and of indicating the sameby electrical discharge.