Interpretation of the Faust equation for a conventional refracting prism

Abstract

The Faust formula for a conventional refracting prism is interpreted in terms of the angle of incidence ( i 1) and the angle of deviation (δ). Three new possibilities emerge, namely: 1. (a) keeping the angle of incidence ( i 1) constant and varying the angle of deviation (δ); 2. (b) keeping the angle of deviation constant and varying the angle of incidence ( i 1); 3. (c) modification of the closed forms of Murty's expression and its equivalence to (b). Using paraxial approximation and keeping the angle of incidence ( i 1) and angle of deviation (δ) constant we obtain a relation between the refractive index and the base length ( b) of a prism and, in principle, this is equivalent to the Marcuse variation for optical fibres. The condition for a Littrow prism, as well as for polarized radiation is derived. An expression to estimate the spectral bandwidth (SBW) of the instrument is also derived. Experimental values of refractive index at different wavelengths are within confidence limits.