Answer Happy

a) A particular optical diffraction grating has slits of width a and opaque sections of width b. When illuminated by light of wavelength = a, the grating produces 3rd order principal maxima but not 4th order. (i) Calculate the maximum possible value of a/b. [4] (ii) Sketch the variation of transmitted intensity with sin 0, where is the trans- mission angle. [2] Your sketch should indicate the envelope function derived from diffraction from a single slit and the principal maxima within its central peak. b) The emission spectrum for a particular light source is shown on the left below. (i) For this source state the central wavelength, A, and the line-width, AX. (ii) Derive an expression for the frequency bandwidth, Af in terms of X and AX. (iii) Hence calculate Af and the coherence time of the source. 4cm Tissue paper 545 546 547 10cm Wavelength (nm) 3 Intensity N - [1] [3] [3]