From the figure, n = (CB + BD); and n = d(sin i + sin r) where i is the angle of incidence and r is the reflection angle; n is the diffraction order.If an echellete grating that contains 1450 blazes/mm was irradiated with a polychromatic beam at an incident angle of 48 degrees to the grating normal, calculate the wavelengths of radiation that would appear at an angle of reflection of +20, +20 at n= 1, and n=2.

W Diffracted beam at reflected angler 2 Grating Monochromatic normal beams at 3 incident angle i D A B