Caractères communs aux nouvelles méthodes de spectroscopie interférentielle ; Facteur de mérite

A " factor of merit " W = MR/TB03B1 is defined for any spectroscopic device, where R is the resolving power, M the number of spectral elements analysed during the total time T,B the lownt utilizable spectral brilliance and 03B1 is an exponent having the value 1 if photon noise limits sensitivity, ana the value 2 if receiver noise is preponderant. This figure of merit is, amongst other factors, proportional to : 2014 The solid angle 03A9 subtended by the isolating diaphragm which must be of such diameter to yield an effective resolving power R. 2014 The transparency 03C4 (or 03C42 in the case where receiver noise limits sensitivity). 2014 The number m of spectral elements analysed simultaneously Most of the developmental work in spectroscopic technique has as its aim the improvement of one, or several, of these factors. The Fabry-Perot interferometer and devices using a Michelson interferometer, or more generally, systems having a rotational optical symmetry, give a value of 03A9 much greater than a system not having this symmetry. It is explained at the end of the article that such systems require for their operation semi-transparent layers (or equivalent devices) which give a division of luminance of the incidents r s. This gain in solid angle is obtained with all the Fabry-Perot systems using the central zone of the interference system or complete rings, in the devices of P. Fellgett, L. Mertz, J. Connes, and also in the new method of P. Connes which employs the selection by the amplitude of interference modulation. Still further improvement in the allowed solid angle is obtained if the interfering rays are superimposed by the means of an afocal system : this is achieved, for example, in the spherical FabryPerot of P. Connes, which can be used in the domain of very high resolution. The photographie methods allows all the specral elements to be registéred simultaneously ; LE JOURNAL DE PHYSIQUE ET LE RADIUM TOME 19, MARS 1958, Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphysrad:01958001903022300