A Digital Recording Double Fabry-perot Spectrometer

A simple and reliable recording double Fabry-Perot spectrometer is described. The linear increase in the first etalon was achieved as usual by means of a pressure reservoir of 200 atm. and a small glass capillary tube. With a second pressure reservoir and a needle valve, the flow rate of which could be changed by a servomotor, the pressure in the second Fabry-Perot was increased. The difference in pressure between the two systems was measured by a mercury manometer, into the limbs of which two 15 y platinum wires are immersed. The deviation of the pressure difference changes the lengths of the wires not submerged in the mercury, which means a change of resistance. This variation was detected in a bridge and the amplified signal was used to drive the servomotor of the needle valve thereby increasing or lowering its flow rate. In this way the pressure difference could be kept constant to less than f0.03 mm Hg. RBsumB. On dkcrit un spectrometre enregistreur double Ctalon Fabry-Perot d'un fonctionnement simple et sBr. Dans le premier Ctalon on fait croitre la pression lineairement a l'aide d'une bouteille a 200 atrn. et d'un petit capillaire en verre suivant le procCdk habituel. On augmente la pression dans le second Ctalon a l'aide d'une seconde bouteille et d'un robinet A pointeau asservi. La diffkrence de pression entre Ies deux syst5mes est mesurke par un manombtre a mercure dans les branches duquel sont immergCs deux fils de platine de 15 p. Un changement de la diffkrence de pression modifie les longueurs de fil Cmergeant du mercure et par suite la rksistance. Cette variation de resistance est mesuree avec un pont et le signal amplifie est utilise pour commander le servomoteur du robinet a pointeau, ce qui modifie son debit. De cette faqon la difference de pression peut Etre maintenue constante a moins de 0,03 mm Hg prks.