(a) An interference filter is to be constructed for isolation of an absorbance band at 1600 cm-1. If it is based on first order interference what should the thickness of the dielectric layer be? Note the refractive index = 1.25. Also what other wavelengths would be transmitted? (b) (c) (6 marks) Compare and contrast an echelle monochromator from an echelette monochromator. Illustrate your answer. (14 marks) Why are photomultiplier tubes not suitable for the IR region? List some of the ideal characteristics of transducers for the IR region. (5 marks)