A simple question on Wave Optics?

The angle of incidence in air is α_a = 45 degrees so the angle in the glass is α_g = asin(sin(45)/1.5) = 28 degrees. If the width of the beam in air is w_a, than the width of the spot on the glass is w_s = w_a/cos(α_a) = w_a/sqrt(0.5) and the beam width in the glass is w_g = w_s cos(α_g) = w_a/cos(α_a) cos(asin(sin(45)/1.5)) = 1.25 w_a.