You would like to create a reflection grating like the one shown at the right with an incident angle (?) of 41°. Compute the number of lines per centimeter that must be etched in the grating for each of the following conditions:

(a) Explain a first order diffraction angle (?) of -35° for visible light of 400 nm wavelength.

(b) Explain a first order diffraction angle (?) of -35° for infrared light of 1.50 × 10-3 cm wavelength.